Memory and Memory and CognitionCognition
PSY 324PSY 324
Topic 2: Cognition and the Topic 2: Cognition and the BrainBrain
Dr. Ellen CampanaDr. Ellen Campana
Arizona State UniversityArizona State University
A BrainA Brain
Gray & White Gray & White MatterMatter
Solid tissueSolid tissue Made up of Made up of
neuronsneurons Golgi Golgi showed by showed by
staining slices staining slices with dyewith dye
NeuronsNeurons
Similarities with other cells of the bodySimilarities with other cells of the body Have a Have a nucleusnucleus containing DNA containing DNA Surrounded by a Surrounded by a cell membranecell membrane Contain mitochondria and other organellesContain mitochondria and other organelles Do basic cell stuff (protein synthesis, Do basic cell stuff (protein synthesis,
energy production)energy production) Unique characteristicsUnique characteristics
Do not reproduceDo not reproduce Structure, function, chemicals (details to Structure, function, chemicals (details to
come)come)
Structure of a NeuronStructure of a Neuron
Structure of a NeuronStructure of a Neuron
Varieties of neuronsVarieties of neurons
Function = transmit information to Function = transmit information to other cellsother cells Sensory / Afferent neuronsSensory / Afferent neurons: info : info
TOWARDTOWARD CNS CNS Motor / Efferent neurons: Motor / Efferent neurons: info info AWAY AWAY
fromfrom CNS CNS Interneurons: Interneurons: info to other neurons in info to other neurons in
the CNSthe CNS
Info Transmission: Info Transmission: Simple StorySimple Story
Neurons are Neurons are transducerstransducers – convert – convert environmental energy to electrical energy environmental energy to electrical energy (starting with (starting with receptorsreceptors))
Energy is Energy is propagatedpropagated from the from the dendritesdendrites into into the the cell body.cell body.
Energy is propagated to the end of the axon. Energy is propagated to the end of the axon. When it goes above a When it goes above a thresholdthreshold, it triggers the , it triggers the release of release of neurotransmittersneurotransmitters into the into the synapsesynapse
The neurotransmitters in the synapse trigger the The neurotransmitters in the synapse trigger the same process (or a different one) in the next cellsame process (or a different one) in the next cell
SynapsesSynapses
Info Transmission: Info Transmission: Deeper StoryDeeper Story
Background concepts from physicsBackground concepts from physics Matter composed of molecules (always Matter composed of molecules (always
moving)moving) Molecules can have +/- chargeMolecules can have +/- charge Like charges repel, opposite charges Like charges repel, opposite charges
attractattract
+ +- -+ -
Info Transmission: Info Transmission: Deeper StoryDeeper Story
Each neuron has a Each neuron has a resting resting potentialpotential, the voltage difference , the voltage difference across the cell membrane, caused by across the cell membrane, caused by the chemicals inside/outside the cell the chemicals inside/outside the cell when the cell is not firingwhen the cell is not firing
- --
-- -
--
--
++ +
+ ++ +
+
++ +
+ ++ +
+
Info Transmission: Info Transmission: Deeper StoryDeeper Story
Axon lined with Axon lined with ion channelsion channels (sodium channels, potassium (sodium channels, potassium channels) that open and close during channels) that open and close during an an action potentialaction potential to to propagatepropagate the signalthe signal Depolarization phase: Depolarization phase: Sodium (Na+) Sodium (Na+)
ChannelsChannels Repolarization phase: Repolarization phase: Potassium (K+) Potassium (K+)
ChannelsChannels
Depolarization PhaseDepolarization Phase
Depolarization + Depolarization + RepolarizationRepolarization
Info Transmission: Info Transmission: Deeper StoryDeeper Story
Action potentialAction potential moves down the moves down the axon, as gates open and close in axon, as gates open and close in sequencesequence
SynapsesSynapses
Action PotentialAction Potential reaches the end reaches the end of the axon, triggering release of of the axon, triggering release of neurotransmittersneurotransmitters
•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 Method: Single-Cell RecordingRecording
It is possible to record activity of a single It is possible to record activity of a single cellcell
Tiny wires (called Tiny wires (called microelectrodesmicroelectrodes) stuck ) stuck into into axonaxon, attached to , attached to oscilloscopeoscilloscope for data for data displaydisplay
