Psych Notes: Brain Cells, Neuron Anatomy, Synaptic Transmission (PDF)

Brain Cells: ​ Types of Brain Cells: ○​ Neurons: These are the "messengers" of the brain (86 billion neurons!). Signal changes in the environment, internal states, action plans, etc. ○​ Glia: Support Neurons. Think of them as the "helpers" or "maintenance crew"....

Brain Cells: ​ Types of Brain Cells: ○​ Neurons: These are the "messengers" of the brain (86 billion neurons!). Signal changes in the environment, internal states, action plans, etc. ○​ Glia: Support Neurons. Think of them as the "helpers" or "maintenance crew". ​ Regulate chemical content of extracellular space (astrocytes) and insulate axons of neurons (oligodendrocytes, Schwann cells). More glia than neurons—just like helpers in a team. ○​ Memory Trick: "Neurons are the messengers, Glia are the helpers." Imagine a huge team with billions of messengers sending notes and helpers making sure everything runs smoothly. ○​ Other cells: Ependymal cells (line fluid filled ventricles and guide cell migration), Microglia (remove debris), Vasculature (blood vessels). Neuron Anatomy: ​ Parts of a Neuron: ○​ Cell Membrane: Lipid bilayer (2 fat layers), contains proteins, e.g. receptors, channels ​ Think of this as the “gatekeeper,” controlling what comes in and out. ○​ Dendrites: receive input from other neurons at synapses (connections between neurons) ​ Imagine these as “antennae” receiving signals from other neurons. ○​ Axon: Provides input to other neurons ​ This is the “highway” where signals travel, leading to other neurons. ○​ Axon Hillock: site of action potential (electrical pulse) generation- action potential generated ○​ Axon Terminal: Part of synapses; The “mailbox” that sends the message to the next neuron. ○​ Cell body (Soma) functions: ​ Gene expression and transcription (nucleus) ​ Protein synthesis (Rough ER, ribosomes) ​ Protein sorting (Smooth ER, Golgi apparatus) ​ Generating Cellular respiration/ energy (mitochondria) ​ Fluid inside cell called cytosol ​ Remember ○​ "Dendrites catch signals, Axon sends them."  ○​ "Hillock launches the signal, Terminal sends it out." Electrical Theory Basics: ​ Electric Charge: ○​ Protons= Positive, Electrons= Negative ○​ Atom has a Positive charge when there are LESS electrons ○​ Negative charge means MORE electrons ​ Important Ions: Na+ (Sodium), K+ (Potassium), Ca2+ (Calcium), Cl– (Chloride). ​ Remember NaK (NaK, sounds like "knock")—“Knock! Na+ is outside, K+ is inside!” Electric Field: ​ An electric field is created by positive and negative charges. ​ Positive ions move towards negative charges, and negative ions move towards positive charges- like a magnet Electric Potential: ​ Electric potential is the energy needed to move a positive ion. ​ Positive ions have more energy when close to a positive charge and lose energy as they move towards negative charges. Potential Difference: ​ Potential difference is the difference in electric potential (energy) between two points. ​ Measured in volts (V)—in neurons, it’s usually in millivolts (mV). Current: ​ Current is the movement of charged particles (like Na+ and K+) from one point to another Ion Concentration Gradient: ​ The cell membrane separates ions and is not permeable to them. ​ There’s a concentration gradient: different ion levels inside vs outside the neuron. ​ Ions flow from high to low concentration. ​ HIGH potassium (K+) inside the cell and High sodium (Na+) outside the cell Ion Channels: ​ Ion channels are selectively permeable to specific ions. ​ They span the membrane and allow ions to pass between the inside and outside of the cell. Membrane Potential: important because changes in membrane potential code information Key facts: ​ At the resting membrane potential, there is a higher concentration of potassium ions inside the cell and a higher concentration of sodium ions outside the cell. ​ The membrane potential refers to the electrical potential difference between inside and outside of the cell ​ When ion channels open, positive ions will move toward more negative compartment. ​ Resting Membrane Potential: Inside the cell is more negative compared to the outside due to proteins having a negative charge. Remember the phrase "At rest, it's a 'negative' vibe." ​ Depolarization: Cell gets excited and membrane potential becomes less negative (or more positive). ​ Hyperpolarization: The opposite; it gets even more negative like overdoing the chill vibes. ○​ "Depolarize: Get excited (less negative)." ○​ "Hyperpolarize: Get super chill (more negative)." Ion Movement & Equilibrium Potential: ​ Ions will diffuse evenly across membrane if there are no other driving forces (diffusion direction down conentration gradient ​ Movement of uons is determined by concentration gradient AND electric potential difference (membrane potential) ​ Equilibrium Potential (E ion): The electrical potential that EXACTLY balances ionic concentration gradients. ​ Key Ion for Resting Potential: Potassium (K+), as neurons are most permeable to it at rest. Leak currents through potassium channels at rest- They leak through channels creating a negative charge inside the cell. Voltage Gated Ion Channgels ​ Imagine these channels as “doors” that open based on the membrane’s electrical charge. Na+ and K+ are like VIP guests at a party—only allowed in when the conditions are just right. ​ Charged protein subunits of channel change conformation based on membrane potential ​ Ligand gated Ion channels: transmitter/messenger (ligand) opens channel, binding of ligand changes channel conformation (AMPA positive ion channel and GABA receptor is the chloride channel) ​ Membrane potential threshold ○​ Depolarization: Na+ channels open when membrane depolarizes (becomes more positive), causing Na+ influx.  ○​ Channels stays open for a brief period and cannot be immediately reopened again because the channel is inactivated (Absolute Refractory Period) ○​ Threshold: critical value of membrane potential at which the Na+ channels open, generating an action potential. (membrane potential around -45mV generates action potential). ​ Memory Trick: "Depolarize = Na+ rush in (party time), Repolarize = K+ leaves (calm down)." Action Potential Propagation: Which of the following is the major driving force for the rising phase of action potentials? ​ Answer: The influx of sodium ions through sodium channels. Not the efflux of potassium ions through potassium channels because The efflux of positively charged potassium ions makes the outside of the cell more positive. It contributes to the falling phase of action potentials, getting the membrane potential back to the resting potential. ​ How Action Potential Travels: ​ Rapid change in membrane potential, ie a brief pulse ​ “All or nothing” event (-70 mV to +30mv and back to -70mV) ​ Carries information long distances along axon to connected cells ​ After absolute refractory period, can generate more spikes if cell depolarized to threshold ○​ Think of it like a wave traveling down a row of dominos. When one ion enters, it sets off the next "domino," propagating the signal down the axon. Depolatizing phase: sodium moves in sodium channels open, inward sodium current (panel b above) Hyperpolarizing Phase: potassium moves out sodium channels close, more potassium channels open, outward potassium current (resets potential) (panel c above) -​ To continue generating action potentials, we need to re-establish concentration gradients by moving sodium back out of the cell and more potassium back in Sodium potassium pump: It maintains the concentration gradients by moving sodium out and potassium into the cell against their gradientsprotein that transports Na+ and K+ back across the membrane against their concentration gradient ; consumes more ATP energy Action potential path: It begins at the axon hillock, generates along the axon with a chain reaction mechanism, and reaches the axon terminal. -​ Action potential travels from the axon hillock to axon terminal -​ Sodium influx at start of action potential depolarizes membrane just ahead to threshold -​ Chain reaction (ie action potential generates and regenerates along axon) -​ Action potential spreads along membrane with conduction velocity -​ Action potential can also travels towards cell body, back propagation Summary: ​ Cell membrane separates ions: More sodium outside cell, More potassium inside cell ​ Electric potential difference across cell membrane: Resting membrane potential: inside of cell more negative than outside ​ Action potential generated when cell depolarized to threshold: Sodium channels briefly open causing Na+ influx, Membrane potential repolarizes when potassium channels open causing K+ efflux ​ Action potential transmitted