L&M Lecture 2-3_ Neuroscience PDF

8/27/2024 Neuroscience Neurons ○ Neurons: cells in the nervous system that are specialized for information processing ○ Simple units that serve as the building blocks of mental representations ○ Pass information via electrical and chemical signals...

8/27/2024 Neuroscience Neurons ○ Neurons: cells in the nervous system that are specialized for information processing ○ Simple units that serve as the building blocks of mental representations ○ Pass information via electrical and chemical signals ○ Function is determined by patterns of connectivity to other neurons (inputs and outputs) ○ Dendrites: collect signals from other neurons ○ Cell body: integrates signals ○ Axon: sends output to other neurons ○ Myelin sheath: transmits action potential ○ Axon terminals: synaptic information ○ Synapse: point where signal passes from one neuron to another ○ Input signals are gathered via dendritic connections (received from axons of other neurons) Inputs can be either excitatory or inhibitory ○ If enough excitatory input is received, an action potential is triggered: an electrical signal is sent down the axon (neuron fires) Action potential is an all or none (binary) response ○ Synaptic transmission (using chemical neurotransmitters) passes the signal to dendrites of other neurons Neural networks ○ When excitatory input is received from only 1 presynaptic neuron, not enough to trigger an action potential in the postsynaptic neuron ○ When lots of excitatory input is received from many presynaptic neurons, an action potential is triggered in the postsynaptic neuron and the signal is passed on ○ The flow of information among neurons can be represented using a network diagram, where each circle represents a single neuron ○ Input to integration to output Organization of the brain ○ Mapping the organization of the brain helps inform theories of learning and memory Functional specialization: the extent to which parts of the brain are dedicated to separate functions Dissociations in brain function provide evidence for multiple memory systems that operate in parallel Patient H.M. ○ Henry Molasion (1926-2008) ○ Suffered from epilepsy  ○ In 1953 (age 27) had surgery to remove bilateral medial temporal lobes (including most of hippocampus and amygdala) ○ Successfully reduced frequency of epileptic seizures, but also led to severe amnesia ○ Anterograde amnesia: a severe loss of the ability to form new episodic and semantic memories ○ Retrograde amnesia: loss of memories for events dating from before a brain injury or disruption Memory loss generally occurs in temporally-graded manner so that more recent memories are lost but older ones may be spared ○ Removal of medial temporal lobes led to H.M. experiencing both retrograde and anterograde amnesia ○ H.M. was a groundbreaking case because of the selectivity of his impairments ○ After the surgery, H.M. had Generalized declarative memory impairments regardless of materials (words, drawings, faces, etc.) Preserved memory for what he had known 2+ years prior Preserved ability to interact, converse, solve problems, perform tasks, but would forget those experiences within moments Preserved ability to learn new motor skills or form implicit memories Structural neuroimaging ○ Structural neuroimaging: obtain a snapshot of the anatomical structure within the brain Magnetic resonance imaging (MRI) Diffusion tensor imaging (DTI) ○ Cross sectional: compare anatomical structure in particular regions between different groups (patients vs. healthy controls) ○ Longitudinal: with repeated scans, track changes in anatomical structure over time (as a result of experience, aging, disease, etc.) ○ London taxi drivers must pass difficult test showing they have learned the layout of the city ○ Maguire used structural neuroimaging to compare the volume of brain areas to non-experts (non taxi drivers) ○ Larger volume in the posterior hippocampus which was correlated with length of time as a taxi driver Functional neuroimaging ○ Functional neuroimaging: record real-time changes in brain activity (via blood flow)  ○Compare activity in a region between different tasks (perceiving vs remembering an image) Summary ○ Neurons are basic units of information processing in the brain Function of a neuron depends on pattern of connection with other neurons Represent information processing using network diagrams ○ The brain is organized into regions which are specialized for different functions ○ Research in cognitive neuroscience links brain function to behavior, including learning and memory 8/29/2024 Neuroscience Part 2 Label the four lobes Testing memory: recognition vs recall ○ Recognition: do you remember experiencing the same event or object in the past? Can test recognition for an event from a particular context ○ Recall: given a retrieval cue, can you retrieve other details about an event or object from memory? Testing memory: recognition ○ In visual memory, a new event involves linking together low level visual features Seeing a new face which involves a unique combination of facial features ○ A particular combination of low level features creates a novel representation in memory ○ Recognition occurs when that representation (combination of features) is reactivated ○ When familiar features aren’t combined in the right way, you get uncanny valley Mapping the brain: receptive fields ○ Receptive field: the range (or field) of physical stimuli that activates a single neuron ○ Example: neurons in primary visual cortex selectively respond to lines that appear in a particular orientation Mapping the brain: distributed representations ○ Mental representation of a visual object involves layers of increasingly complex or abstract features as information flows through visual system ○ In V1, neurons selectively respond to line segments ○ In V4, neurons selectively respond to complex shapes  Hebbian learning and pattern completion ○ Donald Hebb Developed a theory of associative learning and memory in The Organization of Behavior Mental representations are constructed through synaptic plasticity in neural networks ○ Hebbian learning: learning the involves strengthening connections between neurons that fire together ○ Cell assembly: a group of interconnected neurons that operate as a functional unit Allows for pattern completion: activation of one component causes activation of the whole assembly Synaptic plasticity ○ Activity-dependent modification of the strength or efficacy of synaptic transmission ○ Long term potentiation: a process in which synaptic transmission becomes more effective as a result of recent activity ○ Long term depression: a process in which synaptic transmission becomes less effective as a result of recent activity Long term potentiation ○ Repeated stimulation of a presynaptic neuron causes firing of a postsynaptic neuron ○ For several hours afterward, larger response by the postsynaptic neuron to a single stimulation (postsynaptic neuron is potentiated) ○ LTP is a fast acting mechanism for the strengthening of the connection between two neurons ○ Two important properties: Specificity: the effect is specific to presynaptic neurons that caused the postsynaptic neuron to fire Associativity: LTP also occurs for other weaker inputs that occur at the same time, even if on their own they are not strong enough to cause the postsynaptic neuron to fire Long term depression ○ A process in which synaptic transmission becomes less effective as a result of recent activity ○ Occurs when there’s a mismatch between presynaptic and postsynaptic firing (the postsynaptic neuron fires in the absence of input from the presynaptic neuron)