The Biopsychology of
Learning and Memory

Chapter 13

Early Proposal

u Pavlov – learning (such as classical conditioning) strengthens the connections between the involved brain areas

u If this is the case, disrupting these connections should impair the learned response

Early Research

u Karl Lashley – attempted to locate memory “engrams” in rats’ cortex by studying the effects of cortical cuts or lesions

u Law of equipotentiality – all areas of cortex seemed to be equally important to the performance of the learned response – no single critical “memory area”

u Law of mass action – degree of impairment was correlated with amount of cortex removed, not the region of the cortex removed

u Lashley was probably misinterpreting his results

Lashley’s Cuts in Rat Cortex

Successful Location of An Engram?

u Richard Thompson found a nucleus in the cerebellum (LIP – lateral interpositus) essential for the conditioned eyeblink response of rabbits

– Neurons active during this learning

– Inactivating these neurons disrupts conditioning

– These neurons also appear to be active in humans during eyeblink conditioning

Hebb’s theory of memory “consolidation”

u Hebb distinguished between STM & LTM

u Proposed STM mediated by temporary activity in “reverberating circuits”

u LTM depends on structural changes

u Increased connectivity resulting from repeated activation of the same synapses caused the “consolidation” of LTMs

Retrograde Amnesia
by ECS or Other Traumas

u Recent memories most susceptible to disruption

u Rats given ECS 10 secs to 10 mins after learning showed decreased memory for task. ECS 1-3 hrs after learning had no effect.

u Humans receiving ECT show decreased recall of TV shows from last 1-3 years, no impairment of memory of shows from 4-17 years ago.

Retrograde vs. Anterograde Loss

Prefrontal Cortex & Working Memory

u Animals or people with prefrontal damage are impaired on delayed response tasks

u Monitoring brain activity reveals that the prefrontal area is active during the delay

u Different cells in the prefrontal region seem to represent temporary memories of different locations or stimuli

Delayed Response Task

Piecing Together the Human Memory System From Case Reports

Different Aspects of Memory

u Declarative memory – memories we can state in words

u Procedural memories – motor skill memories

u Explicit memory – conscious intentional recollection

u Implicit memories – memories evidenced by improved/altered performance without conscious recollection

The Sad Case of H. M.

u Focal epilepsy uncontrolled by medication

u Had bilateral medial temporal lobectomy

u Epilepsy improved but memory impaired

u Severe anterograde amnesia for declarative memories. STM normal but once HM is distracted, those memories are lost.

u Some retrograde amnesia for things within the 2-3 years before surgery, but older memories and IQ intact

Quote from H.M. (Milner, 1970)

u Right now, I'm wondering: Have I done or said anything amiss? You see, at this moment everything looks clear to me, but what happened just before? That's what worries me. It's like waking from a dream; I just don't remember.

H.M. continued

u H.M. has shown evidence of the formation of new procedural & implicit memories

u Finger maze, mirror tracing, rotary pursuit, classical conditioning

Mirror-Drawing Task

Clive W.

u Suffered damage to hippocampus and frontal cortex during a bout of encephalitis (this is the case that starts the chapter)

u Extreme anterograde amnesia similar to H.M.’s although his old LTM s are fine

Amnesia Due to Diencephalon (Thalamus/Hypothalamus) Damage

u Korsakoff’s Syndrome - serious anterograde & retrograde amnesia but once again implicit memories are better preserved. Tendency to confabulate.

u Due to thiamine deficiency which impairs the supply of energy (glucose) to the brain

u Widespread loss of neurons, most concentrated damage in mammillary bodies & DM thalamus

Alzheimer’s Disease

u Several pathological changes in brain

– Production of abnormal amyloid protein which damages neurons, causing distinctive tangles & plaques of neural debris

– Neuron loss heaviest in association cortex areas, medial temporal lobes, and basal forebrain (nucleus basalis of Meynert)

– dramatic decline in cholinergic (Ach) activity in the forebrain

u Runs in families; genes on at least 4 different chromosomes have been linked to AD (21, 14, 1, 19)

u Progressive decline in almost all aspects of memory & cognitive abilities

Memory Role of Other Areas

u Frontal lobe - memory for temporal order

u Amygdala - emotional significance

u Cerebellum & Basal Ganglia - implicit, procedural memories

u Long-term memories seem to be stored in the secondary & association cortex areas involved in the original stimulus perception