Memory and Cognition

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Memory and Cognition

• PSY 324
• Topic 2 Cognition and the Brain
• Dr. Ellen Campana
• Arizona State University

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A Brain

• Gray White Matter
• Solid tissue
• Made up of neurons
• Golgi showed by staining slices with dye

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Neurons

• Similarities with other cells of the body
• Have a nucleus containing DNA
• Surrounded by a cell membrane
• Contain mitochondria and other organelles
• Do basic cell stuff (protein synthesis, energy
  production)
• Unique characteristics
• Do not reproduce
• Structure, function, chemicals (details to come)

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Structure of a Neuron
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Structure of a Neuron
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Varieties of neurons

• Function transmit information to other cells
• Sensory / Afferent neurons info TOWARD CNS
• Motor / Efferent neurons info AWAY from CNS
• Interneurons info to other neurons in the CNS

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Info Transmission Simple Story

• Neurons are transducers convert environmental
  energy to electrical energy (starting with
  receptors)
• Energy is propagated from the dendrites into the
  cell body.
• Energy is propagated to the end of the axon. When
  it goes above a threshold, it triggers the
  release of neurotransmitters into the synapse
• The neurotransmitters in the synapse trigger the
  same process (or a different one) in the next cell

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Synapses
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Info Transmission Deeper Story

• Background concepts from physics
• Matter composed of molecules (always moving)
• Molecules can have /- charge
• Like charges repel, opposite charges attract

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Info Transmission Deeper Story

• Each neuron has a resting potential, the voltage
  difference across the cell membrane, caused by
  the chemicals inside/outside the cell when the
  cell is not firing

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Info Transmission Deeper Story

• Axon lined with ion channels (sodium channels,
  potassium channels) that open and close during an
  action potential to propagate the signal
• Depolarization phase Sodium (Na) Channels
• Repolarization phase Potassium (K) Channels

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Depolarization Phase
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Depolarization Repolarization
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Info Transmission Deeper Story

• Action potential moves down the axon, as gates
  open and close in sequence

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Synapses

• Action Potential reaches the end of the axon,
  triggering release of neurotransmitters

• Excitatory neurotransmitters increase firing rate
  in next neuron
• Inhibitory neurotransmitters decrease firing rate
  in next neuron
• NOTE Other neurotransmitters do other things
  (less well understood, less relevant to
  cognition, especially to models we will talk
  about)

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Method Single-Cell Recording

• It is possible to record activity of a single
  cell
• Tiny wires (called microelectrodes) stuck into
  axon, attached to oscilloscope for data display
• Time is a factor
• De/Repolarization cycle 1/1000 S or 1 ms
• Activities of cognition take at least 100ms at
  that resolution action potentials show up as
  spikes
• Often most useful to talk about firing rate

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Method Single-Cell Recording

• Pictures of spikes
• http//viperlib.york.ac.uk/ , keyword single cell
  recording
• Video clip from Hubel Weisel (they got the 1981
  Nobel Prize in physiology and medicine for this
  work)
• http//viperlib.york.ac.uk/ , keyword single-cell
  recording

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History of Single-Cell Recording

• Participants in experiments
• 1880s People injured by accident with exposed
  brains, also patients with epilepsy
• 1950s Fully anesthetized animals (cats,
  squirrels, monkeys, apes)
• 1980s Awake, active monkeys and apes
• Invasive, destructive procedure
• Data there is a cell in the animal that
  increases firing under conditions

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Value of Single-Cell Recording

• By itself, the data doesnt tell us much
• Can find cells that do almost anything
• The value of single-cell recording for
  understanding human cognition depends on
• Functional organization of the brain
• Consistencies of organization within species
• Meaningful mapping from animal models to
  organization of human brain
• Fortunately, much evidence that these exist

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Clarification from last time

• Question came up about diffusion and connection
  to neuron behavior

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Clarification from last time

• Background concepts from physics
• Matter composed of molecules (always moving)
• Molecules can have /- charge
• Like charges repel, opposite charges attract

-
-

-
22
Clarification from last time

• Background concepts from physics
• Matter composed of molecules (always moving)
• Molecules can have /- charge
• Like charges repel, opposite charges attract
• Cell membrane maintains an imbalance
• At rest, negative inside and positive outside
  (pumps maintain)
• Ion channels open / close quickly
• Particles rush in / out (like a hole in a boat)
• Sodium and Potassium are , but other chemicals
  create the negativity inside the axon at rest
• Focus on Sodium and Potassium because of the gates

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Clarification from last time
Axon Cell membrane (imbalance) Diffusion and
charge drive the process cells rush
in/out There are mechanical pumps but they just
restore resting potential at the end
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Clarification from last time

• Things to note
• All action potentials are the same size, in terms
  of voltage (all-or-nothing principle)
• Most useful to think of them as on / off, or to
  think about firing rates (spikes per second)

These are from a specific study. Neuron A
responds when the stimulus is ON. Neuron B
responds when the stimulus is OFF. Neuron C
responds to changes in the stimulus.
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Why study neurons?

