Search strategies on a hole-board are impaired in rats with ventral tegmental damage: animal model for tests of thought disorder.

An ability to distinguish relevance from irrelevance has been attributed to an attention-related mechanism and may be disturbed in thought-disordered schizophrenics. Stimulus choice strategies depend on such mechanisms (ia) and are anomalous in some schizophrenics. An impaired function of the ventral tegmentum (VTA) has been postulated for schizophrenia. The effects of VTA damage on the relevance/irrelevance distinction and strategy formation in rats has been studied. Over a 5 day-period food-deprived rats were given nine sessions of ten trials each on a 16-hole board. They searched for food pellets placed consistently in four holes. During testing the control group (C) reduced the number of empty holes visited more than the group with VTA damage. The proportion of repeated visits to relevant holes (had food) to irrelevant holes (never had food) increased for the C but not for the VTA group. The frequency with which a preferred sequence of food-hole visits was repeated during a session increased over sessions for the C but not the VTA group. The VTA group changed their preference between sessions more often. Animals with VTA damage were capable of simple learning, but were impaired when complexity increased. This may be due in part to a deficit in attention-related mechanisms. This encourages further study of the contribution of the VTA to putative attentional dysfunction and the use of the hole-board search task as a model for the study of cognitive function and dysfunction.