Development of behavior and learning inAplysia

Abstract

A set of fundamental issues in neuroethology concerns the neural mechanisms underlying behavior and behavioral plasticity. We have recently analyzed these issues by combining a simple systems approach in the marine mollusc Aplysia with a developmental analysis aimed at examining the emergence and maturation of different forms of behavior and learning. We have focussed on two kinds of questions: 1) How are specific neural circuits developmentally assembled to mediate different types of behaviors? and 2) how is plasticity integrated with these circuits to give rise to different forms of learning? From our analysis of the development of learning and memory in Aplysia, several themes have emerged: 1) Different forms of learning emerge according to different developmental timetables. 2) Cellular analogs of learning have the same developmental timetables as their respective forms of behavioral learning. 3) An analysis of non-decremented responses prior to the emergence of sensitization reveals a novel inhibitory process on both behavioral and cellular levels. 4) Sensitization emerges simultaneously in diverse response systems, suggesting an underlying general process. 5) A widespread proliferation of central neurons occurs in the same developmental stage as the emergence of sensitization, raising the possibility that some aspect of the trigger for neuronal proliferation may also contribute to the expression of sensitization.

Habituation may contribute to within-session decreases in responding under high-rate schedules of reinforcement

“…These results may suggest that manipulations that change habituation need to be presented for a long time to alter the x-axis intercept. As an alternative, some authors have argued that dishabituation is actually sensitization rather than a release from habituation (e.g., Groves & Thompson, 1970; but see Marcus, Nolen, Rankin, & Carew, 1988). Because sensitization is thought of as an independent process with an intrinsic decay time course, it might not affect the habituation process.…”

Massed and spaced training build up different components of long-term habituation in the crabChasmagnathus

“…Thus, as cited in the introduction, a distinction between two memory components has been proposed concerning odor avoidance conditioning in Drosophila (Tully et aI., 1994)-namely, an anesthesia-resistant memory produced by either massed or spaced training, insensitive to cycloheximide and disruptable by the radish singlegene mutation (Folkers, Drain, & Quinn, 1993), and a long-term memory yielded only by spaced training, disruptable by cycloheximide but not by the radish. Similarly, a different stimulus requirement was one of the grounds for distinguishing between two modalities of an associative learning in Drosophila-namely, dishabituation induced by a weak stimulus and sensitization by a strong stimulus-likely reflecting different underlying mechanisms (Marcus, Nolen, Rankin, & Carew, 1988).…”

General-process theories of motivation revisited: The role of habituation.

“…Dishabituation may not be the release from habituation that its name implies. Rather, it may be produced by Sensitization (see, e.g., Groves & Thompson, 1970; but see Marcus, Nolen, Rankin, & Carew, 1988). Regardless of whether dishabituation is an example of sensitization or not, it is a fundamental property of habituated behavior (see, e.g., R. F. Thompson & Spencer, 1966).…”