• Everything we see, hear, do, smell, remember,
  taste, touch, pay attention to, and think about
  is represented physiologically by neurons firing
• All sensations, perceptions and thoughts are
  neural activation
• All of our actions arise from neural signals
• Study of cognition is about both physiological
  and functional models
• Increasingly uses brain imaging and neuroscience
  methods (later today)

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Brain Organization

• Hierarchical Structure
• Smallest unit Neuron
• Neurons form Circuits (many levels)
• Convergence, Inhibition, Excitation
• Related circuits contribute to localized function
• Brain areas for different functions
• Hemispheric specialization

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Neurons as part of circuits

• Neural processing occurs when neurons synapse
  together to form a neural circuit
• Convergence
• Interaction of excitation and inhibition

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Neurons as part of circuits

• Neural processing occurs when neurons synapse
  together to form a neural circuit
• Convergence
• Interaction of excitation and inhibition

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Hubel Weisel

• Single-cell recording of feature detectors
• Simple neurons (from the video last time)
• Orientation (thickness, location of line)
• Complex neurons
• Orientation, direction of motion
• End-stopped
• Length, direction of motion

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Feature Detectors

• Lines (shapes and orientations)
• Directed Motion
• Complex Stimuli
• Geometrical figures
• Common objects in the environment (houses,
  man-made objects, birds)
• Faces
• Depend on selectivity neurons firing at some
  times and not at others

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Neural Codes in Daily Life

• Consider the case of recognizing the face of a
  specific person how could that happen?
• Hypothesis 1 specificity tuning a particular
  neuron could selectively fire when you see that
  person

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Specificity Coding

• Difficulties with Specificity Coding Hypothesis
• Too many different faces, concepts, etc. to have
  a neuron for each one
• Depends on experience would have to learn each
  face (because neurons dont reproduce)
• Neurons selective for faces are active for many
  different faces
• Related idea Grandmother cell (coined by
  Lettvin)
• Cell responds to image of a grandmother, general
  concept of grandmothers, your own grandmother
• Some evidence that these might exist in
  Hippocampus associated with memory storage, not
  vision
• For recognition (and many other types of
  cognition), specificity coding is not enough

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Neural Codes in Daily Life

• Hypothesis 2 Distibuted Coding code for a
  specific face is distributed across a set of
  neurons

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Distributed Coding

• Advantages
• Efficient -- firing of fewer neurons can
  represent many more different stimuli
• Similar items can have similar neural codes
• Helps with learning
• Graceful degradation -- if one or two neurons do
  not fire, it is still possible to recognize a
  face

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Reconciling types of coding

• Evidence for Specificity Coding
• Feature detectors
• Concept cells in hippocampus (memory area)
• Argument for Distributed Coding in recognition
• Clear theoretical advantages in recognition
• Will see a lot of evidence later
• Both are happening in the brain in different
  areas at the same time (parallel processing)
• Pattern across ( interaction btwn)
  areascognition

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The Whole Brain

• Localization of function - Different parts of the
  brain serve different functions
• Many, many ways to divide the brain
• Like an onion, many layers
• Like a fractal, the closer you look the more
  complex it seems
• Descriptions may seem contradictory and/or
  overlapping because of this

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Cerebral Cortex

• Most important for Cognition

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Cerebral Cortex

• Temporal Lobe
• Language
• Memory
• Hearing
• Perceiving forms
• Occipital Lobe
• Visual information (early processing) feature
  detectors

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Cerebral Cortex

• Parietal Lobe
• Touch
• Vision
• Attention
• Frontal Lobe
• Proportionately larger in humans than in other
  species
• Language
• Thought
• Memory
• Motor functioning

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Subcortical Structures
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Subcortical Structures

• Hippocampus
• Forming memories
• Amygdala
• Emotions, emotional memories
• Thalamus
• Processing sensory information (vision, hearing,
  touch)

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Hemispheres

• Brain separated into sides (hemispheres)
• Corpus Collosum connects them

• Structurally and functionally very similar
• Lateralization specific functions occurring in
  one hemisphere or the other

Note Sperry studied split-brain patients, who
had had their corpus collosum severed as a
treatment for epilepsy. He shared Hubel
Weisels Nobel Prize for this work.
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Lateralization

• Vision of left part of the world lateralized to
  the right side (opposite also true)
• Motor Control of left side of body lateralized to
  the right side (opposite also true)
• Touch on left side of body lateralized to the
  right side (opposite also true)

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Lateralization

• Are there right-brained and left-brained
  people?
• Analytical/Logical processing (syntax of
  language) usually on the left side (not always)
• Analogy and Broad Thinking usually on the right
  side (not always)
• Everyone has (and uses) both
• Patients who have had a hemispherectomy
• Other side usually takes over missing
  functionality
• Coglab Brain Assymetry

