The effect of hyperstriatal lesions on head orientation to a sound stimulus in chickens

Abstract

In a previous study responses to click stimulation have been recorded from the three upper hyperstriatal layers of the chicken's telencephalon. The present investigation was undertaken to determine the functional role of these hyperstriatal regions in the chicken's reflex head orientation to a sound stimulus, and, to examine hyperstriatal function in the habituation of this response. Half of the chickens were presented with 0.2 sec of white noise; the other half with 2 sec of the same stimulus. Head orientation responses were observed, rated, and recorded following presentation of the sound stimulus for ten consecutive trials during each of five test sessions. Following preoperative testing, bilateral hyperstriatal lesions were produced surgically and seven days later the preoperative testing procedure was repeated. Unoperated and sham operated controls were treated similarly. Significant intersession habituation of the head orienting response occurred only preoperatively for both groups. Significant intrasession habituation was absent preoperatively and postoperatively for the two groups. Hyperstriatal lesions significantly affected the final preoperative level of habituation of the response for the 0.2-sec group. Postoperatively there was a significant increase in the average number of incorrect responses for all bilaterally operated subjects. These data indicate that the hyperstriata, especially the accessory hyperstriatum, in chicken play a functional role in habituation of the head orienting response to sound stimulation and in localization of sound in space.