Time is a factorTime is a factor De/Repolarization cycle = 1/1000 S or 1 msDe/Repolarization cycle = 1/1000 S or 1 ms Activities of cognition take at least 100ms – at Activities of cognition take at least 100ms – at
that resolution action potentials show up as that resolution action potentials show up as spikesspikes
Often most useful to talk about Often most useful to talk about firing rate firing rate
Method: Single-Cell Method: Single-Cell RecordingRecording
Pictures of “spikes” – Pictures of “spikes” – http://viperlib.york.ac.uk/ , keyword , keyword
single cell recordingsingle cell recording Video clip from Video clip from Hubel & WeiselHubel & Weisel
(they got the (they got the 1981 Nobel Prize1981 Nobel Prize in in physiology and medicine for this physiology and medicine for this work)work) http://viperlib.york.ac.uk/ , keyword , keyword
single-cell recordingsingle-cell recording
History of Single-Cell History of Single-Cell RecordingRecording
Participants in experiments:Participants in experiments: 1880s – People injured by accident with 1880s – People injured by accident with
exposed brains, also patients with epilepsyexposed brains, also patients with epilepsy 1950s – Fully anesthetized animals (cats, 1950s – Fully anesthetized animals (cats,
squirrels, monkeys, apes)squirrels, monkeys, apes) 1980s – Awake, active monkeys and apes1980s – Awake, active monkeys and apes
Invasive, destructive procedureInvasive, destructive procedure Data: there is a cell in the [animal] that Data: there is a cell in the [animal] that
increases firing under [conditions]increases firing under [conditions]
Value of Single-Cell Value of Single-Cell RecordingRecording
By itself, the data doesn’t tell us muchBy itself, the data doesn’t tell us much Can find cells that do almost anythingCan find cells that do almost anything
The value of single-cell recording for The value of single-cell recording for understanding human cognition depends understanding human cognition depends on:on: Functional organizationFunctional organization of the brain of the brain Consistencies of organization within speciesConsistencies of organization within species Meaningful mapping from animal models to Meaningful mapping from animal models to
organization of human brainorganization of human brain Fortunately, much evidence that these Fortunately, much evidence that these
existexist
Clarification from last Clarification from last timetime
Question came up about diffusion Question came up about diffusion and connection to neuron behaviorand connection to neuron behavior
Clarification from last Clarification from last timetime
Background concepts from physicsBackground concepts from physics Matter composed of molecules (always Matter composed of molecules (always
moving)moving) Molecules can have +/- chargeMolecules can have +/- charge Like charges repel, opposite charges Like charges repel, opposite charges
attractattract
+ +- -+ -
Clarification from last Clarification from last timetime
Background concepts from physicsBackground concepts from physics Matter composed of molecules (always moving)Matter composed of molecules (always moving) Molecules can have +/- chargeMolecules can have +/- charge Like charges repel, opposite charges attractLike charges repel, opposite charges attract
Cell membrane maintains an imbalance Cell membrane maintains an imbalance At rest, negative inside and positive outside At rest, negative inside and positive outside
(pumps maintain)(pumps maintain) Ion channels open / close quicklyIon 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 Sodium and Potassium are +, but other chemicals
create the negativity inside the axon at rest create the negativity inside the axon at rest Focus on Sodium and Potassium because of the Focus on Sodium and Potassium because of the
gatesgates
Clarification from last Clarification from last timetime
- --
-- -
--
--
++ +
+ ++ +
+
++ +
+ ++ +
+
AxonCell membrane (imbalance)Diffusion and charge drive the process – cells rush in/outThere are mechanical pumps but they just restore resting potential at the end
Clarification from last Clarification from last timetime
Things to noteThings to note All action potentials are the same size, All action potentials are the same size,
in terms of voltage (all-or-nothing in terms of voltage (all-or-nothing principle)principle)
Most useful to think of them as on / off, Most useful to think of them as on / off, or to think about firing rates (spikes per or to think about firing rates (spikes per second)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?Why study neurons?
