Disorders of Memory

David GroomIntroduction to Cognitive Psychology

Chapter 7

Anterograde Amnesia

• Impairment of memory since onset of amnesia.

• Failure of encoding (learning)Tests

Retrograde Amnesia

Impairment of memory for events occurring before the onset of amnesia.Temporal gradient (Ribot’s Law) Remote memories tend to be preserved, whereas recent memories are lost.

Found in most types of organic amnesia

Focal AA and RA

• In general, both AA and RA are found in organic amnesia.

• Rare cases in which there is only AA or only RA• Focal AA damage is confined to Anterior

Thalamus. • Focal RA damage to temporal lobe

Organic Amnesia

- Several Causes (share hippocampal damage)- Difficulty consolidating new memories (AA)- Generally some difficulty retrieving past

memories (RA)- Intact STWM (able to carry on conversations)- Normal digit span (7 items) and recency effect.- Irreversible

Areas of Brain that play a role in AA

Temporal Lobes

Hippocampus

Diencephalon

A cluster of subcortical structures in the center of the brain. For memory, the most important are the thalamus and the mammillary bodies.

Areas of the Brain that play a role in RA

Prefrontal Cortex

Temporal Cortex (Cortical areas that include the hippocampus)

Extended Hippocampal complex

- Thalamus, Mammillary bodies (Diencephalon) and Hippocampus.

- Encoding and Consolidation

Alzheimer’se.g., Ronald Reagan

• Degenerative Disorder - slow decline in memory, thinking and reasoning skills.

Ten Signs• Memory loss that disrupts daily life• Challenges in planning or solving problems• Difficulty completing familiar tasks at home, at

work or at leisure• Confusion with time or place

• Trouble understanding visual images and spatial relationships

• New problems with words in speaking or writing

• Misplacing things and losing the ability to retrace steps

• Decreased or poor judgment• Withdrawal from work or social activities• Changes in mood and personality

Korsakoff’s Syndrome

Lack of vitamin B1 - common in people with alcoholism. - malabsorption disorders- chronic illness or after bariatric surgery.- AIDS, Long-term dialysis or of intravenous (IV)

therapy-Extreme nausea vomiting (e.g., during pregnancy)

Symptoms of Korsakoff’s syndrome:

• Inability to form new memories• Loss of memory, can be severe• Temporal gradient - the more remote the event in the

past, the better it is preserved and the sharper the recollection of it.

• “Living in the Past”• Making up stories (confabulation)• Seeing or hearing things that are not really there

(hallucinations)• Damage to the thalamus and the mammillary bodies

Herpes Simplex Encephalitis (HSE)Clive Wearing

• Type I, II, Epstein-Barr virus, varicella-zoster• Sudden on-set • Very young and elderly or immune

compromised.

The Case of HM

• Bilateral Medial Temporal Lobectomy

– Removed his medial temporal lobes (MTL) bilaterally to alleviate serious epilepsy (1953)• Hippocampus• Amygdala• Rhinal Cortical Areas

– Epilepsy improved

– He was last patient to receive this treatment

• After surgery:– Intellect was above average• IQ actually improved from 104 to 118

– Normal perceptual and motor abilities– Well-adjusted individual– He was left with very poor memory abilities

–Mild retrograde amnesia (~ 2 years prior to surgery)–Profound anterograde amnesia

• HM is the most famous patient in the history of neuroscience research.

• He has served as an invaluable teacher of the neurobiology of memory and has been extensively tested for over 50 years.

• Demonstrated that the medial temporal lobe is critical for forming new memories.

• Video of HM-Died in 2010

Tests For Retrograde AmnesiaBoston Remote Memory Test

Famous Faces

Free recall portion: patients asked to recall the name of the person shown in the photograph (e.g., Telly Savalas). Participants were given ample time to respond.

If they were unable to recall the name, were given a series of cues. First, a semantic cue was given (e.g., "He was an actor, American, and had a popular series on TV").

If semantic cue fails a phonemic cue was given (i.e., the person's initials).

Four answer, forced choice test.(e.g., Yul Brynner, David Soul, Don Rickles, or Telly Savalas).

Past Public Events Test

Performance measured with a free recall test (e.g., "Who killed John Lennon?") and a four-alternative, forced-choice recognition test (names of individuals such as John Hinkley, Sara Jane Moore, David Roth, or Mark Chapman).

Both of these tests involve Semantic (fact based) as well as episodic memory.

Autobiographical Events(Personal Events)

Primarily of Episodic memory but some autobiographical semantic components.

Often difficult to assess the accuracy.

Theories of Amnesia

Encoding (Consolidation) Deficit Theory - AA due to a failure of encoding of new

material.- RA due to an undetected encoding failure

prior to diagnosis. (RA is actually due to AA) - this is possible for gradual onset disorder

(Alzheimer’s & Korsokoffs) but does not explain RA in sudden onset cases (HSE & Temporal Lobe Surgery).