along axon to next cell across synapse: Lecture 2: Single-Neuron Recordings: ​ Intracellular recordings: Measure action potentials and subthreshold membrane potential fluctuations of targeted cell. ​ Extracellular recordings: Record action potentials (spikes) from nearby cells, sort spikes based on shape, and sum subthreshold fluctuations into local field potentials (LFP). ​ Intracellular recordings reveal both subthreshold dynamics and action potentials, whereas extracellular recordings mainly record spikes and summed fluctuations as local field potentials Electrode Types Used in extracellular recordings ​ Classical few microns of metal exposed at tip), Matrix (record from multiple populations), Laminar probes (multiple electrode contacts), Utah array (only records cerebral cortex because it can not go deep but it is wide (100 cells)). ​ Neuropixels probe offers high-density, high-precision measurements Electrode Characteristics: ​ Small exposed tips have high resistance (harder for currents to flow through), sample smaller areas, and are better for isolating individual neurons  ​ Impedance: a measure of resistance plus electrode capacitance (ability to store charge) ○​ Higher impedance allows smaller, fine-tipped electrodes to isolate spikes from individual neurons, while larger tips (e.g., ECoG) can't isolate single cells. ○​ Further away = smaller amplitude of the spike and vice versa Local Field Potentials (LFP): small fluctuations summed up by nearby neurons ​ a measurement of the combined electrical activity generated by a large group of neurons within a small area of the brain, essentially reflecting the "collective" electrical signal produced by nearby neurons rather than individual spikes ​ LFP from depth electrodes reflects up to 1,000 cells, mainly within 250 microns. ​ ECoG: Electrodes on exposed brain surface (subdural), mainly capturing superficial cortical layers, often used in epilepsy research. Electroencephalography (EEG): the head cap (crazy woman who played all those levels of video game in greys) ​ EEG records synchronized neuron activity (e.g., pyramidal cells), typically from the scalp. Non-invasive but low spatial resolution and poor access to deep brain structures. ​ Reflects 100s of thousands to millions of cells ​ Summation of synchronized activity of neurons with similar spatial orientation (synched) ​ It is hard to localize the activity directly because the skull smears the activity making it hard to identify the specific location of activity Functional Magnetic Resonance Imaging (fMRI): ​ fMRI measures BOLD (blood oxygen level dependent) signals, reflecting subthreshold neural activity, with better spatial than EEG (2x2x2mm³) but worse temporal resolution (every 2s and alot can happen between 2 seconds). ​ It works by exciting hydrogen atoms with magnetic fields as hydrogen atoms have magnetic dipoles and we have lots of water with hydrogen in us ​ Blood oxygenation changes reflect neural activity changes Which of the following neural signals does the fMRI recording most closely reflect? Answer: LFP Spatial resolution and size of signal changes ​ Voxels: Brain divided into small cubes (e.g., 2x2x2mm³), used in fMRI studies with changes in signal size around 2%. 100,000 voxels is common for FMRI Spike Rate Code (gold standard)- number of spikes in a given interval ​ What is it?: The brain often encodes information based on the number of spikes a neuron fires within a given period of time. This is called spike rate. ​ How it works: When a stimulus (like a sound or light) becomes stronger or more intense, neurons typically fire more spikes in response. This increase in the number of spikes helps to communicate the intensity of the stimulus.​ Example: ○​ If you're seeing a dim light, the neurons responsible for processing that visual stimulus might fire only a few times. ○​ But if the light becomes brighter, those neurons will fire more frequently to signal the increase in intensity. Pooled Response Code ​ What is it?: In this coding method, the brain looks at the total number of spikes coming from multiple neurons during a specific time period. Instead of just focusing on one neuron, the brain integrates activity from many neurons at once. ​ How it works: By pooling responses from several neurons, the brain can get a clearer and more reliable signal because it reduces "noise" (random variations) from individual neurons that might fire in unpredictable ways.​ Example: If you have a group of neurons firing in response to an object you're looking at, pooling their responses can help create a stronger, more accurate representation of that object. Spike Timing Codes (Temporal Codes)  ​ What is it?: Spike timing codes focus on when neurons fire. Rather than just looking at how many spikes there are, the brain may also pay attention to the timing of those spikes relative to each other. ​ Two types of spike timing codes: ○​ Spike Pattern Code: This involves the exact pattern or sequence in which neurons fire their spikes over time. For example, some neurons might fire in quick succession, while others might have a pause between spikes. This pattern could represent different types of information. ○​ Spike-Phase Code: This refers to the timing of neuron spikes in relation to the phase of brain oscillations (brain waves). Essentially, neurons might fire at specific points in the rhythm of brain activity, and that timing can encode extra layers of information. Labeled-Line Code ​ What is it?: The labeled-line code is a way the brain might encode information based on which specific neurons are firing AND how many spikes they produce. BOTH ARE IMPORTANT. It's like each neuron has its own "label" or role in a system, and the brain can use which neurons are active to determine the kind of information being processed. ​ How it works: Some neurons may be specialized for processing certain types of information. For example, certain neurons might be dedicated to detecting light, while others might be sensitive to sound. When these specialized neurons fire, the brain can decode the type of information based on which neurons are firing and the number of spikes they send. Decoding neural activity: Pattern Classifier ​ What is it?: A pattern classifier is an algorithm that takes data from multiple neurons (multivariate neural activity) to predict what category or class an image or stimulus falls into. ​ Encode: map stimulus to response, Decode: map response to stimulus ​ How it works: The classifier looks at the patterns of neural firing (like which neurons are firing and at what rates) and learns how these patterns correlate with specific stimuli. ​ 2 step process for decoding: Training step then test step Training Step ​ Goal: To train the classifier so it can recognize patterns in neural activity and link them to specific conditions or categories (like images, actions, or sounds). ​ How it works: ○​ The system is provided with a subset of data (neural activity from different neurons). ○​ The classifier learns how neural patterns correlate with the categories (e.g., an image of a spider or the Tower of Pisa). ○​ There are two types of classifiers: linear (simple relationships) and non-linear (more complex relationships). b) Test Step  ​ Goal: To test the classifier’s ability to predict new data. ​ How it works: ○​ The classifier receives new data (neural activity from the brain). ○​ It predicts the category the data belongs to based on the patterns it learned during training. ○​ Example: If new data corresponds to a “gray dot” in the visual example, the classifier might predict it belongs to the "Tower of Pisa" category. Decoding spike rates: How it works: Imagine you have several neurons (N neurons) and several images (K images). Each neuron fires a certain number of spikes when it is shown an image. ​ In the training step, different images (like a spider or the Tower of Pisa) correspond to different spike rates (represented by red or blue dots). ​ In the test step, the classifier will assign new spike data (represented by a gray dot) to the closest category based on the training data. More sites = more accurate classification performance Challenges with FMRI Data ​ FMRI and Noise: While FMRI (Functional Magnetic Resonance Imaging) is non-invasive and allows researchers to measure brain activity in real time, it tends to have more noise than other methods. ○​ How it works: FMRI measures blood flow changes related to neural activity, but these signals can be noisy and require averaging across multiple trials for accuracy. ○​ Issue: Decoding FMRI data from a single brain scan or image presentation can lead to inaccurate results due to this noise. Neural Prostheses: Connecting Brain Activity to Action -​ What do they measure: -​ Spikes, but requires invasive technique (Ideally record spikes and LFP) -​ LFP, but requires invasive technique -​ FMRI is non-invasive, but not portable -​ EEG is non-invasive and portable (reducing decoding accuracting with EEG (and FMRI) Key requirements: ​ Stable, long-term recordings from a large number of neurons. ​ Efficient real-time analysis of neural activity to produce immediate feedback or control actions. ​ Brain plasticity, which means the brain needs to adjust and adapt to the feedback from the prosthetic device over time. Types of Neural Prostheses: ​ Intracranial implants: These are invasive devices that record spikes and/or local field potentials (LFPs) from within the brain. ​ EEG-based devices: These are non-invasive and portable, making them easier to use outside of a clinical setting. SUMMARY: ​ Neural codes fall into two main categories: -​ Spike rate code -​ Spike timing code ​ Much evidence to support spike rate coding in the brain: ○​ Decoding on the basis of spike rate can predict stimuli well ○​ General agreement among neuroscientists that spike rate is important neural code ​ However, there is evidence that spike timing codes may also be used in the brain:  ○​ There have been reports that spike timing information can improve decoding ○​ But how do we know if the brain uses the information available in spike timing? ○​ Need causal data! Need to directly manipulate spike timing and change behavior accordingly ​ Neural decoding and prostheses show how informative different neural codes are: – Ideally, to understand the brain, need to make accurate predictions about its behavior, fix it when it is damaged, and build working models Quiz: Which of the following statements is False regarding the membrane potential? Answer: The membrane potential always ranges between -65 mV and -70 mV FALSE -​ The membrane potential can vary across a much wider range; the “resting membrane potential” commonly ranges between -65 mV and -70 mV. True Statements: -​ At the resting membrane potential, there is a higher concentration of potassium ions inside the cell and a higher concentration of sodium ions outside the cell. -​ The membrane potential refers to the electrical potential difference between inside and outside of the cell -​ When ion channels open, positive ions will move toward more negative compartment. 01/28/2025 1. Brain Anatomy Overview ​ Cerebral Lobes: The brain is divided into different lobes (frontal, temporal, parietal, occipital), each responsible for specific functions like motor control, sensory perception, and vision. ​ Frontal= motor control, decision making and planning ​ Occipital = vision ​ Temporal : hearing/ higher level vision ​ Parietal = touch, spatial transformations  ​ Cortical Areas: These are regions of the cerebral cortex that process sensory inputs and control motor functions. ​ Subcortical (below the cortex) Regions: These are deeper brain structures (like the thalamus and basal ganglia) involved in functions such as sensory processing, movement, and emotions. 2. Navigating the Brain (Anatomical Terms): ​ Scientific terms: ○​ Anterior/Rostral (front) ○​ Posterior/Caudal (back) ○​ Dorsal (top) ○​ Ventral (bottom) ○​ Lateral (side) ○​ Medial (middle) 3. Brain Circuits: ​ Sensory Pathways to the Cerebral Cortex: Sensory info travels through the thalamus to the primary sensory areas in the cortex (like vision or touch). ​ Pathways Across the Cortex: After initial processing in primary areas, info moves to secondary and higher-order areas for further processing and interpretation. ​ First Order Thalamic areas: areas that receive major input directly from the sensory periphery (eye, ear, skin) 4. Hierarchical Organization of the Cerebral Cortex: ​ The cerebral cortex is organized in layers and regions that process information in a hierarchical manner. This means the brain processes information in stages, from simple to complex. ○​ Primary Sensory Areas: These are the first areas that receive sensory information (e.g., touch, sight, sound). They process basic details like shapes, colors, or textures. ​ Example: The primary visual cortex processes simple features like line orientation (is a line vertical or horizontal?). ○​ Secondary Sensory Areas: These areas take the basic sensory information and start to make more complex associations or refine the details. ○​ Higher-Order Areas: These areas process more abstract or complex information, like recognizing objects, forming concepts, or thinking about goals and plans. (more anterior) ​ Example: The inferior temporal cortex helps recognize objects, and the prefrontal cortex helps think about goals and decision-making. Feedforward Pathways: ​ Feedforward means information flows from the back (posterior) to the front (anterior) of the brain.  ○​ These pathways carry information from the sensory environment to be processed by the brain. ○​ As the information moves forward through the brain, it becomes more complex and abstract. ​ Example: In vision, sensory information like line orientation (simple) moves from the primary visual cortex to higher-level visual areas where the brain processes more complex details like recognizing faces or scenes. Feedback Pathways: ​ Feedback means information flows from the front (anterior) to the back (posterior) of the brain. ○​ These pathways carry information that influences how sensory information is interpreted or processed. Feedback can adjust processing based on things like goals, attention, or predictions. ○​ Example: If you are looking for a friend in a crowd, your brain’s feedback pathways can help filter out distractions and amplify the focus on faces, guiding attention to match your goal (finding your friend). 5. Pathways from Primary Sensory Cortex to Higher-Order Cortex: 1. Pathway of Sensory Information: Sensory Input: ​ Information starts at sensory organs (like eyes, ears, skin), where external stimuli (e.g., light, sound, touch) are detected. First-Order Thalamus: ​ The first-order thalamus acts as a relay station. It receives sensory input directly from the sensory organs (like the eyes or ears) and sends it to the primary sensory cortex. ​ For example, visual information from the eyes is processed by the lateral geniculate nucleus of the thalamus before being sent to the primary visual cortex. Primary Sensory Cortex: ​ The primary sensory cortex (like the primary visual cortex, primary auditory cortex, etc.) processes simple and basic features of the sensory information (e.g., shapes, sounds, or textures). Secondary Sensory Cortex: ​ After processing in the primary sensory areas, the information moves to the secondary sensory cortex. Here, the brain starts refining or integrating more complex details about the sensory input (e.g., color, depth, or patterns). ​ Example: In vision, the secondary visual cortex helps combine simple features to recognize more complex objects, like a face or a tree. Higher-Order Thalamus: ​ Before reaching the higher-order sensory cortex, the information passes through the higher-order thalamus. This thalamic region helps integrate and relay processed sensory information from secondary cortical areas to more advanced areas in the brain. ​ Hypothesis: indirect pathways facilitate processing of only the behaviorally relevant information in the cortex ​ The higher-order thalamus helps further refine and direct the information to the right cortical areas for higher-level processing. Higher-Order Sensory Cortex: ​ The higher-order sensory cortex (such as the inferior temporal cortex for object recognition or prefrontal cortex for planning) processes the most complex and abstract aspects of the sensory information. ​ Example: In the inferior temporal cortex, sensory information from the primary visual areas is integrated to recognize full objects, faces, or scenes. 2. Indirect Pathways Between Cortical Areas via Higher-Order Thalamus: ​ In addition to the direct sensory pathways, there are indirect pathways where information is sent from one cortical area to another via the higher-order thalamus. ​ These pathways allow the brain to send processed sensory information between secondary cortical areas and higher-order cortical areas for more advanced processing and decision-making. Potwntiall also facilitates the processing of only the behaviorally relevant information in the cortex Summary: 1.​ Sensory input (from external stimuli) → First-order thalamus (relay station) → Primary sensory cortex (basic feature processing) → Secondary sensory cortex (refining details) → Higher-order thalamus (integrates and directs to higher cortical areas) → Higher-order sensory cortex (complex processing and interpretation, e.g., object recognition, planning).