Psych 454 Exam 1

• Neurons signal changes in the environment, internal states, and action plans, with 86 billion in the brain.
• Glia regulate the chemical content of extracellular space (astrocytes) and insulate neuron axons (oligodendrocytes and Schwann cells).
  • There are about 10 times more glial cells than neurons in the thalamus, midbrain, and brainstem.
  • There are about 1.5 times more glial cells than neurons in the cerebral cortex.
• Ependymal cells line fluid-filled ventricles and direct cell migration during brain development.
• Microglia eliminate debris from degenerating neurons and glia.
• Vasculature, including arteries, capillaries, and veins, supports blood supply in the brain.

Parts of a Prototypical Neuron

• Cell membrane: the boundary of the cell.
  • Lipid bilayer (two fat layers).
  • Contains proteins like receptors and channels.
• Dendrites: receive input from other neurons.
  • Part of synapses (post-synaptic connections between neurons)
• Axon: provides input to other neurons.
  • Axon hillock: site of action potential generation.
  • Axon terminal: part of synapses (pre-synaptic).
• Cell body (soma):
  • Gene expression and transcription (nucleus).
  • Protein synthesis (rough ER, ribosomes).
  • Protein sorting (smooth ER, Golgi apparatus).
  • Cellular respiration/energy (mitochondria).
  • Cytosol: fluid inside the cell.

Electrical Theory Basis

• Electric charge: positive or negative charge carried by electrons and protons.
  • Protons are positively charged, electrons are negatively charged.
  • The atom is positively charged if it has fewer electrons than protons.
  • The atom is negatively charged if it has more electrons than protons.
• Important ions for neuronal signals:
  • Positively charged metal ions: sodium (Na+), potassium (K+), calcium (Ca2+).
  • Negatively charged ions: chloride (Cl-).
• Electric field: surrounds positive and negative sources.
  • A positive ion moves toward a negative source.
  • A negative ion moves toward a positive source.
• Electrical potential: energy needed to move a positive ion towards a positive source of an electric field.
  • A positive ion has more stored energy near the positive source.
  • A positive ion loses potential energy as it moves towards a negative source.
  • Opposites attract, and like charges repel.
• Potential difference: difference in electric potential energy between two sites.
  • Measured in volts (V), which is energy per unit charge (J per coulomb).
  • Neuronal range is on the order of mV (e.g., 70mV).
• Current: movement of charged particles (e.g., Na+, K+).

Ion Concentration Gradient Across Cell Membrane

• The cell membrane separates ions but isn't permeable to them, maintaining different concentrations inside and outside the neuron.
• This difference creates a concentration gradient.
• Ions flow from high to low concentration sites through ion channels.
  • Ion channels selectively allow movement of particular ions through the membrane.

Membrane Potential

• The electrical potential difference between the inside and outside of a cell is called the membrane potential.
  • Reflects charge separation across the cell membrane (e.g., higher Na+ outside, higher K+ inside).
• Resting membrane potential: inside of the cell is more negative than outside.
  • Typically -65mV to -70mV when the cell is at rest.
• When channels open, ions move across the membrane based on electrical potential difference.
  • Positive ions move toward the negative compartment.
• Depolarization: membrane potential becomes less negative (more positive).
• Hyperpolarization: membrane potential becomes more negative.
• Two factors drive ions across the cell membrane:
  • Concentration gradient.
  • Electric potential difference (membrane potential).
  • Ions move toward their equilibrium potential (Eion), which balances the ionic concentration gradient.
  • K+ is key to resting membrane potential due to leaky potassium channels at rest, making the potential close to Ek+.
• Voltage-gated ion channels open or close in response to changes in membrane potential.
  • Charged protein subunits change conformation based on membrane potential (e.g., sodium and potassium channels).
• Ligand-gated ion channels: a type of membrane receptor that acts as a gate when the receptor changes shape.
  • Ligand = transmitter/messenger.
  • Examples: AMPA glutamate receptor (positive ion channel) and GABA receptor (chloride channel).
• Membrane potential threshold: Na+ channels open when the membrane depolarizes, generating an action potential (around -45mV).
  • Sodium moves into the cell, channels stay open briefly (1ms).
  • Channels cannot immediately reopen (1ms) - absolute refractory period.