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Localized Function

• Parietal Lobe
• Sensory Homunculus (near the front, somatosensory
  cortex)
• Motor Homunculus (near the back, motor cortex)

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Sensory Homunculus
Each side of the brain has a copy, which
processes touch from the other side
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Localized Function

• Parietal Lobe
• Sensory Homunculus (near the front, somatosensory
  cortex)
• Motor Homunculus (near the back, motor cortex)
• Temporal Lobe
• Wernickes Area metaphor, meaning in language
• Brocas Area logical structure of language
• Fusiform Face Area (FFA) specialized for faces
  (or is it things were experts at recognizing???)

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Researching Localized Function

• Neuropsychology comparing patients with
  localized brain damage
• Single dissociation single patient has some
  things impaired, other things not impaired

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Single Dissociation Phineas Gage

• Construction accident 1848
• Harlow (doctor) wrote a lot about his condition

• Gage lived, could talk, act, and do all normal
  activities, but suffered impairment of emotional,
  social, and personal traits
• Evidence for some separation of language and
  social traits, etc.

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Researching Localized Function

• Neuropsychology comparing patients with
  localized brain damage
• Single dissociation single patient has some
  things impaired, other things not impaired
• Alice Short-Term Memory OK, Long-Term Memory
  impaired (like in Memento)
• Double dissociation -- two (or more) patients
  show opposite single impairments
• Bert Long-Term Memory OK, Short-Term Memory
  impaired

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Double Dissociation
Short-term memory Long-term memory
Alice (temporal lobe damage) OK Impaired
Bert (frontal lobe damage Impaired OK
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Double Dissociation
Naming Living Things Naming Nonliving Things
Group 1 (damage to area 1) OK Impaired
Group 2 (damage to area 2) Impaired OK
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What can we conclude?

• Double dissociation
• Two functions involve different mechanisms
• Two functions involve different brain areas
• Mechanisms are independent
• Single dissociation
• Two functions involve different mechanisms
• Two functions involve different brain areas
• Mechanisms may not be independent

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Limitations of Neuropsychology

• At least for human processing, brain damage comes
  about from natural means (accident, etc.)
• Members of groups rarely have exactly the same
  damage (location or extent)
• No record of processing or brain organization
  before the damage
• Difficult to assess all possible types of
  functional impairment
• Damage may cause reorganization (plasticity)

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Imaging Methods

• EEG- Electrodes on outside of head continuously
  measure electrical activity
• PET- Radioactive dye injected, accumulates in
  different regions over time and can be read by a
  scanner. Essentially measures metabolism of
  neurons
• fMRI- Brief magnetic pulses used to give a
  snapshot of ratio of oxygenated to deoxygenated
  blood (metabolism)
• TMS- New measure. Magnetic field can disable
  specific portions of the brain for a short time,
  simulating damage.
• Temporal resolution Detail with respect to time
• Spatial Resolution Detail with respect to
  physiology

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Image from an fMRI scan
Image from a PET scan
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Imaging Methods
Spatial Resolution Temporal Resolution
EEG Poor Good
PET Excellent Poor
fMRI Good Good
TMS Good Good
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Subtraction Technique
Visual Stimulus (light flashing)
Visual Stimulus (light flashing)

• Used for fMRI studies
• Method similar to Donders study
• Compared two situations that included different
  cognitive processes
• Data blood glucose level
• Relative measure

Perception of the light
Perception of the light
DECISION
Response
Response
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Subtraction Technique

• Activation in control condition is subtracted
  from experimental condition to get activity due
  to stimulation in the experimental condition

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Effects of experience

• Experience-dependant plasticity
• Developmental environment can affect neuron
  specialization
• Kittens raised in environment with only vertical
  lines had more of their brain devoted to
  recognizing vertical lines in adulthood (and none
  devoted to horizontal)
• Learning happens through changes in connections
  and relationships between neurons, even in
  adulthood
• Greebles study (back to the FFA)

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Greebles

• Recall discussion of localization of function
• Fusiform Face Area (FFA) was an area in the
  Temporal lobe devoted to recognizing faces or
  was it things were experts at recognizing???
• Kanwisher has demonstrated, using fMRI, that the
  area does selectively respond to faces
• Gauthier and colleagues showed fMRI evidence for
  experience-based plasticity in this area
  (Greebles study)

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Greebles Study

• Step 1 measure brain activity in FFA when
  viewing Greebles
• Step 2 train people to recognize individual
  Greebles and families of Greebles
• Step 3 measure brain activity in FFA when
  viewing Greebles
• Analysis compare activity in FFA before and
  after training

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Greebles Study

• Conclusions
• Plasticity of FFA
• FFA selects for things were experts about
• Faces are things were experts about