Biomedical subjects

J P Aggleton

Publications and source records attributed to J P Aggleton.

At least 19 recordsLinked to original sources

PubMed1992

Removal of the hippocampus and transection of the fornix produce comparable deficits on delayed non-matching to position by rats.

Rats with radiofrequency lesions of the fimbria/fornix or with extensive aspiration lesions of the hippocampal region (the hippocampus proper, dentate gyrus, and subicular complex) were tested on their performance of a delayed non-matching to position task which had been learnt before surgery. On a given trial, one of two sample levers was presented in a random manner. Following a response on this lever and a subsequent delay, both levers were presented and reward was now contingent on a response on the lever that was not used as the sample. Both lesions produced equivalent performance deficits on this test of spatial working memory, the pattern of these deficits being consistent with a mnemonic impairment. The lack of difference between these two groups on a variety of performance measures indicates that hippocampal connections passing through the fornix are not only necessary for this test, but that non-fornical hippocampal connections appear unable on their own to maintain accurate responding.

Animals↗

PubMed1992

Lesions of the fornix but not the amygdala impair the acquisition of concurrent discriminations by rats.

Rats with lesions in either the fornix, the amygdala, or both were compared with control animals on the acquisition of three different concurrent object discrimination tasks. In the first task the animals received one trial per day on each of six pairs of stimulus objects ('spaced' condition). In the second task the animals received four trials per day on each of six stimulus pairs ('standard' condition), and in the last task the animals received 36 trials on each of two stimulus pairs in just a single day ('massed' condition). Animals with fornical lesions were impaired on all three conditions. In contrast, the amygdala lesions only affected the 'massed' condition and then only when the animals had to select the 'non-preferred' stimulus. Although animals with combined amygdala and fornical lesions were impaired on all three conditions there was no evidence that their deficit was greater than that in the animals with lesions restricted to just the fornix. In view of the evidence that concurrent discrimination learning offers an appropriate test for anterograde amnesia these findings are seen as consistent with the notion that the hippocampus, but not the amygdala, is critically involved in the mnemonic processes disrupted by amnesia.

Amygdala↗

PubMed1992

The performance of postencephalitic amnesic subjects on two behavioural tests of memory: concurrent discrimination learning and delayed matching-to-sample.

The performance of a group of three postencephalitic subjects with anterograde amnesia was examined on a series of concurrent visual discrimination problems and on a test of visual recognition, delayed matching-to-sample. These tests were chosen as they have been used to assess experimental models of anterograde amnesia in nonhuman primates. In comparison with a group of normal subjects the postencephalitic group were impaired on the more difficult concurrent discrimination problems. They also performed poorly on the matching-to-sample task when given lists of items to remember or given increased retention intervals. The pattern of performance of the postencephalitic group matched closely that of a group of Korsakoff subjects, indicating that these behavioural tests are equally sensitive to different types of anterograde amnesia.

Adult↗

PubMed1991

Both fornix and anterior thalamic, but not mammillary, lesions disrupt delayed non-matching-to-position memory in rats.

Rats with radiofrequency lesions of the fimbria/fornix, or neurotoxic lesions of the mammillary bodies or the anterior thalamic nuclei were tested on their ability to perform a delayed non-matching-to-position task that had been learnt before surgery. In this task rats had to respond to a sample lever in an operant chamber and, after a variable delay (during which they were required to respond at the magazine tray), press the other lever when both were presented. Extensive mammillary body lesions had no effect on performance. In contrast, lesions in either the anterior thalamic nuclei or the fimbria/fornix produced marked deficits, the pattern of these deficits being consistent with a mnemonic impairment. It is argued that the anterior thalamic nuclei represent an important hippocampal output for spatial problems, but that the mammillary bodies are only necessary for certain types of mnemonic task.

Animals↗

PubMed1991

Amygdaloid lesions and stimulus-reward associations in the rat.

