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D Gaffan

Publications and source records attributed to D Gaffan.

At least 73 records · Page 4Linked to original sources
PubMed1991

The role of monkey inferior parietal cortex in visual discrimination of identity and orientation of shapes.

Three cynomolgus monkeys (Macaca fascicularis) were tested for their visual learning ability following bilateral lesions to the inferior parietal cortex. In discrimination learning with patterns differing from each other in form and colour their performance was normal. In discriminating monochromatic patterns their performance depended on the nature of the pattern discrimination; when the discriminanda were different shapes (e.g. x,v) they performed well, while with discriminanda which differed only in the orientation of the shape (e.g. p,d) they performed relatively badly. These results were compared to the previously reported results of normal animals and animals with inferior temporal lesions performing the same task. The ratio of errors in orientation discrimination to errors in shape discrimination was significantly higher than normal in the group with parietal lesions, and significantly lower than normal in the group with inferior temporal lesions. These results suggest that the roles of inferior temporal and inferior parietal cortex in the discrimination of shape and orientation are complementary.

Animals↗
PubMed1991

Hippocampus and the blood supply to TE: parahippocampal pial section impairs visual discrimination learning in monkeys.

In the base of each temporal lobe in 4 monkeys (Macaca fascicularis) we sectioned the pia mater in an antero-posterior line along the most medial part of the inferior temporal visual association cortex (area TE), lateral to the parahippocampal cortex. This pial section interrupts the blood flow in branches of the posterior cerebral artery which cross the parahippocampal gyrus en route to area TE. Histologically, the brains of 2 of these animals did not show any abnormalities in cresyl violet stained material, apart from the small cortical damage along the line of the pial section itself. Of the remaining two animals, one had a small unilateral infarct in TE and one had bilateral infarcts in TE. All of these animals were impaired in visual discrimination learning, and the severity of impairment was correlated only imperfectly with the severity of infarction. These results show that pial section along the medial boundary of area TE can affect visual discrimination learning without producing large infarcts. Further, since aspiration lesions of the hippocampal formation require the pia mater to be sectioned in a similar way to that reported here, the effects of such aspiration lesions on visual learning and memory may be mediated in part by effects on TE.

Animals↗
PubMed1991

Amygdalectomy and ventromedial prefrontal ablation produce similar deficits in food choice and in simple object discrimination learning for an unseen reward.

Cynomolgus monkeys (Macaca fascicularis) with either bilateral amygdalectomy or bilateral ventromedial prefrontal cortical ablations showed abnormal choices between apple, lemon, olive, and meat. Not only did they choose meat or olive more often than normal animals, but also their choices were less consistent from trial to trial than the normal animals' choices were. The same animals were subsequently tested for their ability to learn 2-choice simultaneous visual discriminations between objects which they could suck. The positive object yielded fruit juice, which entered the mouth directly without being seen. Both groups of animals with lesions were severely impaired in this discrimination learning task. The reason why amygdalectomy has little effect on simple object discrimination learning in the Wisconsin General Test Apparatus, we suggest, is that the animal can there associate the visual discriminanda with the visual properties of the food reward, a mechanism which is not available when the reward is unseen. These results add to existing evidence of a close functional relationship between the amygdala and the ventromedial prefrontal cortex, and they support the proposal, derived from previous work, that the amygdala is important for associating visual stimuli with the incentive value of reinforcers.

Amygdala↗
PubMed1991

Amnesia following damage to the left fornix and to other sites. A comparative study.

Two memory-impaired patients, who had suffered damage to the left or both fornix columns during removal of a ventricular cyst, were compared with 3 others having left-sided hippocampal or thalamic lesions, and with normal controls. The tests used were nonverbal--scene recognition, delayed matching-to-sample and concurrent pattern and object discrimination learning. The last two are differentially sensitive to fornix transection and to hippocampal or thalamic ablations in monkeys; however, the patients with fornix damage did not show a distinctive pattern of impairment. The reasons for this discrepancy are discussed. The study adds to the evidence that fornix transection can cause wide-ranging memory disturbances in man.

Adult↗
PubMed1991

Auditory-visual associations, hemispheric specialization and temporal-frontal interaction in the rhesus monkey.

