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. Using an autoradiographic technique, we obtained evidence that there are afferents in the skin of the head that project directly to the pedal ganglion 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 cerebral-pleural connective did not differentially affect turns evoked by stimuli applied ipsilaterally or contralaterally to the lesion. However, a combined unilateral lesion of a cerebral-pedal and cerebral-pleural connective resulted in elimination or significant reduction of ipsilateral turns. The data suggest that head turns elicited by food, are mediated by the combined information travelling in both the pedal and pleural connectives.