Action Potential (Spike)

• A rapid reversal of the membrane potential momentarily makes the inside positive relative to the outside.
  • It's an all-or-nothing event (from -70mV to 30mV and back to -70mV).
• Carries information long distances along the axon to connected cells.
• After the absolute refractory period, more spikes can be generated if the cell depolarizes to the threshold.
• Ion currents change during each phase of the action potential.
  • Depolarizing phase: Na+ channels open, causing inward sodium current.
  • Hyperpolarizing phase: Na+ channels close, more potassium channels open, causing outward potassium current (resetting potential).
• Sodium-potassium pump re-establishes concentration gradients using ATP to transport Na+ and K+ across the membrane against their concentration gradients.
• Action potential propagation: generated at the axon hillock and propagates as a wave along the axon to the axon terminal (orthodromic direction).
  • Inward currents depolarize adjacent membrane sections, with a conduction velocity of approximately 10 m/s.
  • Action potentials can also travel toward the cell body (back propagation or antidromic direction).

Summary

• Cell membranes separate ions (more sodium outside, more potassium inside).
• Electrical potential differences exist across the cell membrane (resting membrane potential: inside more negative than outside).
• Action potentials are generated when a cell is depolarized to the threshold.
  • Sodium channels briefly open causing Na+ influx.
  • The membrane potential repolarizes when potassium channels open causing K+ efflux.
• Action potentials transmit along the axon to the next cell across the synapse.

Single-Neuron (Single-Unit) Recordings

• Intracellular recordings:
  • Record action potentials from the targeted cell.
  • Record subthreshold membrane potential fluctuations.
  • High spatial resolution.
• Extracellular recordings:
  • Record action potentials (spikes) from nearby cells.
  • Sort spikes based on shape to individual cells.
  • Record subthreshold fluctuations summed from nearby cells (Local Field Potentials - LFP).
  • LFP amplitude correlates with proximity to the cell.
  • Great spatial and temporal resolution is the gold standard.
• Local field potentials: extracellular subthreshold fluctuations summed from nearby cells reflect events in dendrites of local neuron populations.

Electrode Types:

• Classical electrode: has a few microns of metal exposed at the tip (used in extracellular recordings).
• Matrix electrode: connects 10 classical electrodes to measure neuron populations (used in extracellular recordings).
• Utah array: an array of electrodes (usually 10x10) implanted into the subject's brain (used in extracellular recordings).
• Laminar probe: has multiple electrode contacts to record neural activity; regular spacing allows observation of different activity in different cortical layers (used in extracellular recordings).
• Neuropixels probe: has 1000s of contacts to record 100s of neurons simultaneously, potentially representing a thought or concept.
• Smaller electrode contact or tip increases spatial resolution but also increases resistance:
  • A high resistance makes it harder for currents to flow through.

Electrode Impedance

• Impedance is a measure of resistance + electrode's ability to store charge (capacitance).
• Smaller electrode contact or tip increases impedance and resistance, allowing isolation of individual neuron spikes if within 10s of microns.
• Larger exposed metal contact has lower impedance and cannot isolate individual neurons.

Local Field Potential (LFP) Recordings:

• Extracellular depth electrode: records electrical potentials generated by about 1000 cells within 250 microns of the tip.
• Electrocorticography (ECoG):
  • Intracranial recordings from epilepsy patients to localize seizure activity.
  • Electrodes are placed on the exposed brain surface (subdural).
  • Signals mainly derived from superficial layers of the cerebral cortex.
• Electroencephalography (EEG):
  • Reflects activity of hundreds of thousands to millions of cells!
  • Smears the EEG signal, degrading source localization and causing poor spatial resolution.
  • Summation of synchronized activity of neurons with similar spatial orientation.
  • Predominantly derived from pyramidal cells in the cortex.
  • Electrodes are placed above the scalp (non-invasive).
  • Deep brain structures are inaccessible.
  • Good temporal resolution, following changes as quickly as they can be recorded (ms by ms).
  • EEG oscillations are rhythmic, with a fixed frequency.

