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

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

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

Structure of a Neuron

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

Info Transmission: Simple Story Neurons are transducers – convert environmental energy to electrical energy (starting with receptors) 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 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 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 The neurotransmitters in the synapse trigger the same process (or a different one) in the next cell

Synapses

Info Transmission: Deeper Story Background concepts from physics Background concepts from physics Matter composed of molecules (always moving) Matter composed of molecules (always moving) Molecules can have +/- charge Molecules can have +/- charge Like charges repel, opposite charges attract Like charges repel, opposite charges attract

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 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

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 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 Depolarization phase: Sodium (Na+) Channels Repolarization phase: Potassium (K+) Channels Repolarization phase: Potassium (K+) Channels

Depolarization Phase

Depolarization + Repolarization

Info Transmission: Deeper Story Action potential moves down the axon, as gates open and close in sequence Action potential moves down the axon, as gates open and close in sequence

Synapses Action Potential reaches the end of the axon, triggering release of neurotransmitters 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)

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

Method: Single-Cell Recording Pictures of “spikes” – Pictures of “spikes” – keyword single cell recording keyword single cell recording Video clip from Hubel & Weisel (they got the 1981 Nobel Prize in physiology and medicine for this work) Video clip from Hubel & Weisel (they got the 1981 Nobel Prize in physiology and medicine for this work) keyword single-cell recording keyword single-cell recording

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

Value of Single-Cell Recording By itself, the data doesn’t tell us much By itself, the data doesn’t tell us much Can find cells that do almost anything Can find cells that do almost anything The value of single-cell recording for understanding human cognition depends on: The value of single-cell recording for understanding human cognition depends on: Functional organization of the brain Functional organization of the brain Consistencies of organization within species Consistencies of organization within species Meaningful mapping from animal models to organization of human brain Meaningful mapping from animal models to organization of human brain Fortunately, much evidence that these exist Fortunately, much evidence that these exist

Clarification from last time Question came up about diffusion and connection to neuron behavior Question came up about diffusion and connection to neuron behavior

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

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

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

Clarification from last time Things to note Things to note All action potentials are the same size, in terms of voltage (all-or-nothing principle) 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) 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.

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

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

Neurons as part of circuits Neural processing occurs when neurons synapse together to form a neural circuit Neural processing occurs when neurons synapse together to form a neural circuit Convergence Convergence Interaction of excitation and inhibition Interaction of excitation and inhibition

Neurons as part of circuits Neural processing occurs when neurons synapse together to form a neural circuit Neural processing occurs when neurons synapse together to form a neural circuit Convergence Convergence Interaction of excitation and inhibition Interaction of excitation and inhibition

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

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

Neural Codes in Daily Life Consider the case of recognizing the face of a specific person – how could that happen? 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 Hypothesis 1: specificity tuning – a particular neuron could selectively fire when you see that person

Specificity Coding Difficulties with Specificity Coding Hypothesis Difficulties with Specificity Coding Hypothesis Too many different faces, concepts, etc. to have a neuron for each one Too many different faces, concepts, etc. to have a neuron for each one Depends on experience – would have to learn each face (because neurons don’t reproduce) Depends on experience – would have to learn each face (because neurons don’t reproduce) Neurons selective for faces are active for many different faces Neurons selective for faces are active for many different faces Related idea: Grandmother cell (coined by Lettvin) Related idea: Grandmother cell (coined by Lettvin) Cell responds to image of a grandmother, general concept of grandmothers, your own grandmother 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 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 For recognition (and many other types of cognition), specificity coding is not enough

Neural Codes in Daily Life Hypothesis 2: Distibuted Coding – code for a specific face is distributed across a set of neurons Hypothesis 2: Distibuted Coding – code for a specific face is distributed across a set of neurons

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

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

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

Cerebral Cortex Most important for Cognition Most important for Cognition

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

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

Subcortical Structures

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

Hemispheres Brain separated into sides (hemispheres) Brain separated into sides (hemispheres) Corpus Collosum connects them Corpus Collosum connects them Structurally and functionally very similar Structurally and functionally very similar Lateralization – specific functions occurring in one hemisphere or the other 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 & Weisel’s Nobel Prize for this work.

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

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

Localized Function Parietal Lobe Parietal Lobe Sensory Homunculus (near the front, somatosensory cortex) Sensory Homunculus (near the front, somatosensory cortex) Motor Homunculus (near the back, motor cortex) Motor Homunculus (near the back, motor cortex) These guys aren’t actually IN your brain, they’re representations of how much cortex area is devoted to different body parts

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

Localized Function Parietal Lobe Parietal Lobe Sensory Homunculus (near the front, somatosensory cortex) Sensory Homunculus (near the front, somatosensory cortex) Motor Homunculus (near the back, motor cortex) Motor Homunculus (near the back, motor cortex) Temporal Lobe Temporal Lobe Wernicke’s Area – metaphor, meaning in language Wernicke’s Area – metaphor, meaning in language Broca’s Area – logical structure of language Broca’s Area – logical structure of language Fusiform Face Area (FFA) – specialized for faces (or is it things we’re experts at recognizing???) Fusiform Face Area (FFA) – specialized for faces (or is it things we’re experts at recognizing???)

Researching Localized Function Neuropsychology – comparing patients with localized brain damage Neuropsychology – comparing patients with localized brain damage Single dissociation– single patient has some things impaired, other things not impaired Single dissociation– single patient has some things impaired, other things not impaired

Single Dissociation: Phineas Gage Construction accident – 1848 Construction accident – 1848 Harlow (doctor) wrote a lot about his condition 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 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. Evidence for some separation of language and social traits, etc.

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

Double Dissociation Short-term memory Long-term memory Alice (temporal lobe damage) OKImpaired Bert (frontal lobe damage ImpairedOK

Double Dissociation Naming Living Things Naming Nonliving Things Group 1 (damage to area 1) OKImpaired Group 2 (damage to area 2) ImpairedOK

What can we conclude? Double dissociation Double dissociation Two functions involve different mechanisms Two functions involve different mechanisms Two functions involve different brain areas Two functions involve different brain areas Mechanisms are independent Mechanisms are independent Single dissociation Single dissociation Two functions involve different mechanisms Two functions involve different mechanisms Two functions involve different brain areas Two functions involve different brain areas Mechanisms may not be independent Mechanisms may not be independent

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

Imaging Methods EEG- Electrodes on outside of head continuously measure electrical activity 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 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) 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. 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 Temporal resolution: Detail with respect to time Spatial Resolution: Detail with respect to physiology Spatial Resolution: Detail with respect to physiology

Image from an fMRI scan Image from a PET scan

Imaging Methods Spatial Resolution Temporal Resolution EEGPoorGood PETExcellentPoor fMRIGoodGood TMSGoodGood

Subtraction Technique Used for fMRI studies Used for fMRI studies Method similar to Donder’s study Method similar to Donder’s study Compared two situations that included different cognitive processes Compared two situations that included different cognitive processes Data = blood glucose level Data = blood glucose level Relative measure Relative measure Visual Stimulus (light flashing) Perception of the light Response Visual Stimulus (light flashing) Perception of the light Response DECISION

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

Effects of experience Experience-dependant plasticity Experience-dependant plasticity Developmental environment can affect neuron specialization 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) 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 Learning happens through changes in connections and relationships between neurons, even in adulthood Greebles study (back to the FFA) Greebles study (back to the FFA)

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

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

Greebles Study Conclusions Conclusions Plasticity of FFA Plasticity of FFA FFA selects for things we’re experts about FFA selects for things we’re experts about Faces are things we’re experts about Faces are things we’re experts about