Korsakoff’s Patient P.Z.(Butters & Cermak,1986)

P.Z. was an eminent university professor and scientist who had written his autobiography shortly before the onset of the clinical appearance of his disease. P.Z. had classic graded retrograde amnesia in which the events over five decades leading up to the clinical appearance of the disorder showed a systematic decline in recall.

Encoding (Consolidation) Deficit Theory Explanation

One explanation of P.Z.’s RA is that the disorder impaired consolidation of memories during a time prior to the diagnosis of Korsakoff’s syndrome, so that what appeared to be RA was really the long-term effects of AA.

Using his own biography, the investigators were able to test P.Z.’s memory for events in his life beginning in his early years, through his undergraduate and graduate training, and into his career and family life beyond.

Found recently acquired information, even was more vulnerable to interruption than more remote memories – suggesting a retrieval problem in RA.

Retrieval Deficit Theories of Amnesia

Retrieval impairment produces both AA and AR

Problems:- Predicts AA and RA should be equally as sever

in patients (and this is not true).

- Difficult to explain Focal AA and Focal RA

Separate Disorders of Encoding and Retrieval

Consolidation ModelConsolidation has two stages

- immediate – takes only a few seconds- longer – continues to strengthen trace for

two of three years - hippocampus - episodic turned to semantic

Variation in RA Periods

Some patients have very long-term RA (30 years in the case of the Korsakoff’s patient presented)

Some have very limited (HM only few years)

Consolidation model can not explain these differences.

Multiple Trace Theory

Hippocampus is involved in converting episodic to semantic (encoding). Once semantic, the memory is independent of the hippocampus.

Retrieval of episodic memories requires the hippocampus. Predicts that episodic memory for all time periods should be disrupted, but only recent semantic memories should be impaired.

Explaining the Temporal Gradient of RA

• Older memories have more retrieval routes.• Are more resiliently consolidated• Older semantic memories are independent of

the hippocampus.

Motor Skills Old motor skills tend to be retained and new motor skills can be learned (procedural memory) but they lack knowledge that they have learned the new skill (no declarative memory for the procedure).Newly learned skills do not generalize.

Implicit Memory

• Degraded Pictures test

• Many patients with organic amnesia are able to do as well as normal on implicit memory tasks while doing much poorer on explicit tasks.

Episodic and Semantic Memory

In general, episodic more severely impaired than semantic in Organic Amnesia patients.

Familiarity and Context

Babies Alternative

Organic Amnesic persons are able to tell that an object, place or person are familiar even when they do not recognize the context from which it is familiar.

Huppert and Piercy (1979) study

Declarative and Non-declarative

Organic amnesia patients are more impaired in declarative (consciously controlled) than non-declarative (automatic - implicit memory, procedural memory & familiarity).Hippocampus may be needed to “bind” a memory with its context. Non-declarative memory depends more on the cortex and the cerebellum.

Impaired STM

Associated with Frontal Lobe Lesions

Difficulty with contextual information- know facts, but not why they know them.

Schacter et al. (1984) Presented facts Remembered facts, but not where they learned them. Often confabulated where they learned the facts.

Impairment of Central Executive of Working Memory

Confabulation: Filling in memory gaps with a falsehoods that a person believes to be true.

Tendency to use Semantic information to fill in episodic or autobiographical memory. Failure of the executive function to verify the source or the context.

Normal Aging and Memory Loss

Decline in recall but not recognition .Decline in explicit but not implicit memory.Difficulty recalling contextual information.

- source of the information- time of the event.

Related to frontal lobe loss

Concussion AmnesiaMost common cause of amnesia

Anterograde amnesia (difficult to form and retain new memories). Amnesia is sometimes not noticeable until a few days or even a week after an injury or accident. e.g., sports player who retains detailed memories of what was happening during a game before an injury, but who has no recollection of what happened subsequent to the incident.

Generally, this is temporary.

Retrograde amnesia tends to be for a minute or two before the trauma (but could be days or weeks). Generally, this is permanent.

Normal STM (e.g., digit span)

Temporary inability to consolidate memories.

Memory Strategies for Amnesiacs

“Spaced” rather than “massed” learning.Leaning in various contexts.MnemonicsErrorless learningExternal Aids

- lists, simple written instructions- higher tech gadgets (pagers, alarms & cameras).

Psychogenic Amnesia (functional or dissociative)

- severe stress or psychological trauma

Global amnesia - (fugue state) - sudden loss of personal identity

- severe stress or depression - extended periods of wandering and confusion.

Very rare, and usually resolves over time (although memory of the fugue episode itself may remain lost).

Situation-specific amnesia - type of psychogenic amnesia that occurs as a result of a severely stressful event.- normal autobiographical memory processing blocked by imbalance of stress hormones (e.g., cortisol) particularly in the regions of the limbic system.- often difficult to distinguish a true repressed memory from a false one without corroborating evidence.