Orienting response hypernormality in frontal cats.

Results obtained in collaboration with B. Dreher are summarized. Ocular fixation was the indicator of the orienting response, and pupillary dilatation and ECoG arousal to olfactory stimuli were the indicators of the arousal response. To make precise recording possible, animals with pretrigeminal brain stem transection were used. After ablation of the anterior sigmoid gyrus or proreal gyrus the fixation response was enhanced and its resistance to habituation was strongly increased. On the other hand, the pupillary dilatation and ECoG arousal to olfactory stimuli and the background pupillary diameter and ECoG activity were unaffected. The hypernormality of the orienting response can be partially responsible for the disinhibition of the locomotor responses in go-no go differentiation and for the impairment of locomotor delayed responses in frontal carnivores.