​ 2.​ Indirect Pathways: Sensory information can travel between cortical areas through the higher-order thalamus, allowing for more complex processing and integration across different regions of the brain. 6. Parallel Pathways Across the Cerebral Cortex: ​ Dorsal Pathway ("How"/"Where"): Involved in guiding sensory-motor actions. Helps you determine "where" something is or "how" to interact with it. ​ Ventral Pathway ("What"): Involved in identifying objects. Helps you recognize "what" an object is. 7. Cerebral Cortex Organization: ​ 6 Layers in the Neocortex: The neocortex is organized into six horizontal layers, with each layer having a specific function. Layers 4, 2/3, 5, and 6 are key in receiving and sending information to/from other brain areas. -​ Motor Cortex: Layer 5 (large pyramidal cells) is prominent, sending motor commands to muscles -​ Sensory Cortex (e.g., Visual Cortex): Layer 4 is thicker, receiving sensory information from the thalamus. -​ Prefrontal Association Cortex:: Has a complex structure with more layers (especially layer 4, which is involved in integrating information from different brain regions). ​ Cytoarchitectonics: The arrangement of neurons in the brain. This arrangement can vary by brain region. 8. Cortical Columns and Minicolumns: Vertical (radial) organization of neurons means that if you go down through the layers of the brain, you'll find groups of neurons that tend to work together and respond in similar ways. ​ When you move an electrode up and down (perpendicular to the surface) in the brain, neurons in the same column tend to respond to the same kind of information, like a specific location or feature of a stimulus (e.g., the color of an object, or where it’s located in space). ​ These neurons are organized into columns (called macrocolumns), which are about 0.4-0.5 mm wide, and smaller minicolumns inside them (around 30-50 microns wide).  ​ Both columns and minicolumns repeat across the cortex, helping to organize the brain's processing of information. 9. Different Types of Cells in the Brain: ​ Excitatory Cells: These cells promote action potentials, making neurons more likely to fire. Ex: pyramidal, stellate (sometimes) ​ Inhibitory Cells: These cells prevent action potentials, reducing neuron activity- hyprpolarize/ inhibit cells (more localized) Ex: double bouquet, small and large basket ​ Types of Cells: Some of the common ones include pyramidal cells (often excitatory), basket cells (inhibitory), and stellate cells (usually excitatory). 10. Canonical Microcircuit of the Cerebral Cortex: -​ The canonical microcircuit organizes the brain to efficiently process sensory information while allowing for feedback adjustments. This makes the brain flexible, helping us focus attention, filter distractions, and adapt processing to the context. ○​ Layer 4: Receives sensory input (feedforward from thalamus or other areas). ○​ Layer 2/3: Sends information to other cortical areas (feedforward). ○​ Layer 5: Sends information to subcortical areas (e.g., motor control). ○​ Layer 6: Sends feedback to thalamus or other cortical areas. ○​ Layer 1: Receives feedback from other areas (important for modulation of sensory input). 11. Differences in Brains Across Species: ​ There are structural differences in the brains of different species, especially in higher-order areas like the prefrontal cortex, which is more developed in humans than in other animals. Brain Size and Complexity: ​ Mouse: Small brain, mostly instinct-driven, limited cognitive flexibility. ​ Macaque: Larger brain with more complex processing and social behaviors. ​ Human: Much larger, highly complex brain with advanced cognitive abilities (e.g., abstract thinking, problem-solving). Prefrontal Cortex: ​ Mouse: Small prefrontal cortex, limited executive functions (e.g., planning, decision-making). ​ Macaque: Larger prefrontal cortex, capable of more complex planning and problem-solving. ​ Human: Very large prefrontal cortex, crucial for abstract thinking, decision-making, and language. Language: ​ Mouse: No ability to understand or produce language.  ​ Macaque: Some vocal communication but no language. ​ Human: Complex ability to understand and produce spoken and written language. Cortex Structure: ​ Mouse: Simplified cortex, fewer layers (less complex processing). ​ Macaque: More layers and complex areas for higher cognitive tasks. ​ Human: Highly complex, layered cortex with specialized regions for advanced reasoning, language, and social behavior. Brain Networking 1. Brain Circuits: ​ Cortico-striatal-thalamic pathways: ○​ Involve the basal ganglia (striatum) and the thalamus, playing a key role in action selection and reinforcement learning. ○​ Basal ganglia helps decide which action to take based on past experiences (reinforcement learning). ○​ Regulares information processing in the cortex ​ Increased striatal activity can disinhibit thalamus (via direct pathway) ​ Nearly all of the cerebral cortex projects to the striatum EXCEPT for the primary visual cortex and primary auditory cortex. ○​ Example: Involved in motor control (e.g., starting or stopping movements). ​ Hyperdirect pathway: cortex to subthalamic nucleus ​ Direct Pathway: striatum to GP (globus pallidus) internal segment ​ Indirect Pathway: striatum to globus pallidus external segment to subthalamic nucleus to globus pallidus internal segment ○​ The net effect of cortex on subthalamic nucleus is excitatory in both indirect and hyperdirect pathways ​ Cortico-cerebellar pathways:​ ○​ Involve the cerebellum (motor and cognitive functions), which aids in motor learning and automatic movement control (once skills are learned). ○​ The cerebellum receives efference copies (predicted motor commands) from the motor cortex to anticipate the sensory outcome of movements. ○​ Important for both motor and cognitive functions. ​ Cortico-hippocampal pathways: ○​ Connect the cortex and hippocampus, supporting episodic memory and spatial navigation. ○​ The hippocampus helps remember past experiences (episodic memory) and navigate physical spaces. ○​ Parahippocampal (surrounding) areas = parahippocampal cortex, perirhinal cortex, entorhinal cortex 2. Types of Brain Networks: Bigger networks = longer time to transfer information ​ Regular Network: ○​ Every node (or brain area) is connected to its closest neighbors. ​ Random Network: ○​ Connections between nodes are randomly assigned, increasing disorder. ​ Small-world Network: High clustering and small characteristic path length- CEREBRAL CORTEX ○​ Combines features of both regular and random networks. - high clustering ○​ High clustering like regular networks (nodes connected to their neighbors) and small characteristic path lengths (average number of steps from one node to another) like random networks (shorter routes between distant nodes). ○​ Real-world example: “Six degrees of separation” concept — most people can be connected through just six steps. ○​ Example : rich club architecture 3. Network Features and Measures: Brain networks are made up of nodes (brain areas) connected by edges (connections). These can be measured using various features: ​ Node Degree: Number of connections a node has with others. Higher degree = more connections (like a "hub"). ​ Clustering Coefficient: Measures how connected a node’s neighbors are to each other (e.g., how well a group of brain regions work together). As a proportion of the maximum number of possible connections. ​ Path Length: Minimum number of edges to go from one node to another ​ Module: a subset of nodes with high winith-module connectivity and low inter-molecule connectivity ​ Functional connections in the brain are measured by taking the correlations in activity between regions of interest. Brain areas that activate and deactivate together have a stronger functional connection. 4. Brain Network Topology: ​ Hubs: Brain regions with a high number of connections, helping integrate information across areas. → Rich node: node with a large number of connections i.e. high degree node (hub) ​ Rich-club: A group of high-degree hubs that are well-connected to each other, forming a tight subgraph (important for coordinating complex functions). ​ Rich club organization: greater likelihood of high degree nodes forming clubs than low-degree nodes Key Brain Hubs  ​ Precuneus: Important for self-reflection and memory retrieval. ​ Cingulate Cortex: Involved in emotion, cognition, and behavior regulation. ​ Superior Frontal Cortex: Important for higher cognitive functions (e.g., attention). ​ Insular Cortex: Plays a role in awareness, emotional processing, and interoception (sensing internal body states). ​ Thalamus: Acts as a relay station for sensory information and brain-wide communication. 