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Lecture 4

Lecture Four Part 2 Associative types of learning Part 2. Discussed Kandel and his experiments with Aplysia. Went into detail about the Aplysia model for reaction to conditioning. Talked about food conditioning and aversive conditioning (based on Pavlov’s

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Martin Ralph

Continued in from Lecture Four Part 1ERKandelRecognized that organisms that had simple nervous systems few neurons have to accomplish the same sorts of tasks as more complex organisms but with less We humans may be a little more exact and precise in our responses but they are ultimately the same as a sea slugs At the basic level we do the same things we need things and avoid things for survival Our nervous system is there to get us what we need and avoid what will harm us If we look at aplysia we see an organism with only a few hundred neurons to control everything He recognized that there were different behaviours that can be exploited in aplysia different types of responses that could be elicited that could be subjected to associative learning conditions To put very simply aplysia dont like to be touched and they respond to when they are touched This is usually a defensive type of response and there are numerous defensive responses all of which tend to be withdrawal type responses These are subserved by different parts of the nervous system Kandel wondered whether or not the very basic changes in neural transition could be modeled in this relatively simple circuit The simple association that they exploited was the gill withdrawal reflex The gill is an important organ that extracts oxygen from the water It hides in the mantle of the organism when it is attacked or disturbed and emerges when the danger has passed What they found was that the sensitivity of the gill is very high which makes logical sense and that the withdrawal response is caused by an unusual touch that is not elicited by the organism itself aplysia will not withdraw their gills if they are moving along a rocky surface Now if you keep touching and touching and touching this gill it will eventually not withdraw The associative experiment was to pair the slight touch with a major stimulus to the tail A touch to the tail electrical stimulation causes withdrawal of the tail and if it is strong enough it will cause a general contraction But the main experiment was to to link this light touch to the siphon with the rather large unconditioned stimulus in the tail What they found was that as long as the touch to the siphon preceded the large stimulus to the tail the touch to the siphon became associated with that major deleterious tail stimulation You could then elicit a large response to the gill with a light touch This diagram was created very early on to try and explain what was going on in the experiment Here we have a shock to the tail that produces sensory input and a contraction of the gill siphon and tail The touch
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