Synaptic basis of memory - 13

Question 1

What was the earliest search for the engram?

Answer 1

Lashley - interested in the cortex and what part was responsible for maze learning. Surgically made lesions to the cortex and then observed how well a rat was able to work through the maze. Found discrete lesions of cortical areas did not interfere with maze learning, but large areas of damage did. From this created two principles:

1. Principle of Equipotentiality: all cortical regions can mediate learning equally.
2. Principle of Mass Action: ability to learn is proportional to the amount of cortex available.

Question 2

What are modern ideas are learning areas in the brain?

Answer 2

There are areas of the brain that are engrams for certain types of memory - subcortical areas involved in learning and memory e.g. hippocampus and the amygdala.

Question 3

What are dedicated memory storage areas of the brain?

Answer 3

1. Hippocampus - declarative and spatial memories e.g. H.M.
2. Cerebellum - procedural memories (simple Pavlovian associations)
3. Amygdala - emotional memories - Pavlovian associations
4. Frontal cortex - short-term/working memory.

Question 4

What is Pavlov’s synaptic basis of learning and memory?

Answer 4

Speculated that whatever part of the brain is responsible for processing auditory stimulus and taste stimulus that there is some growth/connection established that links the auditory centre with the food centre of the brain - creating new cortical connections.

Question 5

What is the cellular basis of memory?

Answer 5

Neurogenesis = when code memory get new neurons. Evidence for this way sparse up until mid 1990s. Now have some evidence neurogenesis does occur in the mammalian brain (olfactory bulb, hippocampal formation, possibly the neocortex)

Question 6

What is the structural basis of memory?

Answer 6

Cajal proposed that structural/morphological changes store memories e.g. the formation of new synapses, growth of dendritic processes (branches and spines)

Question 7

What is the synaptic basis of memory?

Answer 7

New synapses could be generated to store specific new memories. Spines grow to make new connections between neurons.
Existing synapses could be modified to store the memories. Efficacy changes (increases).
A pool of new synapses could be continuously generated in the brain, learning and memory incorporates them into a functional storage network. When learn something, new synapses become stabilised (relatively permanent connections).

Question 8

What was Hebb’s idea?

Answer 8

New synapses are anatomically and physiologically connected, but not part of a memory network.
Upon appropriate activation - synapses are “strengthened” and incorporated into a memory network.

Question 9

What is long-term potentiation (LTP)?

Answer 9

Long lasting changes in hippocampal synaptic efficacy following high frequency (tetanic) stimulation.