NEURONAL PATHWAYS MEDIATING HEAD TURNING BEHAVIOR IN APLYSIA

Seaweed applied to the head of Aplysia elicits a head turning response in the direction of the stimulus. The major motor neurons involved in head turning appear to be located largely in the pedal ganglion. Usin g an autoradiographic technique, we obtained evidence that there are a fferents in the skin of the head that project directly to the pedal ga nglion-by way of the cerebral-pleural connectives. Bilateral lesioning of the cerebral-pleural connectives, however, did not interfere with head turning, and unilateral lesions of either a cerebral-pedal or cer ebral-pleural connective did not differentially affect turns evoked by stimuli applied ipsilaterally or contralaterally to the lesion. Howev er, a combined unilateral lesion of a cerebral-pedal and cerebral-pleu ral connective resulted in elimination or significant reduction of ips ilateral turns. The data suggest that head turns elicited by food, are mediated by the combined information travelling in both the pedal and pleural connectives.