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Psyc 317: Cognitive Psychology. Lecture 2: Cognition & the Brain. Nervous system functioning: Outline. Zoom out: Broad anatomy of the brain Zoom in: Neurons How one neuron works How two neurons communicate How groups of neurons process information and encode the world

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Lecture 2: Cognition & the Brain

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Psyc 317: Cognitive Psychology

Lecture 2: Cognition & the Brain


Nervous system functioning: Outline

  • Zoom out: Broad anatomy of the brain

  • Zoom in: Neurons

    • How one neuron works

    • How two neurons communicate

    • How groups of neurons process information and encode the world

  • Zoom out again: Localization of function and basic principles of brain functioning


Neuron signals

  • Neurons are both chemical and electrical!

  • To send a signal within a neuron: ELECTRICAL

    • Action potentials

  • To send a signal between neurons: CHEMICAL

    • Neurotransmitters


Excitation/inhibition

  • Neurotransmitters come in two types

    • Excitation: Increase rate of firing of the nerve

    • Inhibition: Decrease the rate of firing of the nerve


Excitation/inhibition


Individual neurons respond to basic things

  • Cell that respond to stimuli can be classified:

    • Simple cells: ex. Bar oriented 45 degrees

    • Complex cells: ex. Bar oriented 45 degrees and moving to the right


Increasing complexity…

Individual cells get more and more complex…


Groups of neurons process more complex information

  • Neural circuits: Groups of interconnected neurons that interact to respond to stimuli

  • Often, many neurons connect to another

    • These neurons can be excitatory or inhibitory

    • Sum up activations together - exceed firing threshold?


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How neural circuits work

  • Example: Visual system

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Distributed coding

  • Complex things require multiple neurons and neuron groups to be activated in order to be identified

  • Recognizing objects requires more than just one neuron - network of cells that fire at different rates


How neurons encode objects

  • Grandmother cells? Not quite… distributed coding!


Distributed coding

  • It is through the distribution of firing rates ACROSS DIFFERENT NEURONS that an object is encoded


Nervous system functioning: Outline

  • Zoom out: Broad anatomy of the brain

  • Zoom in: Neurons

    • How one neuron works

    • How two neurons communicate

    • How groups of neurons process information and encode the world

  • Zoom out again: Localization of function and basic principles of brain functioning


Large groups of neurons are even more complex

  • Large groups of neurons form brain modules

    • Modules - Brains areas that are specialized for specific functions (memory, attention, etc.)

  • Localization of function - Different functions are found in different areas of the brain

    • Memory encoding is in the hippocampus

    • Attention is in the parietal lobe


Distributed activation

  • Big processes (like memory) require multiple functions - multiple groups of neurons

    • Emotions

    • Working memory

    • Long-term memory


How the brain encodes events

Distributed:

  • Form/shape

  • Color

  • Motion

  • Depth

  • Location


The brain is a multitasker


How the brain works: Contralaterality

  • The receptor and control centers for one side of the body are in the opposite hemisphere of the brain

    • Left hemisphere controls right side of body

    • Right hemisphere controls left side of body


How the brain works: Hemispheric Specialization

  • Different brain functions tend to rely more heavily on one hemisphere or the other

    • Example: The left hemisphere controls language for most right-handed people


Outline

  • Basics of information processing

  • Nervous system functioning

    • Broad anatomy

    • How neurons work

    • Localization of function

  • Methods of cognitive neuroscience

  • Experience-dependent plasticity


Introduction to Neuroimaging

  • Localization by methods that look at brain

    • Damage: If the hippocampus supports long-term memory (LTM), then hippocampal damage will interfere with LTM

    • Activation: If the hippocampus supports LTM, then when LTM is used, the hippocampus will be active


Techniques of activation

  • Single cell recordings

  • Event related potentials

  • Position emission tomography

  • Functional magnetic resonance imaging


Single cell recordings

  • Record from just one neuron in the brain

    • See how it reacts to stimuli

  • Mostly used in animals

  • Distinguish what one person is saying within a crowd of people

    • Still important to record from as many neurons as possible


Event-related potentials

  • Electrical response of thousands of neurons to a single event

    • Average electrical signal over hundreds of trials

  • Recorded through scalp cap


ERPs are part of the EEG

  • EEG is a way of continually recording brain waves

    • Common in sleep

      studies


How to collect ERPs

  • Give subject hundreds of trials of doing the same thing while recording the EEG

  • Mark the time in the EEG when something happens (stimulus, response, etc.)


How to collect ERPs

  • Save the EEG for (for example) 600 ms after that time marker for each trial

  • Average those EEG parts together to create an ERP waveform


ERP Waveforms

  • Positive and negative components

    • Waves go up and down

    • Each peak is a different component that often reflects cognitive processes


ERP: Good and Bad

  • Good: Excellent temporal resolution

    • Can detect changes in the ERP waveform very quickly

  • Bad: Poor spatial resolution

    • Averaging over millions of neurons - where does the signal come from? Who knows!


Brain imaging techniques

  • When neurons fire, they require oxygen.

  • Blood brings oxygen to the neurons

  • Positron Emission Tomography (PET)

    • Measure blood flow to brain using radioactive tracer

  • Functional Magnetic Resonance Imaging (fMRI)

    • Measure blood flow to brain using magnetic properties of deoxygenated blood


Functional MRI

Baseline

blood

oxygenation

Baseline firing

rate

Increased

blood

oxygenation

Increased firing

rate


fMRI scanner & images


Simple Reaction Time experiment:

Stimulus:

The light

Mind:

Sees light

Response:

Press button

Choice Reaction Time experiment:

*

Stimulus:

The light

Mind:

Sees light

Mind:

Which button?

Response:

Press button

Imaging & Subtraction

  • Subtraction technique

    • Like reaction time, but with brain imaging

    • (Experimental) - (Baseline)


Subtraction technique & imaging

  • How similar is seeing an object to visualizing it?


Imagery study: How would it work?

  • How similar is seeing an object to visualizing it?

  • Experiment with two conditions:

    • Actually seeing an object

    • Visualizing an object

  • Get brain scans for both conditions

  • What would you expect if there was no difference between visualizing and actually seeing?


fMRI: Good and Bad

  • Good: Excellent spatial resolution

    • Details of brain images can be accurate to several millimeters

  • Bad: Poor temporal resolution

    • Changes in blood flow take several seconds to occur - cannot pinpoint when something happened


Techniques of damage

  • Brain lesions that lead to dissociations

  • Transcranial magnetic stimulation (temporary “damage”)


Dissociations

  • Single Dissociation

    • A disruption in one cognitive process but no impairment of another

    • Just need one group with an impairment

  • Double Dissociation

    • Two patient populations with selective impairment to complimentary forms of a single task


Lesion studies

  • Problems with studying people with brain lesions?


Transcranial Magnetic Stimulation

  • High school physics…

    • Use moving magnet to create an electric field

  • A brief, changing magnetic pulse applied to the scalp of the participant

    • Creates an induced electrical field, which interferes with neuronal activity


Transcranial Magnetic Stimulation

  • This electrical field can either excite neurons or inhibit them

    • Excitation causes neurons to fire, making something happen

    • Inhibition causes neurons to decrease firing, making something stop happening


TMS procedure

Performance drop!

Prevent seeing the letter

Letter onset


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