Immediate early gene expression in the cerebellar vermis of cats and squirrel 
monkeys was stimulated by prolonged whole body rotations. Continuous, 
earth-horizontal axis rotations that excited only otoliths or high velocity 
vertical axis rotations that excited only semicircular canals resulted in c-fos 
immunoreactive nuclei concentrated in the granular layer of lobules X and 
ventral IX (the nodulus and ventral uvula), which represent the medial parts of 
the vestibulo-cerebellum. Large clusters of labeled nuclei consisting mainly of 
granule cells and calretinin-positive unipolar brush cells were present in the 
granular layer, whereas Purkinje cell nuclei were unlabeled, and labeled basket 
and stellate cell nuclei were scattered in the molecular layer. In other vermal 
lobules there was a significant but less dense label than in the nodulus and 
ventral uvula. Generally, the extent of c-fos labeling of molecular layer 
interneurons was in relation to nuclear labeling of granular layer neurons: 
labeling of both basket and stellate cells accompanied nuclear labeling of 
neurons throughout the depth of the granular layer, whereas only stellate cells 
were labeled when nuclear labeling was restricted to the superficial granular 
layer. Yaw horizontal or roll vertical rotations each stimulated c-fos 
expression in the cat medial vestibulo-cerebellum to approximately the same 
extent. Low-velocity rotations resulted in much less c-fos expression. Similar, 
albeit less intense, patterns of c-fos activation were observed in monkeys. 
Concentrated c-fos expression in the medial vestibulo-cerebellum after exposure 
to a strong head velocity signal that could originate from either otolith or 
canal excitation suggests that granule and unipolar brush cells participate in a 
neuronal network for estimating head velocity, irrespective of the signal 
source.