Journal of Neuroscience, Vol 9, 3115-3122, Copyright © 1989 by Society for Neuroscience
Operant conditioning of head-waving in Aplysia. III. Cellular analysis of possible reinforcement pathways
DG Cook and TJ Carew
Department of Psychology, Yale University, New Haven, Connecticut 06520.
Operant conditioning of the head-waving response in Aplysia, as well as
conditioning of the electrical activity of identified neck muscles, can be
induced readily when bright light is used as aversive reinforcement (Cook
and Carew, 1986, 1989b). A cellular analysis of this type of operant
conditioning requires an understanding of the neural circuitry that
underlies the reinforcement pathways involved in the conditioning. In the
present paper we describe a cellular analysis of possible reinforcement
pathways that mediate the aversive effects of bright light in the CNS of
Aplysia. Using a semi-intact "split-body" preparation, we explored the
effects of bright light on the operant response pathway by recording
intracellularly from identified pedal neck and body wall motor neurons,
which contribute to the operant response. In these experiments we
identified 2 light-sensitive pathways. One pathway, from the eyes and
rhinophores, mediated functional inhibition of light-induced excitation of
pedal motor neurons. The other pathway, from the oral veil (cerebral
ganglion nerves C1-C3) mediated significant excitation of the same motor
cells. Randomly occurring blank trials ruled out the possibility that the
light-induced effects were due to sampling bias. Finally, surgical
isolation of the CNS from the periphery showed that none of the effects of
light were due to direct illumination of central neurons. This
identification of candidate reinforcement pathways will facilitate a
cellular analysis of operant conditioning of head-waving in Aplysia.
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