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.