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Evolution+of+Learning+_+Memory

Evolution+of+Learning+_+Memory - Evolution of Learning...

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Evolution of Learning Cognition begins with action. An action is the movement of a body part in response to some target perceived by an animal. So falling off a cliff and being blown in the wind do not count as actions. Rather, action implies perception because the animal must be able to perceive the target that the action is in response to. If you cannot move about and have an effect on your place in the world then there is no value to you in perceiving and thinking about the world. For example, since plants have no muscles, there is no point in having a nervous system so that they could perceive the world and think about the things they couldn’t do. Learning and Memory Learning begins with increasing the effectiveness of action. Consider the Aplysia, a little sea snail that Eric Kandel studied to work out the neural mechanism of the habituation and sensitization of a simple reflex. Touching its siphon lightly produces a brisk defensive withdrawal of both the siphon and the gill. How forceful a touch is required? This varies with the experience of the individual. Repeated light touch produces habituation . That is, after each touch the withdrawal of the siphon is slower until it doesn’t withdraw at all. A strong shock to either head or tail produces sensitization . That is, after the strong shock, weak touch that previously did not cause the withdrawal of the siphon, now does. Why should the fine-tuning of a reflex through habituation or sensitization be of benefit to the animal? The withdrawal of the siphon is only of benefit if the animal was actually threatened. If the animal is in a benign environment, disturbed only by an occasional puff of air, then habituation reduces the likelihood of a pointless response. On the other hand, once banged on the siphon, twice shy. If the Aplysia has been not merely touched, but poked hard enough to elicit a large response from its nervous system then the siphon has been withdrawn in response to danger. All the better if it withdraws sooner and faster the next time that something makes contact with the siphon. Both habituation and sensitization are useful as long as events in the world are not completely random, so that there is a routine to adjust to. Habituation adjusts the probability of the withdrawal reflex to the routine of a benign world. Sensitization adjusts the probability of the withdrawal reflex to the routine of a more dangerous world. Kandel and his colleagues showed that habituation and sensitization occurred at the synapse between the sensory neuron that detected a tactual input from the environment and a motor neuron that caused the siphon to contract. A neuron communicates with its neighbors by releasing a neurotransmitter into the gap, called a synapse, between them.
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