Cerebellar contribution to spatial event processing: right/left discrimination abilities in rats.

Recently, we demonstrated the involvement of cerebellar circuits in the procedural components of spatial information processing by testing hemicerebellectomized (HCbed) rats in classical spatial paradigms, such as the Morris Water Maze and the water T-maze. Since procedural components are strongly present in these tests, an impairment also in processing more abstract spatial information, linked to 'where an object is' rather than to 'how to find it', could be hidden by the severe procedural deficits. On this basis, we investigated the influence of cerebellar lesions on spatial abilities strictly reducing procedural variables by employing an active avoidance task, first without and then with a request for right/left discrimination. In the two-way active avoidance task without spatial requests, controls and cerebellar operated rats developed active avoidance responses which were not statistically different, demonstrating that this kind of associative learning is not significantly affected by hemicerebellectomy (HCb). A second experimental group of cerebellar lesioned rats was tested in a modified version of this basic paradigm in which a right/left discrimination request was added. This group displayed severe deficits, which even in the last testing sessions prevented them from performing comparably to the control animals. Reversal of the rewarded choice, even if it affected the performances of both controls and operated rats in the first inversion trials, elicited the lowest number of correct responses in HCbed rats throughout the entire spatial reversal learning, suggesting a severe deficit in the ability to change an initially learned behaviour. These results demonstrate that, beside having a marked impairment in facing procedural components of spatial processing, cerebellar lesioned rats are severely defective also in right/left discrimination tasks, suggesting a role of cerebellar networks also in the discriminative spatial information processing.