MemoryGateway to Learning

Types of Memory• Declarative memory = Explicit memory

– Learning about people, places and things

• Nondeclarative memory = Implicit memory– Memory for skills or behavior

• Working memory temporary information storage – includes several types of information– probably from several sites in the brain

• Spatial memory – memory of location

• Relational memory – things that happen at same time get stored together

in a manner that ties them together

Explicit Memory• Learning about people, places and things

– Can be verbally reported– Requires conscious awareness

• Short-term memory – temporary, limited in capacity– requires continual rehearsal

• Long-term memory • more permanent, much greater capacity• does not require continual rehearsal • Consolidation

– transfer from short-term memory to long-term memory

Implicit Memory

• Procedural memory • Memory for skills or behavior • Perceptual and motor learning• Does not require conscious

awareness

Major Features of Memory

• Memory has stages• Long term memory is represented

in multiple regions of the CNS• Implicit and explicit memory

involve different neural circuits– Explicit requires the temporal lobe– Implicit involves the cerebellum,

amygdala

Memory is Not Unitary

• Memory is not an “all or none” phenomenon

• Can be implicit or explicit or a mixture

• Depends on how the information is stored and recalled

Amnesia - Loss of Memory• Dissociated amnesia

– not associated with any other cognitve deficits

• Retrograde amnesia – loss of memory for the time period before a trauma – typically is gradational from essentially complete loss

just before trauma to less and less complete loss earlier and earlier before trauma

• Anterograde amnesia– inability to form new memories

• Transient global amnesia – sudden, brief onset of anterograde amnesia

• The different types of amnesia suggest that several mechanisms for memory work together

Causes of Amnesia• Causes

– concussion, chronic alcoholism, encephalitis, brain tumor, stroke

• Transient amnesia– Probably caused by interruptions in cerebral

blood flow– Blows to head, physical stress, cold

showers, sex, drugs– Clioquinol (anti-diarrheal drug) - no longer

on market became famous for causing transient global amnesia in some people

Localization of Memory Functions

• Long thought memory was a function of the whole cerebral cortex

• We now realize that different types of memory are localized in different regions

• Engram – physical representation or location of

a memory

Cortical Ablation Studies • Karl Lashley – 1920s• Tried to localize memory engram to

association areas of the neocortex • Studied effect of brain lesions on ability to

learn a maze in rats– As more and more of the rat's cortex was

ablated, more and more errors were made– ability to learn was progressively impaired

• Lashley incorrectly concluded that the whole neocortex equally participated in memory – now know that the problem was that the lesions

were too large

Cell Assembly • Donald Hebb – 1949• The internal representation of an object consists of

the cortical cells that are activated by the stimulus– Group of simultaneously acting neurons = cell assembly – Same neurons are involved in sensation and perception– All of these cells are reciprocally interconnected

• Internal representation of an object remains in short term memory as long as the cell assembly is active

• If assembly active long enough, consolidation occurs– Long term memory– Neurons that fire together wire together– Activating any cells in the assembly activates the memory

• Led to neural network model                      

Localization of Declarative Memories

• Studies in macaque monkeys -  • Lesions in the inferotemporal cortex (IT)

cause loss of memory about previously learned visual discrimination tasks, even though vision itself remains normal – Cells in the IT may respond preferentially to a

familiar face in a particular orientation – Cells in IT may change their response during

repeated exposure to an unfamiliar face – learning

• The IT is involved both in vision and visual memory

Human Studies

• fMRI shows what part of the brain is activated during exposure to various types of objects – Bird watchers respond more

vigorously to pictures of birds – Car buffs respond more vigorously to

pictures of cars and responses are in different places

The Temporal Lobe• Wilder Penfield – 1940’s• Electrical stimulation of human temporal

lobe– Studied patients with epilepsy– During surgery for epilepsy, stimulated

temporal lobe electrically

• Some patients reported sensations like hallucinations or vivid memories– but the patients had other cortical

abnormalities– Still, temporal lobe stimulation caused

different effects than stimulation of other parts of the neocortex

• Consistant with seizure “aura”

Kluver-Bucy Syndrome• Researchers at U. Chicago in the 1930’s• Studying emotion circuitry• Bilateral temporal lobectomy in rhesus

monkeys• Produces bizarre behavioral

abnormnalities• One of these is “psychic blindness”

– Although they could see, could not recognize or understand the meaning of common objects

– Thus loss of declarative memory

• More on this phenomenon with emotion

Building on Penfield

• Brenda Milner – 1950’s– Studied patients with surgical

interventions to treat epilepsy– Bilateral removal of the hippocampus

and neighboring regions of the temporal lobe

• Most famous case was “H.M.”

Patient “H.M.” Sheds New Light

• Bilateral removal of mid-temporal lobe• Stopped seizures• Short term memory was OK• Memories formed prior to surgery were

OK• Ability to form new, long term memories

was lost– Couldn’t transfer information from short term

to long term memory!

• Similar findings in all bilateral temporal lobe surgical patients

Impact on Learning

• All of the things these patients could recall have an automatic quality– Do not require conscious recall– Do not require complex cognitive skills

such as comparison

• If the patient practices a puzzle, they improve their ability to solve it, but they don’t remember how.

