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

Abstract

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.

Exposure to an Enriched Environment Accelerates Recovery from Cerebellar Lesion

“…Extensive anatomo-functional connections [62] support the interplay between the cerebellar and frontal areas that interact in executive control of voluntary behavior [63][64][65]: the cerebellum permits acquisition of efficient procedural competencies and the frontal cortex provides flexibility among already acquired and stored solutions [66][67][68]. Previously, we demonstrated that in rats HCb provokes lack of flexibility in changing strategy, impossibility to inhibit patently wrong responses [69][70][71], deficits due to impairment in adapting behavior to context. The evidence that the EH animals displayed no "frontal-like" deficits as perseverations and lack of attention to novel stimuli, as well as no deficient working memory, could be an index of an efficient use of cerebello-frontal networks.…”

Explorative function in Prader–Willi syndrome analyzed through an ecological spatial task

“…An environment organized in clusters allows to be explored with the possibility of chunking it, first visiting the locations within the same cluster and then moving to another one. The ''chunking theory'' predicts that once the chunks have been explored the burden on memory should be lightened from the total number of buckets to be explored (in our case, nine) to the number of clusters constituting the search space (in our case, three) (Foti et al, 2007(Foti et al, , 2010. Thus, the hierarchical organization of memory afforded by chunking substantially reduces the working memory load and promotes higher level performances (Terrace & McGonigle, 1994).…”

“…Efficient strategies for exploring the Matrix configuration are structured search patterns that follow rows (or columns) sequentially or, conversely, that travel the perimeter of the external ''square'' to reach the most internal bucket at the end. When the strategic use of these searching patterns is loosened, a compromise between an explorative behavior promoting an extended search among rewarded buckets (i.e., visiting buckets farther away than those previously visited or following diagonal trajectories between buckets) and a behavior that limits the information to be stored (i.e., visiting the nearest bucket) may be used (Foti et al, 2007(Foti et al, , 2010.…”

“…Traveling on, the subject re-encounters the central bucket that can be correctly skipped only in the case of an already formed cognitive spatial map and of effective working memory functions. Thus, the exploration of the Cross configuration is a challenging task that requires both procedural (change of strategy) and mnesic (memory load) components (Foti et al, 2007(Foti et al, , 2010. The PWS participants obtained performances worse in comparison to the TD children.…”

“…In this spatial test the subject is free to move putting into action exploratory behaviors that should adapt to the environment features. Thus, the environmental affordances influence the construction of the search strategies as well as the knowledge on where the rewards are (Foti, Spirito, Mandolesi, Aversano, & Petrosini, 2007;Foti et al, 2010;. Namely, in the present study the participants had to explore an open space to search nine rewards hidden in buckets arranged according to three spatial configurations: a Cross, a 3 Â 3 Matrix, a Cluster composed by three groups of three buckets each.…”