Working memory theory of hippocampal function needs qualification

To compare the predictive value of "cognitive map" and "working memory" theories of hippocampal function, the performance of rats with dorsal hippocampal lesions was compared to that of control rats in a series of experiments. In Experiment I, experimental rats learned a spatial alternation task with normal ease, but in Experiment II, they were significantly impaired on an elevated 8-arm radial maze. In Experiment III, the performance of the same experimental and control rats was compared on two versions of a 16-arm enclosed radial maze. In the first version, carpet inserts served as cues to mark eight unbaited arms and each of the remaining arms contained one food pellet. While both experimental and control rats successfully avoided the set of cued arms, experimental rats reentered uncued baited arms more frequently than did control rats. In the second version no intramaze cues were provided, but the spatial distribution of baited and unbaited arms remained the same as that used in the first version. In this uncued version, experimental rats both entered unbaited arms and reentered baited arms more frequently than did control rats, i.e., they were impaired in both "reference" and "working" memory. These findings are compatible with the hypothesis that hippocampal lesions result in an impaired capacity to form cognitive maps but they are not compatible with the working memory hypothesis. Furthermore, twelve separate evaluators classed experimental rats as using fewer mapping and more orientation strategies than control rats in the 8-arm maze.     

Specification of direction and duration during programming of discrete sliding movements

Summary Two experiments on duration programming of a discrete sliding movement in choice reactions are reported. In the first experiment it was examined whether duration of movement might be preprogrammed when varied across sessions. The result suggested that programming of movement duration is dependent on direction uncertainty. Experiment 2 used the movement precue technique in an attempt to further examine programming of movement duration and direction. Movement duration, movement direction, movement form and foreperiod duration were manipulated. When duration was not precued, a duration effect was found, while precueing resulted in disappearance of the duration effect, demonstrating that duration of sliding movements can be preprogrammed. Moreover, (pre)programming duration was independent of direction uncertainty, supporting an independent order notion of programming of these response variables. Evidence that motor preparation comprises different processing stages was derived from the additive effects of foreperiod duration and of the movement variables duration and direction.