Functional Magnetic Resonance Imaging (fMRI)

• A noninvasive imaging technique that uses magnetic fields to excite hydrogen atoms and map brain activity by measuring changes in blood flow and oxygen levels (BOLD signal = blood oxygen level dependent).
• Indirect measure of neural activity that reflects SUBTHRESHOLD MEMBRANE POTENTIALS (better correlated with LFP than with spikes).
• Good spatial resolution (2x2x2mm3; better than EEG).
• Poor temporal resolution (e.g., sampling every 2s) muddles cognitive operations.
• Voxels: small cube-shaped areas in the brain used in the analysis of fMRI data.
  • Typically 2x2x2mm3 or 3x3x3mm3 (~100,000 voxels per study).
  • Each voxel contains approximately 500,000 cells, with a signal change size of about 2%.

Neural Codes:

• Spike Rate Code: number of spikes in a given interval.
  • How the brain codes most information, with much evidence supporting rate coding.
  • Generally, increasing stimulus intensity increases the number of spikes (up to a point).
• Pooled Response Code: number of spikes from multiple cells in a given interval.
  • Combining activity from many cells reduces "noise" from the variability of individual cells.
  • Incorporates rate coding into population codes.
• Labeled-Line Code: vector formed from joint firing of multiple neurons.
  • Which neurons fire as well as the number of spikes is important.
  • (1,2) = 1 spike from cell 1, 2 spikes from cell 2.
• Spike Train: series of action potentials.
  • May have more information than just the number of spikes.
  • Spikes do not always re-occur after a fixed time.
  • Variability in spike timing could be useful information.

Spike Timing Codes (Temporal Codes):

• Spike Pattern Code: temporal pattern of spikes in a given interval.
  • Each interval is divided into smaller time bins, creating a binary code (0 or 1).
• Spike Phase Code: spike timing relative to the phase of oscillations.
  • Network oscillations provide a temporal reference frame or clock.

Neural Decoding:

• Encode: map a stimulus to a response.
• Decode: map a response to a stimulus.
• Pattern Classifier: algorithm using multivariate neural activity to predict the image category or class at the time of recording (houses vs. faces).
  • Dimensions could be spike rates of neurons or BOLD signals in voxels (fMRI).
• Two-step process for decoding:
  • Training step: using a subset of data to train a classifier.
    • The classifier learns the relationship between the pattern of neural activity and the experimental condition (category or class).
  • Test step: the classifier predicts the category of new data (face or house).
• Raster plots display spike rate at different sites.

Decoding Spike Rate:

• For N neurons and K images, each dot represents a spike rate from one image presentation.
• The training step uses red dots for a spider image and blue dots for the Tower of Pisa.
• The test step assigns new data (gray dot) to the class of its nearest neighbor (Tower of Pisa predicted).

Performance:

• Invasively, multi-unit activity (MUA) and LFP methods combined give the best performance; spikes and LFP can improve classification performance when decoding from multiple sites.
• LFP alone is the worst performer.
• MUA is slightly better than single-unit activity.
• Non-invasively, fMRI data is noisy, requiring averaging over many trials to get predicted voxel activity patterns.
  • Decoding fMRI data from a single image presentation significantly reduces accuracy.
  • Spiking data provides the most accurate information, but LFP, EEG, and fMRI (LFPs) still have some value.

Neural Prostheses

• Neural signals measured:
  • Spikes and LFP (invasive).
  • fMRI (non-invasive but not portable).
  • EEG (non-invasive and portable but reduced decoding accuracy).
• Requirements:
  • Stable long-term neural recordings from many neurons.
  • Efficient (real-time) computational data analysis.
  • Brain plasticity to incorporate feedback from an effector (e.g., brace).
• Development examples:
  • Intracranial implants (recording spikes and/or LFPs).
  • EEG-based devices.

Summary

• Neural codes fall into two main categories:
  • Spike rate code (number of spikes in a given interval).
  • Spike timing code (when spikes occur; spike pattern and spike phase code).
• Much evidence supports spike RATE coding in the brain.
  • Decoding based on spike rate can predict stimuli well.
  • General agreement that spike rate is an important neural code.
• Evidence that spike TIMING codes may also be used.
  • Spike timing information can improve decoding.
  • However, it is important to know whether the brain uses the information available in spike timing through causal data (directly manipulate spike timing and change behavior accordingly).
• Neural decoding and prostheses show how informative different neural codes are.
  • Ideally, to understand the brain, accurate predictions about its behavior, fix it when it is damaged, and build working models need to be made.