Rats with amygdaloid lesions were trained on learning set tasks designed to tax stimulus-reward associations. Lesions centred in the medial and ventral half of the amygdala had no effect on the acquisition of two object discriminations but did impair successive reversals of the second discrimination. The same lesions had no effect, however, on the acquisition of a spatial win-stay lose-shift task which taxed one-trial place-reward associations. In a second experiment it was found that lesions in the central and basolateral regions of the amygdala disrupted performance of the same spatial win-stay lose-shift task although, as before, acquisition was unaffected. Taken together these findings support a role for the amygdala in stimulus-reward associations and indicate that it may be particularly important when differing values of reward must be distinguished.

Amygdala↗

PubMed1991

Transient impairment of recognition memory following ibotenic-acid lesions of the basal forebrain in macaques.

To assess the contributions of the basal forebrain cholinergic nuclei to visual recognition memory in macaques, we compared the effects of lesions of (a) the nucleus basalis of Meynert, (b) the medial septal and diagonal band nuclei, and (c) all nuclei combined on performance of delayed nonmatching-to-sample with trial-unique stimuli. Whereas monkeys with the separate lesions did not differ from each other or from normal control animals, those with combined lesions showed a significant impairment. With time and extended practice, however, the performance of the animals with combined lesions recovered to normal levels. During the recovery period, these monkeys showed an initially increased sensitivity to scopolamine that later dissipated, at which time they also failed to show the improvement that follows physostigmine administration in normal animals. Postmortem assessment of cortical choline acetyltransferase activity revealed that only the group with combined lesions had significant depletion of this enzyme. The results suggest that (1) the basal forebrain cholinergic system participates in mnemonic processes in primates and that (2) extensive damage to this system is necessary before impairments in recognition memory, even transient ones, can be observed.

Acetylcholinesterase↗

PubMed1991

Medial dorsal thalamic lesions and working memory in the rat.

Pigmented rats of the DA strain with either radiofrequency or ibotenic acid lesions of the thalamic nucleus medialis dorsalis were postoperatively given nonspatial and spatial tests of working memory. In the nonspatial task, delayed nonmatching-to-sample, rats with both types of thalamic lesions showed acquisition impairments. The subgroup of rats with nucleus medialis dorsalis lesions that were able to reach the acquisition criterion did, however, perform normally when the retention interval was extended to 60 s. In the spatial task, delayed forced-alternation, rats were tested with differing retention intervals and with both spaced and massed trials. Damage to nucleus medialis dorsalis had no effect on acquisition or on spaced trials, but a slight deficit was found in the animals with radiofrequency lesions under the massed trial condition. Much clearer deficits were, however, present in those animals in which the lesion extended appreciably into the anterior thalamic nuclei. The findings indicate that while cellular damage to nucleus medialis dorsalis may disrupt learning, some impairments in tests of spatial working memory attributed to this nucleus may reflect damage to the adjacent anterior thalamic nuclei.

Animals↗

PubMed1991

Occupation and handedness: an examination of architects and mail survey biases.

Handedness among architects was determined by mail survey. Contrary to previous reports, no evidence was found of an excess of left-handers among a sample of 236 fully qualified male architects and 78 male architectural students. A second study examined whether the use of mail surveys systematically biases the returns of handedness questionnaires. For this, questionnaires were sent to 1,017 university students. No evidence was found for a bias amongst those who did and did not reply to the initial questionnaire. These results strengthen the findings of the first study.

Architecture↗

PubMed1990

The effects of mammillary body and combined amygdalar-fornix lesions on tests of delayed non-matching-to-sample in the rat.

A series of experiments compared the effects of mammillary body lesions with those of combined damage to the amygdala and fornix on 2 tests of working memory, both of which used the delayed non-matching-to-sample rule. This comparison was based on evidence of the involvement of these regions in anterograde amnesic syndromes. The mammillary body lesions had no effect on the acquisition or subsequent performance of a non-spatial recognition task and had only a mild effect on the acquisition of a spatial forced-alternation task. Although the animals with combined amygdalar plus fornix lesions were able to master the non-spatial recognition task they were impaired when the levels of proactive interference were increased. The same animals were also severely impaired on the forced-choice alternation task. The overall pattern of results is seen as mirroring those found in primates and points to an underlying similarity in the mnemonic roles of these limbic regions.