5. Mapping Brain Connectivity: ​ Anatomical Connections: Physical connections between neurons. We can study them through methods like Diffusion MRI, which tracks water diffusion along white matter paths. ○​ Diffusion MRI (non invasive) Tracks how water molecules move along axons, revealing the brain's white matter tracts (connectivity).  ○​ Tracer studies (invasive); tracer molecule injected into brain and travels along axons ​ Functional Connections: Measure how brain areas work together in terms of activity, using tools like fMRI (which measures blood oxygenation) or EEG (measuring brain wave activity). ○​ Fmri may reflect direct or indirect anatomical path between brain areas 7. Brain Network Changes in Disease: -​ In schizophrenia, brain networks are disrupted. -​ One key issue is that there is increased activity in the temporal lobe, which might contribute to hallucinations, particularly auditory ones (hearing voices). -​ And there are reduced connections in the frontal lobe, which could explain poor speech and impaired cognitive control. The decreased connectivity in the frontal regions makes it harder to regulate thoughts and actions, affecting communication and higher cognitive functions. 2/4/2025 Receptive Fields: 1. Overview of Receptive Fields and Their Role in Sensory Perception: ​ Receptive Field (RF): The region of the sensory world (e.g., visual space, body surface) that a neuron responds to. ○​ Function: Small receptive fields are useful for tasks that require high resolution, like recognizing specific objects or fine textures. Larger receptive fields are helpful for detecting the overall environment or for position invariance—being able to recognize something no matter where it is located. ○​ Having different-sized receptive fields across the brain lets us balance between detail (identifying small features) and context (seeing the big picture), allowing for more efficient processing of the world around us. ​ Importance of RFs: Receptive fields allow neurons to process sensory stimuli, helping us understand where and what objects are. 2. Two Key Questions in Sensory Systems: ​ Where something is: This is determined by spatial resolution, which is influenced by the size of the receptive field. Small RFs offer high spatial resolution (i.e., they can identify specific locations), while large RFs have low spatial resolution but can detect broader areas. ​ What something is: This is influenced by object identification—the size of the receptive field affects the neuron’s ability to identify objects. A smaller RF can identify detailed features (e.g., a specific chair design), while larger RFs allow for identifying large objects or scenes (e.g., a lecture hall). 3. Different Receptive Field Sizes and Their Functions: ​ Small Receptive Field: Offers high spatial resolution, useful for identifying fine details, such as specific objects or features (e.g., a specific seat design).  ​ Large Receptive Field: Offers position invariance, meaning it can detect objects regardless of where they are in the environment, but it cannot identify fine details (e.g., it can tell you it’s a lecture hall but not the specific seat). ​ Intermediate Receptive Field: This field is ideal for detecting objects in a defined space (e.g., identifying who enters or exits a row in a lecture hall). 4. Building Receptive Fields of Different Sizes: ​ Small RFs at Early Stages: Smaller receptive fields are typically found in the initial sensory processing stages, closer to the sensory organs (e.g., the retina, skin). ​ Large RFs through Integration: Larger receptive fields are often created by summing inputs from multiple small RFs. This aggregation creates a broader detection area, useful for object detection at larger scales. USES: ​ To localize and identify small objects, small receptive fields are used for high detail. ​ To identify large objects or scenes, bigger receptive fields provide a broader view. ​ To ensure position invariance, large receptive fields help recognize objects anywhere. Multiple Representations of the Environment: Topographic maps ​ Small receptive fields: Detect fine details. ​ Large receptive fields: Detect larger objects or overall scenes. ​ Different stimulus features (e.g., motion) are also represented. Building Receptive Fields of Different Sizes: ​ Small receptive fields are found early in sensory pathways. ​ Larger receptive fields can be created by combining multiple small ones. ​ Neurons with adjacent small receptive fields can input to one neuron, forming a larger receptive field. Receptive Fields Across Different Dimensions: ​ Visual Receptive Field: Mapped to 2D space, representing areas in your visual environment. ​ Somatosensory Receptive Field: Mapped to the body surface, representing areas of skin or body parts. ​ Olfactory Receptive Field: Mapped to the chemical structure of odors, specifically the carbon chain length of odorants. ​ Numerical Receptive Field: Mapped to the concept of numerosity, or the perception of quantities. Topographic Map: ​ An orderly representation of sensory space, where different neurons have receptive fields for different areas. ​ Nearby neurons represent nearby regions of sensory space, while distant neurons represent distant areas. Disproportionate Representation: ​ Some regions of sensory space (e.g., the fovea in vision) take up more space on the map, allowing for greater sensitivity in those areas. Brain Areas and Sensory Space: ​ Multiple sensory maps exist in the brain (e.g., visual maps). ​ Each visual area (e.g., V1, V2) represents half of the visual field (called a hemifield). ​ The left hemisphere represents the right visual field, and the right hemisphere represents the left visual field. 6. Types of Topographic Maps in the Brain: ​ Retinotopic Map: The visual field is divided into hemifields, with each hemisphere of the brain processing the opposite side of the visual world. A retinotopic map is like a map of the visual world in the brain. It organizes visual space based on how the retina (the light-sensitive part of the eye) is arranged. ​ Visual space is divided into two halves, called hemifields: one for the left side of the world and one for the right side. ​ The brain creates an orderly map of what you see, where nearby neurons in the brain represent nearby parts of the visual world, just like how the retina works. ​ For example, the part of the retina that sees the center of your visual field (like what’s in front of you) has its own specific part in the brain, while the part that sees the edges of your vision has its own spot too. This "map" in the brain helps us make sense of what we see in an organized, spatial way. ​ Tonotopic Map: A tonotopic map is like a map for sound in the brain. It organizes sound based on frequency, or the pitch of the sound (like low or high notes). ​ Different parts of the brain respond to different frequencies of sound, much like how the ear processes different pitches.  ​ Low-pitched sounds are mapped to one area of the brain, and high-pitched sounds are mapped to another area. ​ The brain keeps this map orderly so that nearby neurons respond to sounds that are close in pitch, making it easier for the brain to process complex sounds. This organization helps us distinguish between different tones, like hearing a bass guitar versus a flute. ​ Somatotopic Map: In the somatosensory cortex, there is a somatotopic map of the body surface, with more sensory space devoted to areas with finer motor control or higher sensitivity (e.g., fingertips, lips). →It's like a body-shaped map in the brain that helps us feel and control our movements more precisely. A somatotopic map is how the brain organizes information about the body’s surface, like touch or movement. ​ The brain has an orderly layout where different areas of the brain represent different parts of the body (e.g., hands, arms, legs). ​ Areas with more sensitivity, like the fingers or lips, take up more space in the brain’s map. ​ This map helps the brain process sensory information (like touch) and motor commands (like movement) for each body part in a specific, organized way. 7. Advantages of Multiple Topographic Maps: ​ Efficient Design: Grouping neurons that process nearby sensory space together helps them interact more often, reducing the need for long, complex connections in the brain. This saves energy and improves efficiency. ​ Connection Challenges: Each neuron in a map connects with a limited number of other neurons. If all neurons need the same number of connections, the size of the map affects how much each neuron connects to—larger maps need more complex wiring.  ​ Fine-Grained Maps (Many Neurons): These maps have a large number of neurons, which means each neuron may need longer or more connections to interact with others, making them more complex. ​ Coarse-Grained Maps (Fewer Neurons): These maps use fewer neurons, making it easier to connect distant parts of the map. This helps integrate information from different areas of the sensory world efficiently. 8. Summary of Key Points: ​ Receptive fields are essential for sensory processing, defining the region to which a neuron responds. ​ Topographic maps provide an orderly, efficient way of representing sensory space, with each map devoted to different sensory modalities. ​ The size and integration of receptive fields allow us to balance high-resolution identification of small features and broad detection of large objects or scenes. 2/6/2025 Coordinate Systems Study Notes What is a Reference Frame? ​ A reference frame is also called a coordinate system. ​ It is used to represent the position of objects or events. The origin of the coordinate system is the reference point (e.g., a lectern, your body, the head). ​ Example: To describe your position in a room, you might refer to the lectern as the origin (lectern-centered reference frame), or you might use a mathematical Cartesian coordinate system. Types of Reference Frames 1.​ Egocentric Reference Frames:​ ○​ Position relative to oneself (i.e., your body). ○​ Includes: ​ Eye-centered (retinotopic): The eye as the origin. Position is relative to the eye's gaze (e.g., where an object appears on your retina). 1.​ Imagine you are looking at a tree. When you focus your eyes directly ahead, the tree appears at the center of your retina. If you shift your gaze up or down, the tree will move to a different position on your retina. The position of the tree is therefore described in terms of your eye's gaze direction, or eye-centered coordinates.  ​ Head-centered: The head as the origin. Position is relative to the head's orientation. ​ Body-centered: The body (or body part) as the origin. Position is relative to your body’s position. 1.​ Your body (or a specific part of it, like your hand) serves as the origin of this reference frame. The position of the cup can be described relative to your body. For instance, you might say the cup is 30 cm to your right and 10 cm in front of you. This describes the cup’s position relative to your body. 2.​ Allocentric Reference Frames: ○​ Position relative to something external to you (i.e., not dependent on your body). ○​ Includes: ​ Object-centered: Position is relative to a specific object in the environment. 1.​ You're looking at a chair placed in the middle of a room. The position of the chair can be described in terms of the chair itself—its coordinates don't change based on where you are standing. For example, you might say the chair is 2 meters away from the door, 1 meter to the left of the lectern. The position is described relative to the object (the chair), not you. ​ World-centered: Position is relative to a broader, external environment (like a street map). 1.​ In this system, your position is mapped relative to landmarks or global points of reference (e.g., "the café is 100 meters ahead and to the right of the post office"), independent of your body’s orientation or position. Transformations Between Reference Frames ​ Transformations: The brain can switch between different reference frames, often for spatial navigation or sensorimotor tasks. ​ Example: To reach for an object, the brain must transform visual information (eye-centered) into body-centered coordinates to plan movement. Brain Areas Involved in Reference Frames ​ Parietal Cortex: Primarily uses egocentric reference frames, involved in spatial awareness and body positioning. ​ Hippocampus (Medial Temporal Lobe): Uses allocentric reference frames. This region helps form maps of spatial environments (e.g., a memory of a room layout). ​ Retrosplenial Cortex (RSC) and Posterior cingulate cortex (PCC) : Involved in spatial transformations between allocentric and egocentric reference frames (located between parietal cortex and hippocampus). Role of Head Direction Cells: ○​ These specialized cells are found in several areas of the brain, notably in the anterior thalamus. ○​ Head-direction cells act like a compass: ​ They respond to the direction in which your head is pointing, not your body position. ​ For example, a head-direction cell might fire when your head is pointing north-west, helping your brain know the orientation of your head. ○​ These cells don’t care about the position of your body or how your head is tilted relative to your body—just the direction your head is facing in space. ​ Combining Head-Direction Information with Egocentric Data: ○​ The brain combines head-direction information (from the head-direction cells) with egocentric information (e.g., where objects are in relation to your body). ○​ This helps create a consistent, stable representation of your environment (allocentric map), which doesn't change based on your head's orientation or body movements. ○​ This orientation-invariant representation is critical for navigation and spatial awareness. Interactions Between the Parietal Cortex and Hippocampus ​ Transformation Between Coordinates: The parietal cortex, retrosplenial cortex, and hippocampus work together to convert between egocentric (self-based) and allocentric (external) spatial information during navigation. ​ Egocentric to Allocentric Integration: The parietal cortex provides egocentric information to the hippocampus, helping create a dynamic map of your current location in the environment. ​ Supporting Locomotion: The parietal cortex also uses the hippocampus’ output to guide movement, helping plan the next step in navigation. The Role of Different Reference Frames in Sensory and Motor Processes  1.​ Sensorimotor Transformations (Eye to Hand Coordination):​ ○​ When you see an object and reach for it, the brain must transform the object’s position from eye-centered coordinates to hand-centered coordinates. ○​ Example: You might first know the location of a cup (eye-centered), but to pick it up, the position needs to be transformed into hand-centered coordinates (accounting for your arm’s position). 2.​ Head-direction Cells:​ ○​ These cells exist in the anterior thalamus and respond to the direction of your head (like a compass). ○​ These cells help the brain integrate egocentric information (your position) and allocentric information (external reference), aiding in navigation. 3.​ Pathways Between the Parietal Cortex and Hippocampus:​ ○​ The parietal cortex (egocentric) and hippocampus (allocentric) communicate to help transform spatial information during navigation. ○​ Example: The parietal cortex provides egocentric data (e.g., “I am standing next to the lectern”), while the hippocampus processes allocentric data (e.g., “the lectern is to the left of the door”). Summary: ​ Reference frames are coordinate systems used to describe an object’s position in space. ​ The brain uses two primary types of reference frames: ○​ Egocentric: Relates to your body, such as eye-centered, head-centered, or body-centered. ○​ Allocentric: Relates to external points, such as object-centered or world-centered. ​ Different brain regions specialize in different reference frames: ○​ Visual cortex: Eye-centered ○​ Motor cortex: Body-centered ○​ Hippocampus: Allocentric ​ The parietal cortex and hippocampus collaborate to allow transformations between these reference frames, which are critical for navigation and coordinated actions.  2/11/2025 Synaptic Transmission and Plasticity 1.​ Synapse ○​ Definition: A synapse is the connection between two neurons. Often, the axon of a presynaptic neuron contacts the dendrite of a postsynaptic neuron. 2.​ Neurotransmitter ○​ Definition: A neurotransmitter is a chemical messenger released from the presynaptic neuron to transmit signals across the synapse to the postsynaptic neuron. Gaba is the main inhibitory transmitter in cerebral cortex 3.​ Receptor ○​ Definition: A receptor is a protein in the cell membrane to which neurotransmitters bind. Many receptors are ligand-gated ion channels, meaning they open when a neurotransmitter (ligand) binds. 4.​ Post-Synaptic Potential (PSP) ○​ Definition: A post-synaptic potential is a subthreshold change in the membrane potential of the postsynaptic neuron, caused by the movement of ions through receptor channels. These can be excitatory (EPSP) or inhibitory (IPSP). 5.​ Synaptic Plasticity ○​ Definition: Synaptic plasticity refers to changes in how effectively information is transmitted across a synapse. It involves changes in the magnitude of the PSP elicited by a presynaptic action potential, and it is key for learning and memory. Types of Synapses 1.