Brain Orientation:

• Anterior/Rostral: front of the brain.
• Posterior/Caudal: back of the brain.
• Dorsal: top of the brain.
• Ventral: bottom of the brain.
• Lateral: away from the midline of the brain.
• Medial: toward the midline of the brain.
• Sulcus: fissure.
• Gyrus: ridged portion of a convoluted brain surface.

Brain Areas:

• Temporal Lobe: receives auditory information and higher-level vision.
• Thalamus: sensory switchboard, first-order thalamic areas receive input directly from the sensory periphery (eye, ear, skin); relays messages to the cortex and transmits replies to the cerebellum and brainstem.
• Higher Order Cortical Areas: connect with primary areas (e.g., V4, secondary auditory areas to prefrontal association area); structural motif = more complex representations anteriorly.
• The eye sensory information pathway has more processing steps along the brainstem before reaching the thalamus compared to ear and skin pathways; the ears bypass the thalamus altogether.

Pathways:

• Feedforward Pathway: posterior to anterior cortical areas providing sensory environment information.
• Feedback Pathways: anterior to posterior, carrying information about goals, attention, and predictions.
  • Modulates neural activity in posterior areas (amplifies or filters).
• Direct Pathways: carry detailed information about sensory stimuli.
• Indirect Pathways: facilitate processing of behaviorally relevant information via the higher-order thalamus.

Cerebral Cortex

• Contains primary sensory areas, secondary sensory areas, and high-order areas.
• Low-level sensory information is represented in primary sensory areas.
• Higher-level information is represented in higher-order areas.

Role of Indirect Pathways:

• Filter or amplify information based on behavior.

Higher Order Thalamus:

• Limited sensory organ input but receives primarily from the cerebral cortex.
• What Pathway: occipital lobe to temporal lobe for perceiving and recognizing objects.
• How Pathway: primary visual cortex to parietal lobe; helps determines how to use objects and find them.

Structural Differences in the Cerebral Cortex:

• Neocortex has six layers (2-3mm thick), varying between brain areas. Cytoarchitectonics refers to neuron arrangement in the brain.
• Areas like the primary motor cortex (PMC) lack a layer 4/input layer/granular cortex.
• Columns and microcolumns repeat across the cortex.
• Columns are fundamental computational units.

Cell Types:

• Excitatory Cells: depolarize post-synaptic cells, including pyramidal cells found in layers 2, 3, 5, 6 in the cerebral cortex (70% of cells in cortex).
• Inhibitory Cells: hyperpolarize post-synaptic cells, like bi-tufted, double bouquet, small basket, large basket, and chandelier cells.
• Neurons can only operate on the information they receive, as not all cells connect.

Canonical Microcircuit:

• Layer 4 receives feedforward input from the thalamus or another cortical area.
• Layer 2/3 sends feedforward output to another cortical area.
• Layer 5 sends feedforward output to subcortical areas.
• Layer 6 sends feedback output to the thalamus or another cortical area (2/3).
• Layer 1 receives feedback input from another cortical area (and thalamus).

Brain Differences Across Species:

• The frontal lobe expands from mouse to macaque to humans; however, causal interventions and genetic modification aren't possible in humans, limiting research options compared to macaques and mice.
• Human prefrontal cortex exhibits granular (L4) cortex while rodents lack a granular frontal cortex.

Anatomical Structure Provides Insight into Function

• Cell level: considers whether the cell is excitatory or inhibitory, and the size/orientation of the dendritic field.
• Circuit level: considers lamination pattern or arrangement of cells, feedforward or feedback connections, and which connections are absent.
• Systems level: considers which brain areas are connected and whether connections are reciprocal or unidirectional.

Summary

• Information is processed in multiple stages: peripheral sensory organs, first-order thalamic areas, followed by primary and higher-order cortical areas.
• Direct and indirect pathways, via higher-order thalamus, feature feedforward and feedback routes; indirect allows us to filter out behaviorally irrelevant information.
• Horizontal layers and vertical columns/minicolumns structurally organize the cerebral cortex: Layer 4 receives feedforward input, layer 2/3 sends feedforward output, layer 5 sends feedforward output, layer 6 sends feedback output, layer 1 receives feedback input.

