Behavioural brain research
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The present study investigated whether spatial performance in the Morris water maze (MWM) recovers after bilateral transection of the fimbria/fornix (FF) in rats, whether such recovery results from restored or residual spatial cognitive capacity, and what contribution, if any, pre-operative training makes to such recovery. Following surgery, rats were administered extensive training to a constant submerged platform location with frequent probe tests to assess performance strategies. Following the attainment of asymptotic performance levels, rats were tested for acquisition of a second platform location. ⋯ The deficit shown in acquisition of the second platform location argues against recovery of spatial cognition and suggests that the basis of recovered performance is residual spatial cognitive capacity. Several limitations of this residual capacity are apparent: (i) rate of acquisition of spatial information is reduced; (ii) utilization of spatial information stored pre-operatively is restricted; and (iii) translation of spatial information into navigational behaviour is less efficient. The neural bases of this residual system are speculated to include spared intra-hippocampal storage mechanisms and/or mechanisms involved in extra-hippocampal long-term memory consolidation while the neural bases of the FF's contribution to spatial information storage in the intact brain are speculated to involve theta synchronization of hippocampal activity and the induction and expression of hippocampal long-term potentiation.