Everything we see, hear, do, smell, Everything we see, hear, do, smell, remember, taste, touch, pay attention remember, taste, touch, pay attention to, and think about is to, and think about is represented represented physiologicallyphysiologically by neurons firingby neurons firing All sensations, perceptions and thoughts All sensations, perceptions and thoughts
are neural activationare neural activation All of our actions arise from neural signalsAll of our actions arise from neural signals
Study of cognition is about both Study of cognition is about both physiologicaphysiological and l and functional modelsfunctional models Increasingly uses brain imaging and Increasingly uses brain imaging and
neuroscience methods (later today)neuroscience methods (later today)
Brain OrganizationBrain Organization
Hierarchical StructureHierarchical Structure Smallest unit: NeuronSmallest unit: Neuron Neurons form Circuits (many levels)Neurons form Circuits (many levels)
Convergence, Inhibition, ExcitationConvergence, Inhibition, Excitation Related circuits contribute to localized Related circuits contribute to localized
functionfunction Brain areas for different functionsBrain areas for different functions Hemispheric specializationHemispheric specialization
Neurons as part of Neurons as part of circuitscircuits
Neural processingNeural processing occurs when neurons occurs when neurons synapse together to form a synapse together to form a neural circuitneural circuit ConvergenceConvergence Interaction ofInteraction of excitation excitation and and inhibitioninhibition
Neurons as part of Neurons as part of circuitscircuits
Neural processingNeural processing occurs when neurons occurs when neurons synapse together to form a synapse together to form a neural circuitneural circuit ConvergenceConvergence Interaction ofInteraction of excitation excitation and and inhibitioninhibition
Hubel & WeiselHubel & Weisel Single-cell recording of Single-cell recording of feature feature
detectorsdetectors Simple neuronsSimple neurons (from the video last (from the video last
time)time) Orientation (thickness, location of line)Orientation (thickness, location of line)
Complex neuronsComplex neurons Orientation, direction of motionOrientation, direction of motion
End-stoppedEnd-stopped Length, direction of motionLength, direction of motion
Feature DetectorsFeature Detectors
Lines (shapes and orientations)Lines (shapes and orientations) Directed MotionDirected Motion Complex StimuliComplex Stimuli
Geometrical figuresGeometrical figures Common objects in the environment Common objects in the environment
(houses, man-made objects, birds)(houses, man-made objects, birds) FacesFaces
Depend on Depend on selectivityselectivity – neurons – neurons firing at some times and not at othersfiring at some times and not at others
Neural Codes in Daily Neural Codes in Daily LifeLife
Consider the case of recognizing the Consider the case of recognizing the face of a specific person – how could face of a specific person – how could that happen?that happen?
Hypothesis 1: Hypothesis 1: specificity tuningspecificity tuning – a – a particular neuron could selectively fire particular neuron could selectively fire when you see that personwhen you see that person
Specificity CodingSpecificity Coding Difficulties with Specificity Coding HypothesisDifficulties with Specificity Coding Hypothesis
Too many different faces, concepts, etc. to have a Too many different faces, concepts, etc. to have a neuron for each oneneuron for each one
Depends on experience – would have to learn each Depends on experience – would have to learn each face (because neurons don’t reproduce)face (because neurons don’t reproduce)
Neurons selective for faces are active for many Neurons selective for faces are active for many different facesdifferent faces
Related idea: Related idea: Grandmother cellGrandmother cell (coined by (coined by LettvinLettvin)) Cell responds to image of a grandmother, general Cell responds to image of a grandmother, general
concept of grandmothers, your own grandmotherconcept of grandmothers, your own grandmother Some evidence that these might exist in Some evidence that these might exist in
Hippocampus – associated with memory storage, Hippocampus – associated with memory storage, not visionnot vision
For recognition (and many other types of For recognition (and many other types of cognition), specificity coding is not enoughcognition), specificity coding is not enough
Neural Codes in Daily Neural Codes in Daily LifeLife
Hypothesis 2: Hypothesis 2: Distibuted CodingDistibuted Coding – – code for a specific face is distributed code for a specific face is distributed across a set of neuronsacross a set of neurons
Distributed CodingDistributed Coding
AdvantagesAdvantages Efficient -- firing of fewer neurons can Efficient -- firing of fewer neurons can
represent many more different stimulirepresent many more different stimuli Similar items can have similar neural Similar items can have similar neural
codescodes Helps with learning Helps with learning
Graceful degradationGraceful degradation -- if one or two -- if one or two neurons do not fire, it is still possible to neurons do not fire, it is still possible to recognize a facerecognize a face
