Effects of contralateral cutaneous afferent activity on acquisition of a nictitating membrane response.

Stcmmary.-The effects of 2 different levels of contralateral cutaneous afferent activity on acquisition of rhe nictitating membrane response in 2 groups of rabbits was examined. Differences in the level of contralateral afferent activity from the primary response area were found to have no statistically significant effect on the acquisition rates of an ipsilaterally developed nictitating membrane response. A decrease in cutaneous afferent activity from the primary response area (roughly the cornea and paraorbital region) has been found to attenuate greatly learning of the classically conditioned nictitating membrane response in rabbits (4). Although it is reasonably certain that afferent activity outside this area on the ipsilateral half of the face does not influence learning, its importance from the contralateral homologous primary response area has not been determined. The reason for questioning whether contralateral cutaneous afferent activity from the primary response area might be important comes from Poggio and Mountcastle's (6) work in the somatosensory system. They observed that certain cells within the nuclei comprising a portion of the paleospinothalamic system responded equivalently to sensation from some homologous regions of the body. It is possible that those neural structures essential for the expression of cutaneous a€ferent activicy on learning might also be affected by sensation from the contralateral primary response area. In the present study this question is examined by comparing acquisition rates in the trained right eye, in two groups, of the nictitating membrane response under the same ipsilateral levels of cutaneous afferent activity. Cutaneous sensation from the contralateral eye was different for the two groups-being higher in one group than in the other. This procedure was not expected to decide whether central afferent neural interaction between homologous somatic areas exists in this response system but rather to determine whether such interacrions, if present, have functional significance for learning of the nictitating-membrane response. Method.-Ss were 18 New Zealand albino rabbits (Osyctolagus cuniculus) of both sexes, weighing 4 or 5 lb., obtained from a local supplier. All animals had ad lib. access to food and water and were maintained in lighted, well ventilated, temperature controlled quarters. The procedures and apparatus to be discussed have been previously described in greater detail by Gormezano (3). Preliminary preparations consisted of tying a nylon loop of thread into the nictitating membrane of the tight eye, 48 hr. prior to the first scheduled conditioning session. In each animal two 9-mm., stainless steel, Clay Adarns wound clips were implanted 3/8 to M in. apart at the tip of the right ear. On the following day, each S was placed in a Plexiglas restraining box having an adjustable back plate, head yoke and foam rubber padded ear clamp. Thus prepared, all Ss were placed in a darkened, sound attenuating chamber for 15 min. to habituate them to the experimental enclosure and apparatus. All Ss received daily corneal applications of an oxgtetracycline ophthalmic ointment after training to offset the possibility of infection. In the event that this proved insufficient, l/z cc. I.M. injections of oxytetracycline were also given. Movements of the nictitating membrane were monitored by a photoelectric transducer mounted on S's head by means of a muzzle-like assembly. The transducer was