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Krasnow Institute > Monday Seminars > Abstracts Behavioral and Pharmacological Aspects of Learning in Crabsc Daniel Tomsic Invertebrates proved to be valuable models for studying the physiological basis of memory. These animals possess a relatively simple nervous system but with the capability to acquire long-term memories. More than a decade ago we began a systematic study of habituation of the escape response to a visual danger stimulus in the crab Chasmagnathus granulatus. In nature, this crab is chased by gulls. In the laboratory, upon sudden presentation of a rectangular screen passing overhead, the crab responds with a running reaction in an attempt to escape. The response declines over trials and, after a single training session of 15 trials (1h), the decrement persists for several days. The response decrement was shown to be stimulus specific, frequency specific and both age and time-of-day dependent. The adaptive value of this remarkable memory capacity of Chasmagnathus was studied by comparing it with that of Pachygrapsus, that is, by comparing the ability for long-term habituation in two species close in phylogeny but disparate in ecology. Interestingly this long-term habituation processes is context specific, revealing to be formed by two different memory elements: a nonassociative component and an associative component. Both memory components can be dissected according to the training procedure applied. On the other hand the associative component is disrupted by protein syntheses inhibitor while the nonassociative component is not. Thus, our results indicate that depending on the adaptive value for the species, habituation can be a quite complex memory phenomenon.
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