BIOLOGICAL BASIS OF MEMORY

Biological Basis of Memory

Believed that memory was localized – specific memory stored in a specific area.

Removed parts of rat’s cerebral cortex but found no one area contained the memory of the maze

Found that maze-learning in rats was distributed throughout the brain

Karl Lashley searched for a localized memory trace or engram

Memory and the Brain

• Play “The Locus of Learning and Memory” (6:28) Module #16 from The Brain: Teaching Modules (2nd edition).

• Watch first 3 minutes on Lashley’s Experiment and if time view Penfield’s experiment & why it was flawed.

Biological Basis of Memory• Thought that cerebellum

was changed after classically conditioning a rabbit to blink to a tone. He was right!

• Removing this area caused the rabbit to no longer blink to a tone but only reflexively. Shows localized memory.

• This did not work for complex behaviors like running a maze, which seem to be distributed

Richard Thompson

Reflexive Behaviors are localized in the cerebellum

Biological Basis of Memory

• fMRI shows that when people memorized the label “dog” with the sound of a bark the auditory cortex activated when they retrieved it.

• Those memorized the label “dog” to a picture activated their visual cortex when they retrieved it.

• Retrieving a memory reactivates the sensory area of the cortex that was involved in the initial perception of the event. (See images on pg. 268)

New Memories in a Snail• Aplysia—a sea

snail was used to study how memories can change neurons

Eric Kandel

Kandel’s Sea Snail Experiment• Eric Kandel – studied neural changes that took place in

Aplysia, a sea snail. Click HERE to view it (4 min)• Squirted it with water followed by an electric shock that

classically conditioned it to withdrawal its gills next time it was squirted.

• This changed the three neuron circuit in the snail.• Function of the neuron changed with increase in the

amount of the neurotransmitter produced by the neuron.• Structure of the neuron changed with the number of

interconnecting dendrites and axon terminals increasing allowing for more communication points (synapses).

Long-Term Potentiation

• Two possible changes should occur in the neurons in forming memories.1. Functioning of neurons in the brain could change

2. Structure of the neurons could change.

• These increase the neuron’s firing potential

• Kandel’s experiment shows this.

• Believed to be the neural basis of learning and memory

Severe Memory Loss• Amnesia—severe memory loss

3 Major Types:

1. Retrograde Amnesia

2. Anterograde Amnesia

3. Infantile Amnesia

Retrograde amnesia• Retrograde amnesia—inability to remember PAST

episodic information; common after head injury;

Reason for this is it may disrupt:– Memory Consolidation – gradual, physical process of

converting a long-term memory to a stable and enduring memory code.

– If disturbed before the process is complete, memory could be lost.

– Sleep seems to be when most memory consolidation occurs

Anterograde amnesia• Anterograde amnesia—inability to form NEW

memories; related to hippocampus damage– Shows that hippocampus must be used in the

encoding of new memories and transferring them from STM to LTM.

– Implicit memories like procedural memories do still occur showing that these may not involve the hippocampus but knowing they are there (explicit memory) does not work showing the hippocampus is involved in these.

Infantile Amnesia• Infantile Amnesia – Inability to recall events from

the first few years of life. • Possible Reasons for this:

1. Too many differences between the world of an infant and ours for us to be able to make connections or retrieval cues to retrieve them (encoding specificity principle).

2. Hippocampus is still developing so they cannot form new LTM but they can make procedural memories.

3. One reason adults typically recall little of their first three years of life is that during infancy they were unable to verbally label most of their experiences (semantically encode the info).

Brain Structures Involved in Memory

Emotions & the Amygdala• Amygdala may help in formation of emotional

memories.

• Watch Enhancing Memory (7:50) to see how research is showing this. Click below.

Evidence for Separate Implicit/Explicit Systems

• Neurophysiological evidence• Patient H.M. (Henry Gustav Molaison)

– life-threatening seizures originating in temporal lobe

– surgically removed portions of temporal lobe

Temporal Lobe

• Includes:– hippocampus– Amygdala

• Verbal information is stored in the left hippocampus and

• Visual designs are stored in the right hippocampus

Patient H.M.

• Click HERE for a video on H.M. (10 Min)• Surgery was effective in reducing seizures• BUT, had other side effects as well• Can remember explicit memories acquired before the

surgery– e.g., old addresses, normal vocabulary

• Cannot form NEW explicit memories– e.g., remembering the name of someone he met 30 minutes prior– cannot name new world leaders or performers– can recognize a picture of himself from before his surgery but

not from after and doesn’t recognize himself in a mirror

Patient H.M.• H.M. has severe explicit / declarative memory disorder

• H.M. is almost normal on procedural or implicit memory tasks including priming, classical conditioning, and learning motor skills

• When given the same logical puzzle to solve for several days in a row, H. M. was able to solve the puzzle more quickly each day.

• This shows that explicit memory depends upon the temporal lobes and implicit does not

Patient H.M. Summary

• Temporal lobe damage led to deficits in explicit, but not implicit memory– H.M. had both episodic and semantic memory deficits

• Damage to the hippocampus alone produces episodic, but not semantic memory deficits

• Why did H.M. show both types of explicit memory deficits?– He had damage not only to hippocampus, but to other

structures as well

Memory and the Hippocampus• Damage to the hippocampus would

result in the inability to form new explicit memories, but the ability to remember the skills of implicit memories

•To view someone with this damage checkout the video by clicking on it (7:38)

Memory and the Hippocampus

Hippocampus and Memory

• Play “Living with Amnesia: The Hippocampus and Memory” (10:35) Module #18 from The Brain: Teaching Modules (2nd edition).

• Watch if Time Allows.

Aging and Memory

• Studies have found that the ability to recall new information, unaided by clues, declines with age,

• But the ability to recognize new information, as in a multiple-choice question, does not.

• Elderly may need more time to retrieve memories but still can do as well as a young person.

Culture & Memory

• Levy and Langer study of cultural views of aging show that society’s expectation that older people will have poorer memories can be a self-fulfilling prophecy.

• In cultures where that is not believed (Asia) the elderly show memories just as good as the young.

Think your memory is something special?