Basal Ganglia:

• Striatum = (putamen, caudate nucleus), subthalamic nucleus, substantia nigra, globus pallidus (external and internal segment).
• Contributes to action selection, reinforcement learning, and regulating information processing.
• Cortico-striatal-thalamic loops are used for limbic, associative, motor, and sensory functions.

Loops

• Cortex --> striatum --> globus pallidum/substantia nigra --> thalamus --> cortex
• One-way loops preferentially process certain types of information; most of the cerebral cortex projects to the striatum, except for the primary visual cortex and primary auditory cortex.
• Increased striatal activity can disinhibit/excites the thalamus via the direct pathway; the striatum inhibits the GP internal segment, which removes inhibition of the thalamus.
• Hyperdirect Pathway: cortex to subthalamic nucleus to reduce activity in the thalamus (inhibition); fewer connections and quicker to stop actions fast.
• Indirect Pathway: inhibits the thalamus to decrease cortical control of movement.
• Direct Pathway: disinhibits the thalamus to increase cortical control of movement.
• Cerebellum plays a role in more automatic execution; involved in both motor and cognitive functions; receives copies of commands from the motor and prefrontal cortex (called "efference copies").
• The cerebellum may output/predict sensory consequences, increasing predictability, efficiency, and real-time fine-tuning, bypassing sensory pathways.

Cortico-hippocampal circuits

• Neocortex parahippocampal areas (perirhinal cortex, entorhinal cortex) OR thalamus (higher order) then paraphippocampal areas them to hippocampus back to neocortex or thalamus (higher order)
• Episodic memory and spatial navigation.
• Recalling memories requires interaction between the cerebral cortex and hippocampus.

Small World Networks

• Many real-world networks are small worlds, e.g., movie actor networks. They may be regular, random, or a small-world network.
• Regular Network: connects each node to its nearest neighbor, offering high clustering but long path lengths.
• Random Network: increases disorder with random edge reconnections, offering long-range connections and rapid transmission, but giving up systematic local specialization.
• Small-world Network: combines high clustering with short characteristic path length.
• Module: a cluster of nodes with high within-module connectivity and low inter-module connectivity.
• Node Degree: the number of connections that link a node to the rest of the network.
• Path Length: the minimum number of edges to go from one node to another.
• Connector Hub: has high within and between-module connectivity.
• Provincial Hub: has high within and low between-module connectivity.
• Clustering Coefficient: the number of connections between nearest neighbors of a node.
• Rich-club Architecture: a type of small world network evident in the brain.
• Rich Node: a node with a large number of connections (a high-degree node/network hub).
• Rich Club: rich nodes that are well-connected with each other.
• The brain exhibits greater likelihood of high-degree nodes forming clubs, and it may cause the disruption of information transmittance if impaired.

Anatomical and Functional Connections

• Anatomical Connections: axon projects from one neuron to another; parallel axon projections form white matter paths.
• Functional Connections: correlated neural activity between different brain areas.
• Functional connections may reflect a direct or indirect anatomical path between brain areas.

Measuring Connections:

• Anatomical Connections measured by tracer studies (invasive) and diffusion MRI (non-invasive).
• Functional Connections measured by statistical dependencies (correlation, coherence)
• Resting state functional MRI.

Anatomical network hubs:

Precuneus, posterior cingulate cortex, superior frontal cortex, anterior cingulate cortex, insular cortex, lateral parietal cortex, and thalamus

Summary slide lecture 4 (brain networking)

• **cerebral cortex interacts with subcortical areas during cognition and action
• -cognition NOT restricted to the domain of the cerebral cortex (also thalamus, cerebellum, striatum, hippocampus)
• -basal ganglia: action selection and reinforcement learning
• -cerebellum: skill learning and automaticity
• -hippocampus: episodic memory and spatial navigation
• **brain networks can be defined using
• -anatomical connecitons
• -functional connections
• -similarity of anatomical and functional networks supports the idea that "neurons wired tg, fire tg"
• **brain exhibits small world properties:
• -high clustering
• -small characteristic path length between nodes
• **commonly identified brain hubs:
• -precuneus, cingulate cortex (PCC and ACC), superior frontal cortex, lateral parietal cortex, thalamus

Receptive field

The area from which information is received; the part of the sensory world to which the neuron responds; different receptive field sizes serve different purposes

