Cerebellar Damage Loosens the Strategic Use of the Spatial Structure of the Search Space

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The influence of a hemicerebellar lesion on the exploration of environments with different spatial distributions of multiple rewards was analyzed. Hemicerebellectomized (HCbed) and intact rats were submitted to a search task in which they had to explore nine food trays in an open field, avoiding repeated visits. Trays were spatially arranged in four configurations: cross, 3 x 3 matrix, circle, and three clusters of three trays each. Lesioned and intact rats' performances improved in all configurations used. However, the explorative activity of the HCbed animals differed from that of intact rats. Lesioned animals spent more time, made more errors, displayed lower search efficiency, exhibited shorter final spans, and traveled longer distances. They tended to perseverate and to neglect some trays. The cerebellar damage differentially influenced performances as a specific effect of the susceptibility of the configurations to being explored in a principled way. In the cross configuration that had strong spatial constraints, both groups made their lowest number of errors. In the circle configuration, the altered explorative strategies of lesioned animals made extremely demanding the acquisition of the task of searching multiple rewards, in spite of the attempt of favoring their altered procedures through an appropriate spatial arrangement. Since the procedural impairment elicited by cerebellar damage affected the central exploration, the matrix configuration was the most difficult configuration to be explored by the HCbed rats. The poor performances in the cluster configuration indicated that chunking was a strategy of relative strength in rats in general and in HCbed rats in particular.