Cognitive psych: 9/10/26 lecture

The physiology of cognition

• Neuropsychology: Behavior of people with brain damage

• Electrophysiology: where we’re studying the electrical responses of the nervous system

• Cognitive neuroscience: Physiological basis of cognition

How to examine physiological basis of cognition

• Gross anatomic structure

• Central nervous system

• Brain region

• Cortical subregion

• Neural network

• Neuron

• Synapse

• ^But you don't have to look at ALL of these levels

Neurons:

Building blocks of the brain

• Send and receive information to each other; some neurons receive information from the environment

• Makes up a neuron: cell body (mechanisms for that cell’s survival, keeping the cell alive), dendrites (to receive information transmitted from other neurons, kinda look like tree branches), axons ( kinda looks similar to dendrites but with less branches, to send information), neural circuits (specific groups of neurons that tend to activate each other creating a circuit 

The synapse

• Gap or space between neurons and dendrite

• Specialized to send and receive information

• Receptors

• Neurotransmitters (each does something different)

How neurons communicate: Neurotransmitters at dendrites

• Dendrites receive neurotransmitter (NT) from other neurons, which can:

• Excite - makes the neuron more likely to fire (e.g., glutamate)

• Inhibit - makes the neuron less likely to fire (e.g., GABA)

• Modulate - temporarily changes how the neuron responds to other input (e.g., acetylcholine

How neurons communicate: Action Potentials (APs)

• If total excitation > threshold → an action potential (AP) is "fired."

• The nerve impulse (AP) travels down the axon to the axon terminals.

• Neurons are all-or-none - they either fire or they don't (the size of the AP does not change)

How neurons communicate: After an AP

• When the AP reaches the axon terminals, neurotransmitter is released to the next neuron.

• After each AP:

• Released NT is cleared/inactivated (e.g., reuptake or enzymatic breakdown).

• Brief refractory period - short time when the neuron cannot fire again (takes a break)

How neurons communicate: Coding Information

• Action potentials are measured by rate (frequency), not "size" (amplitude is constant).

• In sensory neurons (e.g., sight, sound), a higher firing rate indicates a stronger (more intense) stimulus

How neurons communicate: Neural Representation

• Different neurons respond to different stimuli (they are selective).

• Principle of Neural Representation:
  Everything we experience (e.g., sights, sounds, thoughts) is ultimately conveyed by patterns of neural activity (e.g., which neurons fire and how often)

If a drug were to block the release of a neurotransmitter where would this drug be working?

axon

Imagine a neuron's activity: Single cell recording

• Where we actually record the activity in individual neurons

• Have to put a recording device in a neuron (recording electrode inside axon and a reference electrode outside the axon)

• Typically done with animals, not done commonly on humans

• The recording can tell when the neuron fires

Representation in the Brain: Feature Detectors

• Maybe specific neurons respond only to specific stimuli?

• Hubel and weasel discovered neurons that respond best to stimuli of a particular orientation, movement, length, etc.

Experience-Dependent Plasticity

Definition: The brain changes and adapts based on experience and the environment.

Examples:

• Cats: Visual brain development changed depending on what they were exposed to.

• Rats: Enriched environments → more developed neurons & thicker cortex.

Representation by neurons: Types of sensory coding

Most representations are population or sparse

Localization: Subregion

• We can look at areas nor structures of the brain, not just individual neurons

• neuroimaging

EEG: ELECTROPENCEPHALOGRAPH

Neuron “firing” is an electrical event recorded by electrodes

– ERP (Event Related Potential) – momentary change in EEG signal

– Advantage: continuous, rapid measurements (good timing); easier

and cheaper to use

– Disadvantage: does not give precise location

fMRI: Functional magnetic resonance imaging

• Blood flow increases in areas activated by a cognitive task

-Oxygen content affects blood’s magnetic properties

- BOLD (blood oxygen level dependent) response for voxels is recorded by an electromagnetic system

-^v Advantage: good localization

- Disadvantage: Timing of activity is not as precise as EEG

Representation by subregion

• Activation patterns associated with a cognitive process

• A problem: anything that you do in the scanner makes much of the brain active; the brain never really “rests”

Subtraction Method

Purpose: Finds which brain activity is related to a specific cognitive process.

How it works: Compare two similar tasks and subtract the brain activity they share.

Example:

• Read real word “bread” → visual + phonemic decoding + lexical access

• Read non-word “blick” → visual + phonemic decoding

• Subtract → Lexical access

Task 2 − Task 1 = brain activation for the process you want to isolate.

Neuropsychology

Purpose: Figure out what a brain area does by studying brain damage.

How it works:

• Find a patient with brain damage + a specific problem.

• Identify where the damage is.

• Compare them to a healthy person doing the same task.

• See if the healthy person uses the same brain area that is damaged in the patient.

Damage to an area + loss of a function → that brain area is likely involved in that function.

Neuroimaging Methods: spatial resolution

-Ability to pinpoint where neural activity occur

- As high as 0.001 mm for single cell recording 

- As low as 5 cm for EEG

Neuroimaging Methods: temporal resolution

- Ability to pinpoint when neural activity occurs

- As fast as milliseconds for neural firing

- As slow as 4 or more seconds (fMRI) or even longer

Lobes of The Human Brain

Frontal is Front

• Parietal is at the Peak

• Temporal is behind the Temples

• Occipital lobe is Out back

Distributed Processing in the Brain

But….most of our experiences are multidimensional

• In addition to localization of function, functions are distributed (processed in many different areas)

• i.e., saying “language” is represented only in Broca and Wernicke’s areas, or facial processing only in the FFA, etc. is very incorrect

Neural Networks

Connected pathways that allow different brain areas to communicate and work together.

Two types:

• Structural connectivity = how brain areas are physically connected

• Functional connectivity = how brain areas work together

Structural = wiring
Functional = activity

Structural Connectivity + TWI (Track Weighted Imaging)

Structural connectivity: The brain's physical “wiring diagram.”

TWI (Track Weighted Imaging):

• Shows nerve fiber pathways/connections

• Uses water diffusion

• Shows structure, NOT brain activity/function

• Each person has a somewhat unique network

TWI = WHERE the brain is physically connected

Functional Connectivity

Functional connectivity: Shows which brain areas have correlated activity and work together.

• Think of it as a “functional diagram”

• Typically studied using resting-state fMRI

• Brain areas whose activity changes together are considered functionally connected

Functional connectivity = which areas WORK together

Resting State fMRI

Seed Location: reference area associated with a specific task

• Test Location: area where activity is measured, to determine degree of functional connectivity between it and seed location

Which technique gives the best spatial resolution for brain structures?

fMRI

Can neuroscience confirm an abstract behavioral construct?

Brain activation associated with a construct should not always be taken as proof of the psychological reality of the construct. You will find some locus of ANYTHING! Correlation ≠ Causation!