• -> different receptive field sizes serve different purposes

Position invariance

Ability to identify an object no matter where it is (achieved in brain with multiple sensors with different receptor field sizes)

Brain Operation on Multiple Spatial Scales

• Localizing and identifying small objects. Identifying big objects or scenes. Identifying objects wherever they are (position invariance).
• -> representation of environment built from small receptive fields
• -> representation of our environment built from big receptive fields
• -> representation of environment built from different stimulus features, e.g., motion, color, etc.
• Brain builds recpetive fields of different sizes to perform better on multiple spatial scales:
  • small receptive fields usually found at early stages of sensory pathways near sensory organs
• -> bigger receptive fields can be built from small receptive fields
• -> if neurons with small, adjacent receptive fields all provide input to the same neuron, then summing these inputs will produce a bigger recpetive field

Somatosensory receptive fields

• Area of body surface
• Smallest RFs on finger tips
• Largest RFs on thigh/calf Mapped along dimensions of body surface

Visual receptive field

• Area of visual space
• Smallest RFs only a few minutes of arc (look like dot on page) (1/60th of a degree)
• Largest RFs tens of degrees (look like entire page of book)
• Mapped along (usually 2) dimensions of the space around you

Olfactory receptive field

Mapped along dimension of carbon chain length of odorant\

Numerical receptive field

Mapped along dimension of numerosity (like a number line)

Combining receptive Fields

Neurons with small, adjacent receptive fields sum inputs at the same neuron.

• representations of our environment at multiple scales, each has unique advantage
  • Small RFs = great Acuity; detailed features of an object

• Big RFs = position-invariant, can send feedback to lower level for detailed info, send information (feedforward signals) from RFs to the correct stimulus features (motion, color)

Topographic Maps in Brain

Brain areas commonly defined by their representation of sensory space

• Disproportionate representation of sensory word, where certain parts of the sensory space may occupy disproportionately large part of map (e.g., the fovea)
• Each distinct visual brain area (V1, V2, etc) contains a complete representation of half of a visual field (hemifield) contralateral to it (e.g. visual area in L hemisphere predominantly represents it)

Retinotopic map in V1

V1 in and around calcarine sulcus Mapping order from retina to cortex

Tonotopic maps in auditory brain area

Orderly representation of sound (tone) frequency

• -> neurons that prefer low frequency tones are more anterior

Somatosensory map in somatosensory brain area

Orderly representation of body surface with disproportionate space dedicated to hands, fingers, face

Advantages of multiple topographic maps

Efficient design to group neurons together that are highly interconnected If number of neurons in fine-grained maps is high, each neuron requires more connections (long-range)

• -> small RFs Fewer neurons in coarse-grained map facilitate comparison and integration from different parts of the map
• -> big RFs

summary lecture 5 (receptive fields and topographic maps)

• **neurons have receptive fields
• part of sensory world to which neuron responds
• **receptive fields can be described along different dimensions
• visual receptive field covers area of visual space
• somatosensory receptive field covers area of body surface
• **neurons commonly arranged in a topographic map:
• orderly representation of sensory world
• **multiple maps of sensory world in brain:
• much of brain organized according to topographic maps
• important for efficient wiring and coding

Reference frame

A coordinate system to represent the position of object

• -> origin of a coordinate system is particular, using reference point (lectern or car) -Egocentric and Allocentric

• 3 Egocentric = self-centered

• 2 Allocentric = world-centered (external stimuli)

• If i move the ret receptive field with me, then the info on screen can be represented in egocentric field ( in parallel)

Egocentric Examples - object related to self

• Eye, head, body centered

Allocentric Ex - where am I not withstanding

• Object-centered and workd-centered(map coordinates)

Allosteric Hippocampus

Sensory information - encodes info in egocentric

Pathway between parietal cortex and the hippocampus

• Transfers between the ego and all centered coordinates during navigation

Retrosplenial cortex involvement in transformations

Retrosplenial Cortex is Located with hippocampus and parietal cortex--> contains both allocentric and egocentric

Head Direction Cells

Found in the anterior thalamus--> they responds regardless if body movements influence the directional movements

Importance of Interacts Between the Parietal Cortex and Hippocampus

Limbic used for transformations betwixt ego and allow coordinates during navigation

• -> Parietal cortex and hippocampus needs to work in sequence with each other

• 3 types of coordinate systems in place in egocentric place systems

Transformations: travels to the body from eye centered

• -> how to use object and where is object located

Sensorimotor transformation seeing to grasping the target

• In order to move arm to the corresponding location, these steps have to occur...