Reconciling types of Reconciling types of codingcoding
Evidence for Specificity Coding Evidence for Specificity Coding Feature detectorsFeature detectors Concept cells in hippocampus (memory area)Concept cells in hippocampus (memory area)
Argument for Distributed Coding in Argument for Distributed Coding in recognitionrecognition Clear theoretical advantages in recognitionClear theoretical advantages in recognition Will see a lot of evidence laterWill see a lot of evidence later
Both are happening in the brain – in different Both are happening in the brain – in different areas at the same time (areas at the same time (parallel parallel processingprocessing)) Pattern across (+ interaction btwn) Pattern across (+ interaction btwn)
areas=cognitionareas=cognition
The Whole BrainThe Whole Brain
Localization of functionLocalization of function - Different - Different parts of the brain serve different parts of the brain serve different functionsfunctions
Many, many ways to divide the brainMany, many ways to divide the brain Like an onion, many layersLike an onion, many layers Like a fractal, the closer you look the Like a fractal, the closer you look the
more complex it seems more complex it seems Descriptions may seem contradictory Descriptions may seem contradictory
and/or overlapping because of thisand/or overlapping because of this
Cerebral CortexCerebral Cortex Most important for CognitionMost important for Cognition
Cerebral CortexCerebral Cortex
Temporal Lobe Temporal Lobe LanguageLanguage MemoryMemory HearingHearing Perceiving formsPerceiving forms
Occipital LobeOccipital Lobe Visual information (early processing) – Visual information (early processing) –
feature detectorsfeature detectors
Cerebral CortexCerebral Cortex Parietal LobeParietal Lobe
TouchTouch VisionVision AttentionAttention
Frontal Lobe Frontal Lobe Proportionately larger in humans than Proportionately larger in humans than
in other speciesin other species LanguageLanguage ThoughtThought MemoryMemory Motor functioningMotor functioning
Subcortical StructuresSubcortical Structures
Subcortical StructuresSubcortical Structures
HippocampusHippocampus Forming memoriesForming memories
AmygdalaAmygdala Emotions, emotional memoriesEmotions, emotional memories
ThalamusThalamus Processing sensory information (vision, Processing sensory information (vision,
hearing, touch)hearing, touch)
HemispheresHemispheres
Brain separated into sides (hemispheres)Brain separated into sides (hemispheres) Corpus CollosumCorpus Collosum connects them connects them
Structurally and Structurally and functionally very functionally very similarsimilar
LateralizationLateralization – – specific functions specific functions occurring in one occurring in one hemisphere or the hemisphere or the otherother
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.
LateralizationLateralization
Vision of left part of the world Vision of left part of the world lateralized to the right side (opposite lateralized to the right side (opposite also true)also true)
Motor Control of left side of body Motor Control of left side of body lateralized to the right side (opposite lateralized to the right side (opposite also true)also true)
Touch on left side of body lateralized Touch on left side of body lateralized to the right side (opposite also true)to the right side (opposite also true)
LateralizationLateralization Are there “right-brained” and “left-Are there “right-brained” and “left-
brained” people?brained” people? Analytical/Logical processing (syntax of Analytical/Logical processing (syntax of
language) usually on the left side (not always)language) usually on the left side (not always) Analogy and Broad Thinking usually on the Analogy and Broad Thinking usually on the
right side (not always)right side (not always) Everyone has (and uses) bothEveryone has (and uses) both Patients who have had a Patients who have had a
hemispherectomyhemispherectomy Other side usually takes over missing Other side usually takes over missing
functionalityfunctionality Coglab “Brain Assymetry” Coglab “Brain Assymetry”
Localized FunctionLocalized Function
Parietal LobeParietal Lobe Sensory HomunculusSensory Homunculus (near the front, (near the front,
somatosensory cortexsomatosensory cortex)) Motor HomunculusMotor Homunculus (near the back, (near the back,
motor cortexmotor cortex))
These guys aren’t actually IN your brain, they’re representations of how much cortex area is devoted to different body parts
Sensory HomunculusSensory Homunculus
Each side of the brain has a
copy, which processes
touch from the other side
Localized FunctionLocalized Function
Parietal LobeParietal Lobe Sensory HomunculusSensory Homunculus (near the front, (near the front,
somatosensory cortexsomatosensory cortex)) Motor HomunculusMotor Homunculus (near the back, (near the back,
motor cortexmotor cortex)) Temporal LobeTemporal Lobe
Wernicke’s AreaWernicke’s Area – metaphor, meaning – metaphor, meaning in languagein language
Broca’s AreaBroca’s Area – logical structure of – logical structure of languagelanguage
Fusiform Face Area (FFA)Fusiform Face Area (FFA) – – specialized for faces (or is it things specialized for faces (or is it things we’re experts at recognizing???)we’re experts at recognizing???)