​ Axo-Somatic Synapse ○​ Impact: Can significantly influence action potential generation in the postsynaptic neuron. 2.​ Axo-Dendritic Synapse  ○​ Common Type: This is the most common type of synapse where the axon of one neuron contacts the dendrite of another neuron. 3.​ Axo-Axonic Synapse ○​ Impact: Can modulate the release of neurotransmitters from the postsynaptic cell. Synaptic Structure ​ Synaptic Cleft: The small space (about 20 nm wide) between the presynaptic and postsynaptic neurons. ​ Synaptic Vesicles: Contain neurotransmitters that are released into the synaptic cleft during transmission. ​ Active Zone ​ Generally each neuron will only contain one type of amino acid or amine neurotransmitter (in addition to neuropeptides) Neurotransmitter Release Mechanism 1.​ Synaptic Vesicle Docking: Vesicles filled with neurotransmitters dock at the presynaptic terminal's "active zone." 2.​ Action Potential Arrival: An action potential triggers an increase in presynaptic calcium (Ca²⁺). 3.​ Calcium Triggers Release: The rise in calcium activates proteins that trigger the fusion of synaptic vesicles with the cell membrane, leading to neurotransmitter release into the synaptic cleft. 4.​ Vesicle Recycling: After neurotransmitter release, the vesicle is recycled for future use. Calcium Triggers Vesicle Fusion ​ SNARE proteins dock vesicle to cell membrane and mediate fusion. ​ Synaptotagmin acts as a calcium sensor and activates fusion. ​ Calcium (Ca²⁺) binds to synaptotagmin, triggering vesicle fusion and neurotransmitter release. Post-Synaptic Receptors 1.​ Ionotropic Receptors (Ligand-Gated Ion Channels)​ ○​ Function: These receptors contain neurotransmitter binding sites on their extracellular domain. When neurotransmitters bind, they open the ion channel. ○​ Effect: The movement of ions through the channel causes a rapid change in membrane potential, either depolarizing (excitatory) or hyperpolarizing (inhibitory) the postsynaptic cell. 2.​ Metabotropic Receptors (G-Protein-Coupled Receptors)​ ○​ Function: These receptors activate G-proteins that influence other cellular processes. They have slower and more prolonged effects compared to ionotropic receptors. 1.​ Transmitter-Gated Ion Channels ○​ Definition: These are specialized proteins (also called receptors) found in the postsynaptic membrane that open when neurotransmitters bind to them. This leads to changes in the membrane potential of the postsynaptic neuron. 2.​ Functional Domains of Transmitter-Gated Ion Channels  ○​ Extracellular Domain: This region contains the neurotransmitter binding sites. When neurotransmitters attach to these sites, they trigger the opening of the channel. ○​ Membrane-Spanning Domain: This part of the receptor forms the ion channel that spans the membrane. When the receptor is activated by neurotransmitter binding, it allows ions to pass through the membrane. How Transmitter-Gated Ion Channels Work 1.​ Ion Movement ○​ When a neurotransmitter binds to the receptor (transmitter-gated ion channel), the channel opens, allowing ions to flow through: ​ Positive Ions (Na⁺, Ca²⁺): When positive ions enter the cell, they cause depolarization, making the membrane potential more positive. ​ Negative Ions (Cl⁻): When negative ions enter the cell, they cause hyperpolarization, making the membrane potential more negative. 2.​ Membrane Potential Change ○​ The opening of the transmitter-gated ion channel leads to a rapid change in membrane potential: ​ Depolarization (more positive): Occurs when positive ions like Na⁺ or Ca²⁺ enter the cell. ​ Hyperpolarization (more negative): Occurs when negative ions like Cl⁻ enter the cell. 3.​ Speed of Effects ○​ Rapid Response: Transmitter-gated ion channels cause a change in membrane potential within 1-2 milliseconds after the action potential reaches the presynaptic terminal. ○​ Duration of Effect: The membrane potential change can last for up to 10 milliseconds, and in some cases, it may last even longer. Different receptor subtypes for transmitter: ​ AMPA: Ionotropic receptor, involved in excitatory synapses. ​ NMDA: Ionotropic receptor, involved in both excitatory synapses and voltage-gated processes. ​ GABA_A: Ionotropic receptor, involved in inhibitory synapses. ​ GABA_B: Metabotropic receptor, involved in inhibitory synapses.  Types of Post-Synaptic Potentials 1.​ Excitatory Post-Synaptic Potential (EPSP) ○​ Example: Glutamate acting on AMPA receptors. ○​ Effect: Depolarizes the postsynaptic membrane, making the neuron more likely to fire an action potential. 2.​ Inhibitory Post-Synaptic Potential (IPSP) ○​ Example: GABA acting on GABA_A receptors; GABA binding to post-synaptic GABA-A receptor will open ion channels and thus leads to an influx of chlorine ions, causing IPSP. ○​ Effect: Hyperpolarizes the postsynaptic membrane, making it less likely to fire an action potential. Synaptic Integration ​ Synaptic Integration: The process by which multiple synaptic inputs (EPSPs and IPSPs) are combined to determine whether a neuron will fire an action potential. ​ Threshold: If the sum of inputs reaches a certain threshold, an action potential will be generated. Synaptic Plasticity 1.​ Short-Term Synaptic Plasticity​ ○​ Definition: Temporary changes in synaptic strength that can last from milliseconds to seconds. ○​ Types: ​ Short-Term Facilitation: Increased synaptic strength after repeated stimulation. ​ Short-Term Depression: Decreased synaptic strength due to prolonged or repeated activity.  2.​ Long-Term Synaptic Plasticity​ ○​ Definition: Lasting changes in synaptic strength, typically occurring over minutes to hours, and crucial for learning and memory. ○​ Types: ​ Long-Term Potentiation (LTP): An increase in the magnitude of EPSP in response to high-frequency stimulation of the presynaptic neuron. 1.​ Big increase in post-synaptic calcium can lead to long-term potentiation (LTP) 2.​ Large increase in calcium ions inside post-synaptic cell induces LTP after high pre-synaptic activity; Long-Term Depression (LTD): A decrease in the magnitude of EPSP in response to low-frequency stimulation of the presynaptic neuron. ​ small increase in calcium ions inside post-synaptic cell induces LTD after low pre-synaptic activity. ​ LTP and LTD are thought to be important mechanisms underlying learning and memory ​ LTP and LTD are input-specific ​ The phosphorylation of AMPA receptor facilitates LTP 3 Mechanisms of Long-Term Potentiation (LTP) 1.​ Increased AMPA Receptor Effectiveness: AMPA receptors become more effective, increasing the postsynaptic response. 2.​ Insertion of More AMPA Receptors: More AMPA receptors are inserted into the postsynaptic membrane, increasing sensitivity to neurotransmitters. 3.​ Increased Neurotransmitter Release: Retrograde messengers (e.g., nitric oxide) increase presynaptic calcium levels, enhancing neurotransmitter release. Mechanisms of Long-Term Depression (LTD) 1.​ Low-Frequency Stimulation: Low-frequency stimulation (e.g., 1 Hz) leads to a small increase in postsynaptic calcium, which reduces synaptic strength and leads to LTD. Role of Calcium in Synaptic Plasticity ​ Large Increase in Post-Synaptic Calcium: Leads to LTP. ​ Small Increase in Post-Synaptic Calcium: Leads to LTD. Summary 1.​ Synaptic Transmission:​  ○​ Action potentials trigger neurotransmitter release from presynaptic neurons. ○​ Neurotransmitters bind to receptors on postsynaptic neurons, leading to changes in membrane potential (PSP). ○​ The type of PSP can be excitatory (EPSP) or inhibitory (IPSP). 2.​ Synaptic Plasticity:​ ○​ Synaptic strength can increase (LTP) or decrease (LTD), affecting the magnitude of the PSP. ○​ Calcium plays a key role in regulating both transmitter release and synaptic plasticity. 3.​ LTP and LTD:​ ○​ LTP: High-frequency stimulation increases EPSP. ○​ LTD: Low-frequency stimulation decreases EPSP. 2/13/2025 Memory Types 1. Declarative Memory vs. Non-declarative Memory: ​ Declarative memory: Conscious recall of facts and events (e.g., facts, personal experiences). ○​ Episodic memory: Personal events and experiences. ○​ Semantic memory: General knowledge about the world (e.g., facts, names). ​ Non-declarative memory: Unconscious learning (e.g., procedural memory like riding a bike, conditioned responses, emotional responses, skills and habitd Amnesia: Retrograde vs. Anterograde Amnesia 1. What is Amnesia? ​ Amnesia refers to a loss or impairment of memory, often due to damage to specific areas of the brain. It can affect different types of memory, including the ability to form new memories or recall past experiences. 