THE CEREBELLUM IN THE SPATIAL PROBLEM-SOLVING - A CO-STAR OR A GUEST STAR

The experimental findings reviewed here indicate that the cerebellum h as to be added to the regions known to be involved in the spatial lear ning. Cerebellar function is specifically linked to 'how to find an ob ject' rather than 'where the object is in the space'. In the Morris wa ter maze (MWM) hemicerebellectomized (HCbed) rats displayed a severe i mpairment in coping with spatial information, displaying only peripher al circling. And yet, when the MWM cue phase was prolonged, HCbed rats succeeded in acquiring some abilities to learn platform position, eve n in a pure place paradigm, such as finding a hidden platform with the starting points sequentially changed. Conversely, whether the searchi ng strategy was acquired preoperatively, no exploration deficit appear ed. Thus, cerebellar lesions appear to affect the procedural component s of spatial function, sparing the declarative ones. When intact anima ls were non-spatially pre-trained and then HCbed, they exhibited an ex panded scanning strategy, underlining the cerebellar involvement in pr ocedural component acquisition. By testing HCbed rats in an active avo idance task, first without and then with a request for right/left disc rimination, lesioned rats displayed severe deficits. Thus, besides a m arked impairment in facing procedural components of spatial processing , cerebellar lesion provokes deficits also in right/left discriminatio n task. In conclusion, it is possible to propose the cerebellum as one part of a large system that includes frontal, posterior parietal, inf erior temporal cortices, hippocampus and basal ganglia. These structur es form an allocentric spatial system and an egocentric control system , that interlock to process the information involved in representing a n object in the space. (C) 1998 Elsevier Science Ltd. All rights reser ved.