Monkeys (Macaca mulatta) learned preoperatively to associate each of 6 auditory stimuli with 1 of 6 visual stimuli. Ablation of the left prefrontal cortex in a group of 3 monkeys produced a substantial impairment in performance of the task, though performance was still above chance. Ablation of the right prefrontal cortex in a second group of 3 monkeys was without effect. Subsequently the superior temporal gyrus (auditory cortex) was removed in each animal unilaterally in the hemisphere contralateral to the existing prefrontal ablation. Ablation of the left auditory cortex produced a severe impairment, but ablation of the right auditory cortex was without effect. Finally, forebrain commissurotomy in the animals with left prefrontal and right temporal ablation reduced their performance virtually to chance level. These results are consistent with previous findings indicating a left hemisphere specialization for audition in the monkey, and they give strong support to the idea, derived from previous experiments on difficult associative learning in the monkey, that auditory-visual association depends on a convergence of auditory and visual information in the prefrontal cortex.

Animals↗
PubMed1991

Amnesia in man following transection of the fornix. A review.

Published accounts of the effects of fornix damage on memory in man are critically evaluated. Most weight is given to cases of surgical transection of the fornix, though other causes of fornix damage are briefly discussed. It is concluded that fornix transection causes amnesia.

Amnesia↗
PubMed1990

Interhemispheric transfer of visuomotor conditional learning via the anterior corpus callosum of monkeys.

Two experiments examined interhemispheric transfer of learning across the anterior corpus callosum in monkeys (Macaca fascicularis). The animals learned a series of visuomotor conditional discrimination problems for food reward. Within each problem the animals were first trained using one hand to make the motor responses, and were then required to use the opposite hand in order to test for intermanual transfer of the initial learning. In Exp. 1, a group of animals with surgical section of the entire corpus callosum and anterior commissure showed a complete absence of intermanual transfer of learning. A second group, in which only the anterior commissure and the posterior part of the corpus callosum were sectioned, leaving the anterior corpus callosum intact, showed good intermanual transfer. Thus, intermanual transfer in the second group represented interhemispheric information transfer via the anterior portions of the corpus callosum. However, in Expt. 2, normal intermanual transfer was seen in a group of animals in which the anterior corpus callosum alone had been sectioned. We conclude that the anterior corpus callosum can mediate interhemispheric transfer of visuomotor conditional learning, but is not the only available route for such transfer in the present task.

Animals↗
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↗
PubMed1990

Amygdalar interaction with the mediodorsal nucleus of the thalamus and the ventromedial prefrontal cortex in stimulus-reward associative learning in the monkey.

Cynomolgus monkeys (Macaca fascicularis) were assessed for their ability to associate visual stimuli with food reward. They learned a series of new 2-choice visual discriminations between colored patterns displayed on a monitor screen. The feedback for correct choice was the delivery of food. In order to promote associative learning between the visual stimuli and the incentive value of the food reward, reward delivery was not accompanied by any distinctive visual feedback on the display screen. The rate of learning new problems was assessed before and after surgery in a total of 16 monkeys. Three groups of 3 monkeys received bilaterally symmetrical ablations in either the amygdala, the mediodorsal nucleus of the thalamus, or the ventromedial prefrontal cortex. All these groups showed a severe postoperative learning impairment. Seven other animals were given a unilateral ablation in 1 of those 3 structures and a second unilateral ablation, in each case contralateral to and different from the first, in order to produce 2 groups in which a putative amygdalo-thalamo-prefrontal pathway had been disconnected by crossed unilateral lesions. One disconnection group had lesions in the amygdala and ventromedial prefrontal cortex; the other had lesions in the amygdala and the mediodorsal nucleus of the thalamus. The disconnection groups showed a significant impairment, but the effect of the disconnection surgeries was significantly milder than the effect of any of the 3 bilaterally symmetrical lesions. Therefore, symmetrical bilateral lesions in either the amygdala, the mediodorsal nucleus, or the ventromedial prefrontal cortex produce similar impairments in the present task, implying that these structures are functionally related to each other; but the relatively mild effect of disconnecting these structures from each other argues against the hypothesis that they are serial stages in a single, tightly linked functional pathway.

Amygdala↗
PubMed1989

A comparison of the effects of fornix transection and sulcus principalis ablation upon spatial learning by monkeys.