2. Types of Amnesia: ​ Retrograde Amnesia: ○​ Refers to the loss of memories that were formed before the onset of amnesia. ○​ The person cannot recall events or information from their past, but they can still form new memories after the injury. ○​ Example: After a brain injury, a person may forget their childhood or recent personal experiences but retain the ability to learn new information. ​ Anterograde Amnesia: ○​ Refers to the inability to form new memories after the onset of amnesia.  ○​ A person may have trouble recalling events that occur after the brain injury or lesion, but memories from the past remain intact. ○​ Example: Patient H.M. (Henry Molaison) suffered from anterograde amnesia after the removal of parts of his hippocampus to treat epilepsy, leaving him unable to form new declarative memories. Studying Brain Lesions to Identify Areas Involved in Memory and Cognitive Function 3. How Brain Lesions Help Identify Memory-related Areas: ​ Studying the effects of brain lesions—either through patients with brain damage or through experimental manipulation in animals—helps identify which areas of the brain are critical for specific cognitive functions, including memory. Insights from Patient H.M. ​ Patient H.M.: ○​ Surgical removal of hippocampus and related areas (perirhinal and entorhinal cortex) to treat epilepsy. ○​ Consequences: ​ Profound anterograde amnesia (inability to form new memories). ​ No impact on procedural memory (e.g., motor skills) or IQ. ○​ Key Insight: The hippocampus is crucial for forming new declarative memories, particularly for episodic memory. ○​ Medial temporal lobe important for declarative memory The Hippocampus Hippocampus functions: – Episodic memory – Spatial navigation ​ Pattern separation: Ability to distinguish similar experiences (e.g., remembering where you sat in class during different lectures). ○​ Pattern separation is the ability to distinguish similar patterns and experiences ○​ Hippocampus contributes to pattern separation ○​ Pattern separation is important to keep memories distinct and avoid confusion  ​ ​ Pattern completion: Ability to recall memories from partial cues (e.g., remembering details from an event when only given some context).​ ​  ​ ​ Hippocampus Role in Memory: ○​ Not a storage site for memories. The hippocampus likely acts as an indexing system to access memories stored elsewhere (e.g., in the neocortex). ○​ Interacts with neocortex for memory consolidation and retrieval, potentially involving the thalamus. Episodic Memory 4. What is Episodic Memory? ​ Refers to remembering personally experienced events. ​ Includes mental time travel (reliving past experiences). ​ Example: Remembering the sights, sounds, people, and events of a specific moment in time. 5. Hippocampus Role in Episodic Memory: ​ Hippocampus binds cortical inputs into integrated memory trace (conjunctive encoding): ​ – Includes pattern separation ​ Hippocampus reinstates previous activity patterns (retrieval): ​ – Includes pattern completion Semantic Memory ​ Refers to general knowledge about the world, not tied to specific personal experiences. ​ Examples: ○​ Names, attributes, and uses of objects. ○​ Historical facts, categories, concepts, and beliefs. ○​ Knowledge of how things work (e.g., "why do people behave this way?"). 7. Brain Regions Involved in Semantic Memory: ​ Lateral and ventral temporal cortex: Involved in processing semantic information. ​ Networks: Includes the angular gyrus, fusiform gyrus, inferior frontal gyrus, and other areas. ​ Semantic memory model: The anterior temporal cortex is believed to be an amodal hub for integrating different sensory modalities. Concept Cells 8. What are Concept Cells? -​ Concept cells usually only respond to consciously recognized stimuli -​ Concept cells respond to stimuli of a certain category, such as various faces, or objects. -​ The concepts that the concept cells respond to are highly specific -​ ​ Found in the temporal lobe (often from patients with epilepsy). ​ Highly specific neurons that respond to specific concepts (e.g., a person’s face, a particular place). ​ Multimodal invariance: These cells can recognize concepts regardless of the modality (e.g., a face is recognized whether seen or described). ​ The temporal lobe contains category-selective cells that respond to specific types of information. ​ Face-selective cells in the inferior temporal cortex respond best to visual images of faces. ​ Category-selective cells in the medial temporal cortex respond to categories like scenes, animals, and food. ​ Concept cells: ○​ Show multimodal invariance (respond to the concept across different sensory modalities). Similar neuronal response to individual or object regardless of whether they were viewed from different angles, identified from text or speech. ○​ Have high specificity for individual concepts. ○​ Are involved in conscious recognition. Cortico-Hippocampal Circuitry 9. Hippocampal Functioning: ​ The hippocampus is involved in episodic memory, spatial navigation, and memory consolidation. ​ It interacts with neocortex and parahippocampal areas (including entorhinal, perirhinal, and parahippocampal cortices). ​ Synaptic plasticity (i.e., the ability of synapses to strengthen or weaken over time) underlies memory formation. function of hippocampus and parahippocampal areas: -​ Pattern separation and pattern completion -​ Spatial navigation -​ Consolidation and retrieval of semantic memory Synaptic Plasticity in Memory 10. Synaptic Plasticity: LTP and LTD can be induced in human temporal cortex, similar to rodent studies: ​ Long-term potentiation (LTP): Strengthening of synapses after high-frequency stimulation (important for memory formation).’ High-frequency (100Hz) stimulation produced LTP ​ Long-term depression (LTD): Weakening of synapses after low-frequency stimulation. Low-frequency (1Hz) stimulation produced LTD ​ These processes are similar in both rodents and humans, particularly in the medial temporal lobe (important for memory). Key Concepts Summary ​ Declarative memory is stored in the neocortex and consolidated in the temporal cortex. ​ Episodic memory and semantic memory are types of declarative memory. ​ Hippocampus plays a central role in episodic memory by aiding in pattern separation and pattern completion, but does not store memories. ​ Concept cells and category-selective cells in the temporal lobe are involved in recognizing specific concepts or categories (e.g., faces, scenes). ​ Synaptic plasticity in the temporal lobe is thought to be the cellular mechanism behind memory formation. FINAL STUDY GUIDE Lecture 1: Introduction to Psych 454  ​ Action Potential Generation: ○​ Resting potential, depolarization, repolarization, hyperpolarization. ○​ Importance of sodium (Na⁺) and potassium (K⁺) ion movement. Lecture 2: Brain Recording Techniques ​ Key Brain Recording Methods: ○​ EEG, fMRI, PET, single-unit recording, and how they differ in terms of resolution and invasiveness. ○​ Lecture 4: Basal Ganglia & Movement ​ Basal Ganglia Pathways: ○​ Direct, indirect, and hyperdirect pathways. ○​ Increased striatal activity disinhibits the thalamus via the direct pathway. ​ Schizophrenia & Brain Networks: ○​ Perturbed brain networks can lead to psychological disorders. Lecture 6: Spatial and Navigational Systems ​ Receptive Fields: ○​ Egocentric vs. allocentric reference frames. ○​ Effect of movement on receptive fields. ○​ Head Direction Cells and how they help with spatial orientation. Lecture 7: Synaptic Mechanisms ​ Neurotransmitter Release: ○​ Mechanism of release of neurotransmitter release  1.​ Synaptic vesicle docked at pre-synaptic “active zone” 2.​ Action potential leads to increased pre-synaptic calcium 3.​ Calcium triggers neurotransmitter release 4.​ Synaptic vesicle recycled ○​ EPSP (Excitatory Post-Synaptic Potential) vs IPSP (Inhibitory Post-Synaptic Potential). ○​ LTP (Long-Term Potentiation) and LTD (Long-Term Depression). Lecture 8: Memory ​ Pattern Separation & Pattern Completion: ○​ Pattern separation: Process of distinguishing similar memories. AB= A + B ○​ Pattern completion: Recalling full memories from partial cues. A +B= AB Which of the following have center-surround receptive fields (choose best answer)? (a) Bipolar cells (b) Ganglion cells (c) Lateral geniculate nucleus (LGN) cells (d) All of the above True statments: (a) Simple cells in primary visual cortex (V1) respond best to oriented lines (b) Complex cells in primary visual cortex respond best to oriented lines (d) Simple cells and complex cells are orientation selective Which of the following is true (choose best answer)? (a) Interaural time difference (ITD) is a location cue for low-frequency sounds (b) Interaural level difference (ILD) is a location cue for high-frequency sounds (c) Head-related transfer function (HRTF) is a vertical (elevation) location cue (d) All of the above