DIFFERENTIAL ROLES OF CEREBELLAR CORTEX AND DEEP CEREBELLAR NUCLEI INTHE LEARNING OF THE EQUILIBRIUM BEHAVIOR - STUDIES IN INTACT AND CEREBELLECTOMIZED LURCHER MUTANT MICE

Three- to 6-month-old lurcher mutant mice (+/lc), which exhibit a mass ive loss of neurons in the cerebellar cortex and in the inferior oliva ry nucleus but whose deep cerebellar nuclei are essentially intact, we re trained daily, for 9 days, to maintain their equilibrium upon a rot a rod rotating at 20 or 30 revolutions per minute (rpm). Their scores were measured and their behavior upon the rotating rod quantified in c omparison to those of matched control (+/+) mice. Lurcher mice were ab le to learn to maintain their equilibrium efficiently when rotated at 20 rpm but were not when rotated at 30 rpm. After cerebellectomy, the equilibrium capabilities of the animals were much altered, especially in +/lc. These results show that the deep cerebellar nuclei are suffic ient for motor learning, provided the task is not too difficult (20 rp m), but that the cerebellar cortex is required when the task is more d ifficult (30 rpm). Therefore, it can be concluded that the adaptive mo tor capabilities of lurcher mice are less developped than those of con trol animals.