Effects Of Hippocampectomy Research Articles

Effects of hippocampectomy on the development and recovery of a conditioned reflex to time in rats.

Experiments were carried out on rats to study the dynamics of recovery of a conditioned reflex to time after electrolytic lesioning of the dorsal hippocampus and the effects of hippocampectomy on the development of this response. Lesioning of the hippocampus deranged the restoration of a conditioned reflex to time which had been fixed before surgery. In conditions of limited hippocampal damage, the conditioned reflex to time recovered earlier than in sham-operated animals. Animals with more significant damage showed delays in the recovery of the response to time. After hippocampectomy without initial training, the conditioned reflex to time could not be developed regardless of the extent of damage to the hippocampus. This process was also not affected by doses of phenamine of 0.05 mg/kg.

The effects of hippocampectomy on performance by rats of a running recognition task using long lists of non-spatial items

Unoperated rats, or rats with cortical control lesions or hippocampal aspiration lesions, were trained on a non-spatial delayed non-matching-to-sample task. Once the non-matching rule had been learned, the task was modified so as to assess list memory, with list lengths of up to 32 items. Hippocampectomy induced a significant drop in choice accuracy, that was independent of list length; nonetheless, hippocampectomised rats still performed at better than chance levels. The cortical control lesion appeared to induce an intermediate (though generally non-significant) deficit. It was concluded that hippocampectomy leaves rats still capable of choosing with considerable accuracy on non-spatial working memory tasks that use trial-unique or ‘pseudo-trial-unique’ stimuli, even under experimental conditions in which a heavy memory load is imposed.

Seemingly discrepant data from hippocampectomized macaques are reconciled by detectability analysis.

Wide differences in the effects of hippocampectomy on the visual memory performances of monkeys have been reported in the literature. These differences have been attributed to the extent of preoperative training. Previous calculations, however, have always utilized data expressed as a percentage correct. A reanalysis based on detectability, the d' of signal detection theory, suggests that the differences may be illusory. The losses in visual memory performance due to hippocampal lesions as measured in different laboratories are about equal in terms of d'. This points out a potential trap in making direct comparison of absolute differences in percentage values.

Differential effects of hippocampectomy on classically conditioned rabbit nictitating membrane response related to interstimulus interval.

The effects of hippocampal ablation on acquisition rates and temporal characteristics of classically conditioned nictitating membrane responses were examined in groups of rabbits trained with a 150-, 300-, or 600-ms interstimulus interval. Acquisition rates were accelerated in the 150- and 600-ms groups. No effect was present in the 300-ms group. Response onset latencies were also affected in the 150-ms group. These findings were interpreted to support the notion that the hippocampus modulates learned motor behavior by a neural model of the response to be executed.

The effects of hippocampectomy and of fimbria section upon the partial reinforcement extinction effect in rats.

Rats were trained to run in an alley for food reward given on every trial (continuous reinforcement, CR) or on a random 50% of trials (partial reinforcement, PR) and were then extinguished. Sham-operated controls showed the usual partial reinforcement extinction effect (PREE), i.e., PR-trained animals were more resistant to extinction than CR-trained animals. The PREE was abolished by hippocampectomy, which increased resistance to extinction in CR-trained rats and decreased it in PR-trained rats. Bilateral fimbria section had no effect on resistance to extinction in either condition. These results are discussed in the light of theories of hippocampal function and the anatomy of septohippocampal connections.

Arm choices in a sunburst maze: Effects of hippocampectomy in the rat

Hippocampectomized, neocortically damaged and unoperated rats were tested for response dispositions in a sunburst maze following training over a fixed path. The arm choices of neocortically damaged and unoperated rats were significantly limited to two of six alternatives. Hippocampectomized rats exhibited random selection of alternatives and were significantly different from controls. The neocortically damaged and unoperated rats were retested under scopolamine and retained a normal nonrandom selection pattern suggesting that normal hippocampal function was not necessary for the retention of these response selections. In accordance with this hypothesis, hippocampectomized rats trained preoperatively and tested for postoperative retention also exhibited a non-random selection pattern similar to controls, but they differed significantly in exploratory behavior. Choice patterns were stable over retests in the three groups. These data are consistent with the theory that the hippocampus is crucial in the acquisition of normal spatial dispositions, however spatial information once acquired may be available in the absence of hippocampus.

Effects of hippocampectomy in a one-trial electroconvulsive shock paradigm

One hundred and twenty male hooded rats sustained massive hippocampal lesions, cortical ablations, or sham operations, and were pretrained for 5 consecutive days in a standard two-compartment passive avoidance box. Footshock-ECS training intervals of.5 and 30 sec were evaluated; control groups received ECS alone or footshock alone. Posttraining testing was conducted for 5 consecutive days, and activity levels were monitored both pre- and posttesting in an open field. Although the standard retrograde effects of ECS were replicated, the finding that memory in amnesic rats recovers with repeated posttraining testing was not substantiated. While hippocampectomized rats displayed enhanced open-field exploration and short step-through latencies, massive hippocampectomy, contrary to an earlier report, failed to attenuate the amnesic effects of ECS.

The effects of hippocampectomy on alternation behavior and response to novelty

Rats with hippocampal lesions, cortical lesions and unoperated rats were tested for maze activity, spontaneous alternation, food-reinforced alternation, perseveration of the alternation response, and response to a novel alley before and after training. The animals with hippocampal lesions were more active in the maze and deficient on spontaneous and food-reinforced alternation, compared with the animals with cortical lesions and normal animals. Further, the hippocampectomized rats did not perseverate the alternation response and failed to enter a relatively novel alley when tested after maze training. Animals in both control groups (cortical and normal) entered the novel alley with equal frequency on tests given both before and after maze training.

Delayed alternation in monkeys after removal of the hippocampus

Sixteen monkeys were tested on spatial delayed alternation following complete removal of the hippocampus. Eight were trained preoperatively while eight received training only postoperatively. The results indicate that the effects of hippocampectomy on delayed alternation are extremely variable. In some instances there is relatively little impairment; in others there is severe impairment. Individual differences appear to be an important factor in determining the severity of the impairment. Some of the possible sources of these individual differences are discussed.

Effects of hippocampectomy on consummatory behavior and movement-inhibition in rats

Abstract The daily food and water intake of hooded rats with small and large, bilateral lesions of the hippocampus as well as neocortical and sham-operated controls was measured for 16 days preoperatively and 60 days postoperatively. These same subjects were then tested in a continuous-trial passive-avoidance task. The results indicated that the hippocampectomized subjects did not consume any more food or water than did the operated control groups. Moreover, the hippocampal animals were not deficient, relative to the control subjects, in withholding a prepotent approach tendency to avoid a noxious stimulus. These results caution against an unequivocal acceptance of prevailing views implicating the hippocampus in the regulation of food and water consumption as well as certain response-inhibition debilities.