EFFECTS OF MIDLINE AND LATERAL CEREBELLAR LESIONS ON MOTOR COORDINATION AND SPATIAL ORIENTATION

Rats were lesioned in the midline cerebellum, comprising the vermis an d fastigial nucleus, or the lateral cerebellum, comprising the cerebel lar hemispheres and dentate nucleus, and evaluated in a series of moto r and non-motor learning tests, Rats with midline lesions had difficul ty in maintaining their equilibrium on a bridge and were slower before turning upward and traversed less squares on an inclined grid. They w ere not impaired for muscle strength when suspended from a horizontal wire. Rats with lateral lesions had milder deficits on the bridge and were not affected in the other two tests. In the Morris water maze tes t, rats with lateral lesions were deficient in spatial orientation, wh ereas rats with midline lesions were deficient in visuomotor coordinat ion. Lateral lesions had no effects on visual discrimination learning. These results illustrate the differential influence of midline as opp osed to lateral cerebellar regions on both motor and non-motor behavio rs. Fastigial nucleus lesions decreased the time spent in equilibrium and latencies before falling on the bridge and the distance travelled along the inclined grid but had no effect on muscle strength when susp ended from the horizontal string. Quadrant entries and escape latencie s were higher in rats with fastigial lesions during the hidden platfor m condition of the Morris water maze but not during the visible platfo rm condition. It is concluded that fastigial-lesioned rats are impaire d in equilibrium and spatial orientation but with repeated trials lear n to improve their performances.