Topic 23

Wiring of the Brain,

Memory Systems,

And

Molecular Mechanisms

Lange

Biology 463 – Neurobiology

The Search for the EngramEngram - a means by which memory traces are stored. As memory is a result of experience, the idea of the engram is a sort of “mapping” of experiences in life.

Engrams are thought to encompass both biophysical and biochemical changes in the brain (and potentially other neural tissues) in response to external stimuli.

In this human study, by Chris Stephenson in 2007, he showed memory associations with a variety of online services. He was attempting to combine aspects of engram study with ecology.

http://chrisstephenson.typepad.com/chrisstephenson/2007/12/the-ecology-of.html

Karl Spencer Lashley studied rat learning via mazes.

• Tests involved the ability to learn to navigate the maze without errors

•Lesions were created in areas of the brain suspected to be associated with memories and of ability to learn

Lashley

Three different regions were lesioned in the rats:

Yellow – frontal lobeBlue – temporal lobeOrange – occipital lobe

The greater the % of cortex destroyed, the greater the number of errors. This work showed that the cortex is highly significant for both memory and learning.

Hebb’s Cell Assembly and Memory Storage suggests:

•Experience of an external stimulus (a) will activate an assembly of neurons

•Reverberating circuits reinforce the assembly

•Even a partial stimulus (b) will reactivate the assembly

•The “circle” in (c) suggests the engram or memory

The Temporal Lobes and Declarative Memory (2 Maze Types)

• Radial arm maze (a)– (b) Normal rats go down each arm for food only once

– hippocampal lesioned rats will revisit arms again and again

– (c) Normal and lesioned rats do eventually can learn which arms are baited and avoid the rest

• Morris Water Maze- memory and anxiety tested

Associative Learning– Classical Conditioning: Pair an unconditional stimulus (UC) with a

conditional stimulus (CS) to get a conditioned response (CR)

Ivan Pavlov

END.