Memory

• Working Memory

• Long term Memory– Deficits: HM, Alzheimer’s, Semantic Dementia

• Implicit Memory

Memory

Retrieval

Encoding

SensoryMemory

Short-termWorkingMemory

Long-termMemory

(knowledge)

20 secs

Implicit memory

200 ms‘Vision’

Working Memory

fMRI study of WM, showing distinct activation to faces and scenes

Working Memory & Long-term memory in a single task:

the Free Recall Task (& serial position function)

Subjects: - hear items (usually 10-40 words), then

- they say or write all the items they can remember, in any order.

Serial Position Function

Position in Original List

Probability of reporting

the item

1 2 ……… 30

?

1. Monster2. Camera3. Tricycle4. Melon5. Window6. Guest7. Quiet8. Cherish9. Waiting10. Rabbitt11. Computer12. Child13. Chicken14. Ghost15. Slave

RecencyPrimacy

STM contributionPrivileged rehearsalbetter LTM encoding

30 secs filled delayFaster presentation ratePatient HM

Declarative

SemanticMemory

EpisodicMemory

Types of Knowledge (long-term memory)

Procedural

This distinction emphasizes the kind of information represented (i.e. knowledge reported verbally vs motor skills).

Affected by Amnesia

2+2, sky is blue The Eagles won; ‘cook’ was a word in the list

Long-term Memory Systems

Explicit Memory

Implicit Memory

SemanticMemory

EpisodicMemory

Priming

ClassicalConditioning

Motor SkillLearning

Another Possible architecture of:

Affected by Amnesia

This emphasizes how information is accessed (conscious vs automatic)

2+2, sun is blue InstrumentalLearning

Anatomy of Explicit Memory

Mammillary body

Hippocampal formation

PosteriorParahippocampal cortex

Fornix

Mediotemporal Lobe (MTL)

Medial temporal lobe (MRI)

Folded shape

stained hippocampus 1. Hippocampus2. Perirhinal cortex

3. Posterior parahippocampal cortex

4. Amygdala

Mastering London Topography Changes Hippocampal Structure in Taxi Drivers (humans)

Bird species with good spatial memory have larger hippocampi

fMRI in normal subjects provide convergent evidence for the Role of hippocampus on episodic memory

Relational Memory

• What did you do at home last Wednesday?• A temporal context (last Wednesday)• A physical context (home)• A set of memory events (turkey, annoying parents,

tiredness, watching the game)

A relation between the events and the context (relational memory)

Amnesia

Bitemporal Lobectomy (patient HM)- treatment for epileptic seizures- It caused anterograde amnesia, but normal IQ, digit span, conversation, motor learning

Impaired Long-term Memory Encoding (chaplin vs. Britney spears;Old memories ok)

-Spared Working memory(digit span, recall)

-Spared Implicit memory- conceptual- perceptual- motor

Implicit memory:

Conceptual Priming in anterograde amnesia • Study phase: “is this word pleasant or not? “rape”, “love”, “sincere”, …..”

• Test phase:– Free Recall: Name the words on the list – Word Stem Completion: Complete “sco_ _ _”

• Impaired recall

but normal stem completion(i.e., as likely as normals to complete stems

with words that were observed earlier).

(Graf, Squire, & Mandler, 1984)

Implicit memory:Perceptual priming

Implicit memory motor: sequence learning task

implicit memory: rule learning

• Tower of Hanoi game– HM cannot remember playing, but solves

quickly.

Start Position Goal 2 (2 moves) Goal 10 (5 moves)

summary

• Medial Temporal Lobe amnesics– Explicit memory: unable to create

– Implicit memory: relatively intact

• So far: single dissociation– 2 possibilities:

1. Implicit/Explicit 2 independent systems

2. Implicit simply easier, relies on residual processing of a single, partially damaged system

– Double dissociation would support claim of 2 independent systems

• Patient MS– 29 year old, right handed male

– Intractable epilepsy: surgery removed right BA 17,18, part of 19.

– Hemianopic (blind in left field)

• Compared to MTL amnesics and healthy controls.

Gabrieli et al. (1995)

Explicit memory taskShown 24 words, later shown 48 words (24 from 1st phase, 24 new foils): asked to say if words were previously seen.Amnesics poor, visual lesion patient fine.

• Implicit memory: word completion task– Shown/Heard 24 words ‘stick’, later asked to complete 48 stems, 24 could be

solved with items from 1st phase (‘sti__’) and 24 unrelated stems (‘sta__’).– Healthy people show priming effect (faster if solution seen previously). This

effect is much bigger if words were seen (physical match) rather than heard.– Amensics show normal priming. Shows implicit memory.– MS visual priming is no greater than auditory priming. Therefore, shows no extra

benefit for physical match of stem and previously seen word.

