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H Mahut

Publications and source records attributed to H Mahut.

9 recordsLinked to original sources
PubMed1983

Enhanced preference for perceptual novelty in the monkey after section of the fornix but not after ablation of the hippocampus.

Previously uncovered discrepancies between the behavioral effects of fornix sections and hippocampal ablations in the monkey suggested that damage to the fornix but not that to the hippocampus may result in a motivational post-operative change. To test this notion, control monkeys and those with damage to either hippocampus or fornix were given an opportunity to choose freely between presentations of novel or repetitive stimuli in two modalities. In the visual mode, the choice was between viewing color slides which changed on every trial or repeated presentations of a geometric pattern (experiments 1 and 1a). In the auditory mode, the choice was between trains of identical clicks and different sound patterns (experiments 2 and 2a). Monkeys with sections of the fornix, but not those with ablations of hippocampus, showed an abnormally marked preference for novel stimuli in both modalities, even when perceptual novelty was designed to compete unfavorably with food reward (experiments 1b and 2b). These findings (a) provide another instance of functional dissociation between the effects of fornix and hippocampal damage and caution against assuming safely that data obtained with sections of the fornix will always mirror the behavioral consequences of hippocampal ablations; and (b) suggest that the hippocampus of primates may participate in the mediation of cognitive-motivational aspects of behavior which should be taken into account when the role of the hippocampus in memory processes is considered.

Animals↗
PubMed1982

Hippocampal resections impair associative learning and recognition memory in the monkey.

Damage to the hippocampus has been implicated in the permanent loss of memory in patients with medial temporal lobe resections. In two previous studies, it was established that bilateral ablations of the hippocampus in the monkey impaired performance on an associative learning task and on an object discrimination retention task. The two objectives of the present study were to assess the long term effects of hippocampal resections in the monkey and to extend the analysis of the effects of these resections to recognition memory. Therefore, the performance of monkeys with either hippocampal ablations or fornix transections, sustained 5 years earlier, was compared (1) on a concurrent discrimination task--a previously unencountered associative learning task--and (2) on a nonmatching-to-sample recognition task with either delays interposed between the presentation of the sample object and the recognition trial or with lists of either 1-, 3-, 5-, or 10-object samples. Significant impairment on both tasks was found after hippocampal, but not after fornix, damage. Though monkeys in the hippocampal group were impaired on both delays and lists, the impairment was more severe on the lists, with abnormal sensitivity to pro- and retroactive interference as a possible source of difficulty. Thus, in parallel with clinical findings, ablations of the hippocampus in the nonhuman primate produce an enduring disruption of memory.

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PubMed1981

Concurrent discrimination learning of monkeys after hippocampal, entorhinal, or fornix lesions.

Ablations of anterior inferotemporal cortex in monkeys are known to impair learning when discriminations between members of several pairs of objects are taught concurrently. This deficit has been attributed to a loss of visual mnemonic functions. But ablations of hippocampus have also been shown to impair retention, and this impairment transcends the visual modality. Therefore, in the first of two experiments, we compared the behavioral effects of inferotemporal cortical lesions with those of either hippocampus, entorhinal area, or fornix, using a visual concurrent discrimination task. Monkeys with either hippocampal or entorhinal ablations were impaired, while those with fornix sections were not. However, ablations of hippocampus included inadvertent damage of the inferotemporal cortex. Therefore, in the second experiment, behavioral effects of inferotemporal lesions were compared with those of hippocampus (without additional inferotemporal damage) on the concurrent task in both visual and tactual modalities. In the visual mode, monkeys with hippocampal removals were as impaired as those with inferotemporal ablations. In the tactual mode, however, hippocampal, but no inferotemporal, ablations were followed by a deficit. Our results, taken together with other existing evidence, emphasize the role of the hippocampus in mediating associative learning in more than one modality. These results, obtained with non-human primates, are in line with clinical findings.

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PubMed1976

EEG correlates of acquisition and extinction of expectancy.

The work to be described was begun in 1958 at the Montreal Neurological Institute in order to verify some of the prevailing neurophysiological notions concerning the mechanisms of habituation and attention. The results dealing with the EEG correlates of habituation and acquisition of expectancy were presented at the annual meetings of the American Psychological Association (Mahut 1959). Beginning in 1960 other authors started questioning the validity of the claims regarding mechanisms of attention that had been previously reported in the physiological literature. I hesitated, therefore, to publish my data. Professor Konorski, however, kindly urged me to do so, particularly the results concerned with the EEG of extinction and the effects of arousal on cortical electrophysiology. It is to his memory that this report is dedicated.

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