Visual neglect in pretrigeminal cats with lateral suprasylvian lesions

Eleven cats with brain stem transected at the pretrigeminal level were used. The cortex of the middle suprasylvian sulcus was removed on the left side. The vertical following reflex was evoked by a slit of light (1 degree x 4 degrees) or a black bar (1 degree x 1 degree x 4 degrees) moving along the vertical meridian or parallel to it out to 40 degrees in the left or right hemifield. In all cats the following reflexes to the contralesional hemifield were low or absent. A corresponding suprasylvian lesion was made subsequently on the right side. In 6 cats the reflexes to both hemifields were absent or low. In contrast, surprisingly in 5 cats the reflexes were large, much higher than those evoked previously from the contralateral hemifield after the first lesion. This might be due to a process of disinhibition occurring in the superior colliculi.