ConclusionDouble dissociationExplicit memory has some distinct processing from implicit memory.‘Conceptual’ priming intact in MS, perceptual priming damaged

Anterograde Amnesia: causes

Fornix

Mammillary body

(Korsakoff Patients)

Hippocampal formation - HM

Other causes of amnesia include

– Chronic alcoholism (atrophy of mamillary body due to vitamin depletion, thiamin)

– Alzheimer’s disease (midtemporal atrophy)

– Electroconvulsive therapy

– Left frontal stroke (example)

Other causes of amnesia include

- Anoxia (CA1 atrophy)

Interestingly, a genetic mutation inactivating NMDA receptors in CA1 leads to:-Lack of Long-term potentiation-Poor spatial memory in the watermaze-Large & unfocused spatial receptive fields

Long-term Memory Systems

Explicit Memory

Implicit Memory

SemanticMemory

EpisodicMemory

Priming

ClassicalConditioning

Motor SkillLearning

2+2, sun is blue InstrumentalLearning

Semantic dementia: Loss of semantic memories caused by progressive degeneration of the neocortex of the left lateral temporal lobe.

• Graham et al. suggest double dissociation:– Early Alzheimer's patients

– ‘Semantic dementia’ patients

Alzheimers Patient

Hippocampus atrophy

Semantic Dementia

Temporal lobe atophy

Graham et al. 2000

B: Test stimuli

• A: Semantic naming task (‘phone’)– Correct answer: ‘phone’.

Memory tested 30 minutes later:

• B: Episodic memory task (perceptually identical)– Correct answer: ‘I saw a phone earlier’

• C: Episodic memory task (perceptually different)– Correct answer: ‘I saw a phone earlier’.

C: Semantic memory

• Semantic dementia patients have difficulty naming items.

• AD patients are fine at this task.

D: Episodic memory

• AD patients – poor episodic memory.

• SD patients – OK with identical items

– Poor with perceptually different (especially if unable to name item in picture naming phase).

E: Conclusions

• Suggests semantic and episodic memory may be separate.– Hippocampal formation: encoding episodic memories– Temporal lobe: storage of semantic memories.

– Additional support from Vargha-Khadem (1997), who reports 4 patients with selective hippocampal damage: all show impaired episodic but intact semantic memory.

• Note: all sustained hippocampal damage early in life, so does not necessarily generalize to adult brain.

Interaction of different brain regions

• Lesions in animals and functional imaging suggest network of regions work together to encode memory.

Spatial memory• Anatomy:

– Medial temporal lobe:• Hippocampus• Posterior parahippocampal area

• Evidence– Human Neuropsychology

• HM• London taxi drivers

– Animal research

Medial temporal lobe (MRI)

Folded shape

stained hippocampus 1. Hippocampus2. Perirhinal cortex

3. Posterior parahippocampal cortex

4. Amygdala

Mastering London Topography Changes Hippocampal Structure in Taxi Drivers (humans)

Bird species with good spatial memory have larger hippocampi

Spatial memory: Animal research

Spatial memory: Animal research

Place fields are stationary over time

Place cell:A neuron that becomes active when the animal is in a particular location in the environment; most typically found in the hippocampal formation (in dorsal hippoc, which is analogous to human post hippoc)

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Copyright © Allyn & Bacon 2007

Contextual informationSpatial alternation task (left, right, left)

SPARE SLIDES

From Patterson, 2007, NatNeuroRev

From Patterson, 2007, NatNeuroRev

From Patterson, 2007, NatNeuroRev

From Patterson, 2007, NatNeuroRev

54

Copyright © Allyn & Bacon 2007

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Copyright © Allyn & Bacon 2007

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Copyright © Allyn & Bacon 2007

Delayed non-match to sample

• Familiarity vs. explicit memory

Long-term Memory Systems

Explicit Memory

Implicit Memory

SemanticMemory

EpisodicMemory

Priming

ClassicalConditioning

Motor SkillLearning

InstrumentalLearning

Chapter 13: Single cell recording

Instrumental learning

Classical Conditioning (associative Learning)

What is the bases of such learning?Synaptic plasticity: “cells that fire together, wire together” (Donald Hebb)

Long-term potentiation: Following increased input there is a long-term increase in the excitability of the neuron that receives such input

Long-term potentiation in the rat hippocampus