Transcript Topic 23

Biology 463 – Neurobiology
Topic 23
Wiring of the Brain,
Memory Systems,
And
Molecular Mechanisms
Lange
The Search for the Engram
Engram - 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.
•
Lashley
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
Three different regions were lesioned in the rats:
Yellow – frontal lobe
Blue – temporal lobe
Orange – 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.