Effects of posterior parietal lesions (area 7) on VOR in monkeys

Unilateral ablations of area 7 were performed in three adult monkeys. Vestibulo-ocular reflex (VOR) was tested in the dark by sinusoidal rotations at different frequencies. Following lesion of area 7, spontaneous nystagmus was observed in the dark, with the fast phase directed toward the lesioned side. The same lesion induced a strong VOR asymmetry due to a gain decrease when the animal was rotated toward the side contralateral to the lesion and an increase when rotated toward the opposite side. These VOR deficits were transient: spontaneous nystagmus was no longer present after the first post-operative week whereas the VOR asymmetry lasted for 2 to 4 weeks after the lesion. It is concluded that area 7 might be involved in an ipsilateral control of the slow component of VOR. These results support the idea that posterior parietal cortex plays a role in body reference stabilization.