Researching Localized Researching Localized FunctionFunction
NeuropsychologyNeuropsychology – comparing – comparing patients with localized brain damagepatients with localized brain damage Single dissociationSingle dissociation– single patient has – single patient has
some things impaired, other things not some things impaired, other things not impairedimpaired
Single Dissociation: Single Dissociation: Phineas GagePhineas Gage
Construction Construction accident – 1848accident – 1848
Harlow (doctor) Harlow (doctor) wrote a lot about wrote a lot about his conditionhis condition Gage lived, could talk, act, and do Gage lived, could talk, act, and do
all “normal” activities, but suffered all “normal” activities, but suffered impairment of emotional, social, and impairment of emotional, social, and personal traitspersonal traits
Evidence for some separation of Evidence for some separation of language and social traits, etc. language and social traits, etc.
Researching Localized Researching Localized FunctionFunction
NeuropsychologyNeuropsychology – comparing – comparing patients with localized brain damagepatients with localized brain damage Single dissociationSingle dissociation – single patient has – single patient has
some things impaired, other things not some things impaired, other things not impairedimpaired
Alice: Short-Term Memory OK, Long-Term Alice: Short-Term Memory OK, Long-Term Memory impaired (like in Memento)Memory impaired (like in Memento)
Double dissociationDouble dissociation -- two (or more) -- two (or more) patients show opposite single impairmentspatients show opposite single impairments
Bert: Long-Term Memory OK, Short-Term Bert: Long-Term Memory OK, Short-Term Memory impairedMemory impaired
Double DissociationDouble Dissociation
Short-term Short-term memorymemory
Long-term Long-term memorymemory
Alice Alice (temporal (temporal lobe damage)lobe damage)
OKOK ImpairedImpaired
Bert (frontal Bert (frontal lobe damagelobe damage
ImpairedImpaired OKOK
Double DissociationDouble Dissociation
Naming Naming Living ThingsLiving Things
Naming Naming Nonliving Nonliving ThingsThings
Group 1 Group 1
(damage to (damage to area 1)area 1)
OKOK ImpairedImpaired
Group 2Group 2
(damage to (damage to area 2)area 2)
ImpairedImpaired OKOK
What can we conclude?What can we conclude?
Double dissociationDouble dissociation Two functions involve different mechanismsTwo functions involve different mechanisms Two functions involve different brain areasTwo functions involve different brain areas Mechanisms Mechanisms areare independent independent
Single dissociationSingle dissociation Two functions involve different mechanismsTwo functions involve different mechanisms Two functions involve different brain areasTwo functions involve different brain areas Mechanisms Mechanisms may not bemay not be independent independent
Limitations of Limitations of NeuropsychologyNeuropsychology
At least for human processing, brain At least for human processing, brain damage comes about from natural means damage comes about from natural means (accident, etc.)(accident, etc.) Members of groups rarely have exactly the Members of groups rarely have exactly the
same damage (location or extent)same damage (location or extent) No record of processing or brain organization No record of processing or brain organization
before the damagebefore the damage Difficult to assess all possible types of Difficult to assess all possible types of
functional impairment functional impairment Damage may cause reorganization Damage may cause reorganization
((plasticityplasticity))
Imaging MethodsImaging Methods EEGEEG- Electrodes on outside of head continuously - Electrodes on outside of head continuously
measure electrical activitymeasure electrical activity PETPET- Radioactive dye injected, accumulates in - Radioactive dye injected, accumulates in
different regions over time and can be read by a different regions over time and can be read by a scanner. Essentially measures metabolism of neuronsscanner. Essentially measures metabolism of neurons
fMRIfMRI- Brief magnetic pulses used to give a snapshot - Brief magnetic pulses used to give a snapshot of ratio of oxygenated to deoxygenated blood of ratio of oxygenated to deoxygenated blood (metabolism)(metabolism)
TMSTMS- New measure. Magnetic field can disable - New measure. Magnetic field can disable specific portions of the brain for a short time, specific portions of the brain for a short time, simulating damage.simulating damage.
