The cerebellum in the spatial problem solving: a co-star or a guest star?

The experimental findings reviewed here indicate that the cerebellum has to be added to the regions known to be involved in the spatial learning. Cerebellar function is specifically linked to 'how to find an object' rather than 'where the object is in the space'. In the Morris water maze (MWM) hemicerebellectomized (HCbed) rats displayed a severe impairment in coping with spatial information, displaying only peripheral circling. And yet, when the MWM cue phase was prolonged, HCbed rats succeeded in acquiring some abilities to learn platform position, even in a pure place paradigm, such as finding a hidden platform with the starting points sequentially changed. Conversely, whether the searching strategy was acquired preoperatively, no exploration deficit appeared. Thus, cerebellar lesions appear to affect the procedural components of spatial function, sparing the declarative ones. When intact animals were non-spatially pre-trained and then HCbed, they exhibited an expanded scanning strategy, underlining the cerebellar involvement in procedural component acquisition. By testing HCbed rats in an active avoidance task, first without and then with a request for right/left discrimination, lesioned rats displayed severe deficits. Thus, besides a marked impairment in facing procedural components of spatial processing, cerebellar lesion provokes deficits also in right/left discrimination task. In conclusion, it is possible to propose the cerebellum as one part of a large system that includes frontal, posterior parietal, inferior temporal cortices, hippocampus and basal ganglia. These structures form an allocentric spatial system and an egocentric control system, that interlock to process the information involved in representing an object in the space.