Amygdala↗

PubMed1990

Visual impairments in macaques following inferior temporal lesions are exacerbated selectively by additional damage to superior temporal sulcus.

The present study examined the behavioural effects of removing the inferior temporal cortex (area TE) either on its own or in combination with the adjacent fundus and upper bank of the superior temporal sulcus (area STP). Comparisons with preoperative behaviour showed that the addition of superior temporal sulcal damage led to an increase in visual components of the Klüver-Bucy syndrome, i.e. an increased tendency to touch and examine objects coupled with a decrease in emotional reactivity, but no excessive orality, changes in food preference, or coprophagia. No group differences were found in the learning of 3 pattern discriminations, but the animals with additional superior temporal sulcal lesions were more impaired than the others on 3 colour discriminations, successive reversals of an object discrimination, and a learning-set task. These findings indicate that STP provides an important route, independent of the route via TE, by which visual information can reach limbic structures to evoke affective responses and contribute to visual learning.

Amygdala↗

PubMed1990

Cross-modal matching by amnesic subjects.

The present study examined the performance of two groups of amnesic subjects on a cross-modal identification task. It was found that subjects with Korsakoff's disease did not differ from alcoholic controls on their ability to match the tactile feel of an arc with the visual appearance of the full circle from which the arc was taken. The postencephalitic subjects were, however, impaired on this same task. All groups performed normally on two intramodal control tasks. The postencephalitic group, like the Korsakoff subjects, were also poor at identifying common objects from tactile cues. The results are consistent with the notion that limbic regions in the temporal lobe are important for cross-modal associations.

Adult↗

PubMed1990

Concurrent and sequential pattern discrimination learning by patients with Korsakoff amnesia.

Patients with Korsakoff's syndrome and alcoholic controls learned to discriminate sets of pairs of patterns presented concurrently, in order to test predictions based on monkeys' performance in similar tasks following medial temporal or diencephalic lesions. In Experiment 1 the subjects learned a 2-pair, a 6-pair and a 10-pair set; the Korsakoff group were impaired on the first and last, but not on the second set. In Experiment 2, the same subjects learned single pairs sequentially, and 2-pair and 8-pair sets concurrently. The effect of 2 types of feedback for correct responses (visual or non-visual) was also compared. The Korsakoff patients were markedly poorer than controls under all conditions; the type of feedback made little difference. In several respects the patients' impairment differed from what had been predicted from the animal experiments.

Alcohol Amnestic Disorder↗

PubMed1989

Effects of amygdaloid and amygdaloid-hippocampal lesions on object recognition and spatial working memory in rats.

Neurotoxic lesions of the amygdala did not affect the postoperative acquisition of a nonspatial test of object recognition (delayed nonmatching to sample) even when retention delays were increased from 0 s to 20 or 60 s, or when test stimuli were deliberately repeated within a session. Although these amygdaloid lesions did not alter forced-choice spatial alternation, they slightly increased neophobic responses to novel foods and environments. In contrast, combined amygdalohippocampal (A + H) lesions impaired performance on the object recognition task when the retention intervals were increased beyond 0 s and when test stimuli were repeated within a session. The A + H rats were also severely impaired on the spatial alternation task, and they showed reduced neophobia. Comparisons with a previous study show that damage to the amygdala or hippocampus does not affect object recognition, whereas A + H damage produces clear deficits.

Amygdala↗

PubMed1989

Working memory in aged rats.

The performances of young and aged rats were compared on a spatial (spatial delayed nonmatching-to-sample) and a nonspatial (object delayed nonmatching-to-sample) test of working memory. Although evidence was found that aging showed acquisition of both of these tasks, performance over different retention intervals of up to 60 s was normal once the task was mastered. An impairment was found, however, in the performance of the spatial test when the number of locations to be remembered on each trial was increased from one to two. The conclusions of this study are that under some conditions, the retention capabilities of aged rats may not change and that some acquisition impairments do not reflect alterations in learning or memory per se, but, in common with other studies, deficits in the remembrance of spatial locations may be found.

