Cerebellar contribution to spatial event processing: characterization of procedural learning

Recently, we demonstrated the prevalent role of cerebellar networks in the acquisition of the procedural components of spatial information by testing hemicerebellectomized (HCbed) rats in a classical spatial task, the Morris water maze (MWM). As procedures used in the water maze are a mixture of dif ferent components (that is, general procedures, exploration procedures, dir ect reaching procedures), for optimally solving a spatial task all procedur al components must be opportunely managed. Thus, severely impaired procedur al learning of cerebellar origin can be better comprehended by fractionatin g the procedural facets. To this aim, a two-step water-maze paradigm was em ployed. Normal rats were first trained to search for a hidden platform move d to a different position in each trial, utilizing a water maze setting in which visual cues were abolished by heavy black curtains surrounding the ta nk. In this paradigm, normal animals solved the task by using general and e xploration procedures, but they could not use direct reaching skills. A sub group of these pretrained animals was then HC-bed and, after recovery from cerebellar lesion, was tested in a water maze with normal environmental cue s available, a paradigm in which normal animals develop abilities for reach ing the target with very direct trajectories. Pretrained HCbed animals, how ever did not display the typical spatial deficits of naive HCbed rats, pers isted in exhibiting the scanning strategy learned during pretraining, and n ever displayed direct reaching skills. In conclusion, cerebellar networks a ppear to be involved in the acquisition of all procedural facets necessary for shifting behavior within the maze until direct reaching of the platform . The lack of flexibility in changing exploration strategies displayed by p retrained HCbed rats is interpreted by taking into account the well-known c erebellar frontal interplay sculpting a specific cerebellar role in the acq uisition of spatial procedural steps.