Cerebral influence on postural effects of cerebellar vermal zonal lesions or eighth nerve section in monkeys.

In monkeys, cerebellar vermal cortical or fastigial nuclear lesion resulted in no significant postural asymmetry. Combined decerebration (but not bulbar pyramid section) and unilateral vermal cortical or fastigial nuclear lesion gave marked ipsilateral hyperextension and contralateral hyperflexion of limbs. Unilateral eighth nerve section resulted in only ipsilateral head tilt but combined unilateral eighth nerve section and decerebration or bilateral or contralateral cerebral cortical areas 4 and 6 lesion gave also ipsilateral flexion and contralateral extension of limbs. Cervical deafferentation or postbrachial spinal cord transection did not alter these results. This study indicates a powerful cerebral influence on postural effects of cerebellar vermal zonal lesion or eighth nerve section in monkeys. Possible mechanisms mediating these effects in monkeys as compared to cats were discussed.