• Visual target in eye-centered system Visual Cortex--> PPC--> BODY centered--> Body system-->M1--> MOVE Reaching for coffee: If all are equal T = eyesight of cup H - eye centered position

To Find Hand Centered Position:

1. Get T-H by substracting from eye-centered
2. Compute T-H by tracking eye placement to hand

• Eye-in-head placement to body placement--> leads to placing hand on body
• -> Parietal cortex is important for coordinate transformations using proprioceptors

summary slide lecture 6 (Coordinate systems and the brain's babel fish)

Reference frame: a coordinate system used to represent the position of an object, etc

Brain uses egocentric and allocentric reference frames

• egocentric: eye centered, body centered
• allocentric: object centered, world centered

Different brain areas use different reference frames:

• visual cortex uses eye-centered reference frame
• motor cortex uses body-centered reference frame
• hippocampus uses allocentric reference frame

Parietal cortex crucial for transformations between reference frames Transformations between eye-centered and body-centered coordinates Transformations between egocentric and allocentric coordinates? Synaptic transmission summary slide (lecture 7)--> the brain has ability to enhance with what we enhance our world with and diminish with little effort-Action potentials arriving at axon terminal of pre-synaptic neuron can trigger NT release-Transmitter diffuses across synaptic cleft and binds to receptors on post-synaptic neuron-Opening of transmitter-gated ion channels leads to post-synaptic potential

Two types of post synaptic potentials:

• Excitatory post synaptic potential (EPSP) produced by glutamate-Inhibitory post-synaptic potential (IPSP) produced by GABA
• increasing of the synaptic connections will enhance synapses!

Synaptic plasticity

• Long term potentiation is increased magnitude of EPSP after high pre-synaptic activity (e.g., using a pathway a lot)-Long term depression is decreased magnitude of EPSP after low pre-synaptic activity
• Calcium plays key role in transmitter release and synaptic plasticity:- Increased calcium triggers presynaptic actions with the membrane

Synapse

Connection of the neuronal synapse (pre & post)

Major Chemicals

Neurotransmitter (NT), receptor, and sub threshold potential are released across the membrane via post-synaptic potential

Axo, dendritic, somatic membrane synapse Synapse: synaptic cleft, synaptic vesicles, active & synaptic zones, the presynaptic zone Neurotransmitter Synthesis w/ Chemicals synthesized

• Synthesized w/amino acids, amines, and peptides

1. Synaptic Dock zone
2. Ap lead to calcium production
3. Calciums Trigger for Vesicles

Cell Membrane: Two classes of post synaptic receptors

Ligand gated ion channels (ionotropic) are opened by the fast actions of protein -channel receptors which has long cascade from the Gs

Transmission

Is fast acting compared to G - protein, which releases calcium and effects membrane potential positively or negatively

Drug Binding

Bind to Valium to influence how the drugs attach

Temporal Summation

A smooth vM Curve from synaptic signals The process happens as the potentials add together with a slight lag in time Synaptic plasticity - how effectively information is transmitted across memory- also changing the magnitude of the potential,

• Potentations & Synapses go between different scales 1 SHORT term 2 LONG term

LTP (Long Term Potentiation) occurs in several processes Protein KINASE Increase effect INSERT AMPA Receptors

How??--> high and low frequency = memory. LTP occurs only when neuron active Protein Phosphate occurs in 1 hz cycles

Declarative memories: semantic and epi Non - procedural classical and musculature in that case

H.M.-- temporal w damage = memory loss from a portion in time

• declarative= declarative memories = temporal cortex,

Hippocampal interactions

Is required during formation = consolidation and retrievval Is necessary during mem formation Spatial Navigation

2 Patterns of memory- Epsi

Pattern Seeker -- ability to distinguish b/w 2 ppl by memories and time periods

Role of memory in The Hippocampus

• Brain binds cortical inputs into integrated memory,
• -> hippocampus gives partial input, Model of interactions with neo

• Pattern Completion: full patterns recall the experience with a partial input!