Medial Temporal Lobe Anatomy

• Hippocampus – deep in the medial

temporal lobe• Entorhinal cortex,

perirhinal cortex, parahippocampal cortex – Three cortical

regions ventral to the hippocampus

– all involved in memory functions

Function of the Medial Temporal Lobe

• Lesions in monkeys impair discrimination memory– ability to recognize whether object has been

seen before

• Lesions impair declarative memory, not procedural memory

• Lesions impair long-term memory storage, but short-term memory seems to be normal

• This region seems to be involved in packaging short-term memory for relay to the rest of the neocortex for long-term storage

The Diencephalon & Memory• Outside of the temporal lobe, one of the

regions most associated with memory• Axons from the hippocampus project to the

mammillary bodies which project to the thalamus

• Thalamus also receives input from temporal lobe structures including the amygdala & IT

• Large midline thalamic lesions in monkeys produce severe deficits in ability to learn a matching task

• Lesions which impact fewer nuclei produce smaller deficits

The Diencephalon• Three regions have

been implicated in memory processing:– Anterior nucleus of

thalamus– Dorsomedial

nucleus of thalamus– Mammillary bodies

in hypothalamus• The thalamus &

mammillary bodies receive nerve fibers from the medial temporal lobe

The Case of “N.A.”• Accidentally stabbed with a fencing foil

– Through his right nostril into his brain

• Produced a lesion in his left dorsomedial thalamus

• Cognitive ability normal but memory impaired• Caused moderate retrograde amnesia (for the 2

years prior) and profound anterograde amnesia similar to the more extensive damage to H. M.

• Short term memory and preservation of old memories was intact

• Suggests that both the temporal lobe and parts of the thalamus may be involved in the formation of long-term declarative memories

Korsakoff's Syndrome • Usually due to chronic alcoholism• Results from alcohol associated thiamin deficiency• Produces confusion, severe memory impairment,

apathy• First presents as abnormal eye movements, loss of

coordination, tremors – Can be treated in early stages

• Untreated thiamin defiency leads to brain damage which produces Korsokoff’s– Lesions in dorsomedial thalamus and mammillary bodies

• Anterograde and severe retrograde amnesia• Further supports role of diencephalon in memory

Anterograde & Retrograde Amnesia

• While often found together, may have different causes

• The degree of severity of the two does not correlate in Korsokoff’s

• Suggests different mechanisms involved• Damage to the dorsomedial thalamus

and mammillary bodies probably causes anterograde amnesia

• What causes retrograde amnesia is still unclear

Working Memory & the Hippocampus

• Hippocampus is involved in memory function for a diverse range of tasks

• Studies of hippocampal ablation in rats• Studied “working memory”• Used a radial maze containing food

– Normal rats learn to visit each arm only once

– If only some arms are used, they learn only to go down those arms, and then only once.

The Maze Study• Rats with hippocampal

lesions still find the food, but they aren't very efficient, going down the same arm repeatedly

• Rats with lesions can learn to avoid the arms that never have food, but they still explore the food containing arms inefficiently and repeatedly

• Inability to use changing information

Place Cells in the Hippocampus

• Neurons in the hippocampus selectively respond when rat is in a particular location.

• If vision is used to determine place, (like landmarks) cell fires in response to where the animal thinks he is

• May be responsible for learning radial arm maze

• More than spatial memory is involved• Hippocampus may control relational

memory

Relational Memory• Highly processed sensory information

comes into the hippocampus & cortex• Processing occurs leading to the storage of

memories • All things happening at the same time are

stored together• Thus, remembering one thing brings back

related memories• It's easier to remember events that you had

strong feelings about.• Spatial navigation is based on a spatial map

& relational memories

Striatum and Procedural Memory

• Procedural memory = memory involved in forming behavioral habits

• Striatum is the major structure involved in procedural memory

• Striatum may be involved in forming 'habits' in rats, humans, & non-human primates

• Data from humans suggests that the striatum is involved in a procedural memory system that is separate and distinct from the medial temporal system used for declarative memory

Neocortex and Working Memory

• Humans have much more prefrontal cortex than any other animals

• Pathways: – Medial temporal lobe >> hypothalamus >>

anterior nucleus of thalamus >> cingulate cortex

– Medial temporal lobe >> dorsomedial nucleus of thalamus >> frontal cortex

• Experiments suggest that frontal cortex is involved with working memory for problem solving and planning of behavior

Frontal Lobe & Memory

• The left frontal lobe (colored regions at left) supports our ability to retrieve the meaning of words and objects.

Lateral Intraparietal Cortex (LIP)

• Cortex buried in intraparietal sulcus • Involved in working memory• Responses specific to vision • Example: monkey looks at fixation point

while a stimulus is flashed in periphery; after delay, monkey moves eyes to where the stimulus was

• Cells in LIP seem to store information about where the eyes are to be moved– they remain active during the delay - specific for

visual working memory

• There is a different area specific for auditory working memory

Many Structures are Involved in Memory

Summary – Memory Pathway #1

• Visual information is first routed through the thalamus to the visual area of the cerebral cortex.

• This neural activity is the basis for the sensory register

Summary – Memory Pathway #2

• Information is relayed to the frontal lobes where it is held in short term memory

Summary – Memory Pathway #3

• Information that is stored in long-term memory is held in the hippocampus for weeks or months, and then transferred to the area of the cerebral cortex near where it was originally process for long-term storage

Summary – Memory Pathway #4

• When we recall information from long term memory, it is routed again to the frontal lobes, where it is held in short-term, or “working” memory.