Temporal resolutionTemporal resolution: Detail with respect to time: Detail with respect to time Spatial ResolutionSpatial Resolution: Detail with respect to physiology: Detail with respect to physiology
Image from an
fMRI scanImage from a
PET scan
Imaging MethodsImaging Methods
Spatial Spatial ResolutionResolution
Temporal Temporal ResolutionResolution
EEGEEG PoorPoor GoodGood
PETPET ExcellentExcellent PoorPoor
fMRIfMRI GoodGood GoodGood
TMSTMS GoodGood GoodGood
Subtraction TechniqueSubtraction Technique
Used for fMRI studiesUsed for fMRI studies Method similar to Method similar to
Donder’s studyDonder’s study Compared two Compared two
situations that situations that included different included different cognitive processescognitive processes Data = blood glucose Data = blood glucose
levellevel Relative measureRelative measure
Visual Stimulus (light flashing)
Perception of the light
Response
Visual Stimulus (light flashing)
Perception of the light
Response
DECISION
Subtraction TechniqueSubtraction Technique Activation in Activation in
control control condition is condition is subtracted from subtracted from experimental experimental condition to get condition to get activity due to activity due to stimulation in stimulation in the the experimental experimental conditioncondition
Effects of experienceEffects of experience
Experience-dependant plasticityExperience-dependant plasticity Developmental environment can affect Developmental environment can affect
neuron specializationneuron specialization Kittens raised in environment with only Kittens raised in environment with only
vertical lines had more of their brain devoted vertical lines had more of their brain devoted to recognizing vertical lines in adulthood (and to recognizing vertical lines in adulthood (and none devoted to horizontal)none devoted to horizontal)
Learning happens through changes in Learning happens through changes in connections and relationships between connections and relationships between neurons, even in adulthoodneurons, even in adulthood Greebles study (back to the FFA)Greebles study (back to the FFA)
GreeblesGreebles
Recall discussion of localization of Recall discussion of localization of functionfunction Fusiform Face Area (FFA) was an area in the Fusiform Face Area (FFA) was an area in the
Temporal lobe devoted to recognizing faces… Temporal lobe devoted to recognizing faces… or was it things we’re experts at or was it things we’re experts at recognizing??? recognizing???
Kanwisher has demonstrated, using fMRI, Kanwisher has demonstrated, using fMRI, that the area does selectively respond to facesthat the area does selectively respond to faces
Gauthier and colleagues showed fMRI Gauthier and colleagues showed fMRI evidence for experience-based plasticity in evidence for experience-based plasticity in this area (Greebles study)this area (Greebles study)
Greebles StudyGreebles Study Step 1: measure brain Step 1: measure brain
activity in FFA when viewing activity in FFA when viewing GreeblesGreebles
Step 2: train people to Step 2: train people to recognize individual Greebles recognize individual Greebles and families of Greeblesand families of Greebles
Step 3: measure brain Step 3: measure brain activity in FFA when viewing activity in FFA when viewing Greebles Greebles
Analysis: compare activity in Analysis: compare activity in FFA before and after trainingFFA before and after training
Greebles StudyGreebles Study
ConclusionsConclusions Plasticity of Plasticity of
FFAFFA FFA selects for FFA selects for
things we’re things we’re experts aboutexperts about
Faces are Faces are things we’re things we’re experts aboutexperts about
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