Isolated-brain parallels to simple types of learning and memory in Tritonia

Physiological studies of learning and memory often require reduced nervous system preparations that can be trained by stimulation of neural pathways in a manner that mimics behavioral training. In the isolated brain preparation of the seaslug Tritonia, fictive swimming can be activated with a few electrical pulses applied to the cut end of a nerve, and learning experiments can be simulated with combinations of nerve stimuli. Repeated application of a nerve stimulus produced changes in fictive swimming that resembled habituation and iterative enhancement of multiple components of the swimming behavior. Many repetitions of the nerve stimulus led to fictive swimming failure. Stimulation of another nerve then restored the ability of the original nerve to activate fictive swimming, thus reproducing dishabituation results. Sensitization of threshold and latency were also simulated. Parallels between the behavior and the isolated brain suggest that the neuronal modifications underlying simple types of learning can be induced by nerve stimulation. The activity pattern of interneuron C2 in these experiments suggests that increased C2 synaptic efficacy may underlie sensitization of swimming latency. (C) 1997 Elsevier Science Inc.