Aging↗

PubMed1989

Handedness in 'fast ball' sports: do left-handers have an innate advantage?

The study reported here examined whether left-handedness is an intrinsic advantage in three sports: cricket, tennis, and football (soccer). An analysis of cricket yearbooks showed that over the last four decades there was a relatively high proportion of professional cricketers who bowled left-handed. In contrast, an analysis of handedness in top batsman, as measured by bowling hand, failed to find any evidence of a handedness effect. Similarly, there was no clear, consistent excess of left-handed players among an overall sample of 500 male or 252 female professional tennis players or among 167 professional football goalkeepers. The latter group were of particular interest as left-handed goalkeepers are not tactically favoured by their relative rarity or by the symmetry of the sport. The most parsimonious explanation of the present findings is that any excess of left-handers in these sports is due to the nature of the game and not to any supposed neurological advantage.

Female↗

PubMed1988

The performance of amnesic subjects on tests of experimental amnesia in animals: delayed matching-to-sample and concurrent learning.

A group of amnesic Korsakoff subjects and a group of alcoholic controls were trained on a test of visual recognition, delayed matching-to-sample with trial unique stimuli. This test was modelled on comparable tasks used in the development of animal models of human amnesia. It was found that the Korsakoff subjects were severely impaired when the task difficulty was increased by lengthening the retention delay beyond 10 sec or by increasing the number of items intervening between sample presentation and test. The amnesic subjects were also impaired on the acquisition of a set of concurrent visual discriminations. These results bear clear similarities to those obtained from experimental amnesic syndromes in monkeys.

Adult↗

PubMed1987

Effects of scopolamine and physostigmine on recognition memory in monkeys with ibotenic-acid lesions of the nucleus basalis of Meynert.

Monkeys with bilateral ibotenic-acid lesions of the nucleus basalis of Meynert, an area rich in cholinergic neurons that innervate the cerebral cortex, were compared with unoperated control monkeys on a recognition memory task. Although animals with large lesions had substantial reductions of cortical choline acetyltransferase activity, none showed impairment in the task. Lesion effects were observed, however, when performance was assessed following administration of a muscarinic receptor blocker (scopolamine) or a cholinesterase inhibitor (physostigmine). Although scopolamine produced dose-related impairments in both groups, this effect was greater in the experimental animals. Conversely, whereas physostigmine produced modest improvement in performance in the control group, no such improvement was observed in the experimental animals. The altered sensitivity to the mnemonic effects of cholinergic agents in the experimental group suggests that the cholinergic neurons of the nucleus basalis of Meynert contribute to recognition memory.

Acetylcholinesterase↗

PubMed1987

A comparison between the connections of the amygdala and hippocampus with the basal forebrain in the macaque.

Autoradiographic experiments indicated that the amygdala projects to division Ch3 and Ch4 of the basal forebrain (nomenclature from Mesulam et al. 1983) and the olfactory tubercle. The heaviest of these amygdaloid outputs arose from the lateral basal, accessory basal, central, and medial amygdaloid nuclei, each with a slightly different pattern of distribution from that of the other. Injections of the retrograde tracer horseradish peroxidase (HRP) into the amygdala revealed dense reciprocal projections arising from region Ch4, especially from subdivisions Ch4al, Ch4iv, and Ch4p. The other basal forebrain regions, by contrast, provided very little input to the amygdala. Hippocampal efferents terminated densely in the medial (Ch1), lateral and dorsal septum, and in region Ch2. Hippocampal efferents terminated less densely in restricted portions of the olfactory tubercle and in Ch4. Experiments in which the fornix was transected showed that all of these hippocampal projections to the basal forebrain ran through the fornix. The hippocampal output to the septum, which was the heaviest projection of those examined, appears to have a crude topographic arrangement. Little overlap was observed between the terminal zones of the amygdaloid and hippocampal projections to the basal forebrain, indicating yet again the independence of the amygdaloid and hippocampal systems that has been demonstrated in other regions of the forebrain, such as the thalamus and cerebral cortex.

Amygdala↗