In each of three experiments with Cynomolgus monkeys (Macaca fascicularis), there was a group of normal control animals, a group with bilateral cortical ablations in the principal sulcus, and a group with fornix transection. In Expt. 1, half of each group learned problems in which the position of a pair of visual stimuli, to the monkey's left or right, indicated which of the visual stimuli was the correct (rewarded) one. The other animals learned problems in which visual stimuli indicated, irrespective of their own spatial position, whether reward was to be found on the monkey's left or on the right. The animals with fornix transection were impaired in both tasks. The animals with sulcus principalis ablation were also impaired in both tasks. The impairment caused by fornix transection was more severe than that caused by sulcus principalis ablation. Within each of the two operated groups, the degree of impairment in the two tasks was equal, when assessed in proportion to the difficulty of each task for control animals. Expt. 2 showed that neither of the operated groups was impaired in visual discrimination learning with spatial position irrelevant. Expt. 3 tested spatial discrimination learning (acquisition and reversal of a left-right discrimination) with irrelevant visual cues. Here the fornix-transected group was impaired but the group with sulcus principalis ablations was normal. It is suggested, on the basis of these findings and previous results, that fornix transection produces a general deficit in remembering the spatial arrangement of whole scenes, while sulcus principalis ablation produces a deficit in high-order integration involving spatial information.

Animals↗
PubMed1989

Effects of fornix transection and cingulate cortical ablation on spatial memory in rhesus monkeys.

This study, together with a parallel study in rats (Markowska et al. 1988), attempted to relate the effects of hippocampal-system damage on similar tasks in both rats and monkeys. Not only were monkeys given a task (Experiment 1) which was of the sort usually used with rats, but in the companion study rats were given tasks (Experiment 2) like those usually used with monkeys. Experiment 1 examined the performance of rhesus monkeys with hippocampal-system damage on a spatial working memory task. Monkeys were trained preoperatively on delayed nonmatching-to-sample in a T-maze, placed into groups matched for their preoperative learning scores, and then received one of three treatments: 1) transection of the fornix; 2) ablation of the cingulate cortex; or 3) a sham operation. Monkeys with fornix transection were severely and significantly impaired, but monkeys with cingulate cortical ablations were not significantly impaired, relative to the controls. The results demonstrate that monkeys with fornix transection are severely impaired on a spatial working memory task requiring locomotion and, taken together with earlier work, suggest that the effect of fornix transection in both rodents and nonhuman primates is at least qualitatively similar (see Markowska et al. 1988). Experiment 2 assessed the role of the fornix and cingulate cortex in three conditional tasks in which the monkeys were provided with various spatial cues to indicate which one of two objects was rewarded. Both experimental groups were unimpaired, relative to the control group, on all three tasks, indicating that fornix transection does not produce a general impairment in place learning.

Animals↗
PubMed1989

A comparative analysis of the role of fornix and cingulate cortex in memory: rats.

In order to compare the role of the fornix (FX) and cingulate cortex (CC) in memory, rats were trained in a series of discriminations using procedures that were the same as those used for monkeys (Murray et al. 1986, 1988). A spatial delayed nonmatching-to-sample (DNMS) discrimination tested recent memory for spatial location in a T maze using interrun intervals (IRI) that varied from 5 s to 15 min. FX and CC lesions produced a substantial impairment in the performance of this task during postoperative testing. Three conditional discriminations (CD) followed. In each one, the rat was presented with two objects, only one of which was correct. The nature of the conditional stimuli changed in each discrimination: the place of the maze in the room; the direction that the rat moved to approach the objects; the side (left or right) to which the rat turned. Control rats learned all three types of conditional discriminations. FX and CC lesions did not impair choice accuracy. In a subsequent repetition of the spatial DNMS procedure, FX and CC lesions again produced a substantial impairment, indicating that the lack of an impairment in the three CDs was not due to recovery of function. These data indicate that the hippocampal system and its connections through the fornix are importantly involved in spatial working memory in both rats and monkeys, and that the CDs do not require this type of memory. The results are discussed in the context of different theories of the brain mechanisms involved in memory.

Animals↗
PubMed1989

Place memory and scene memory: effects of fornix transection in the monkey.

Five experiments examined the effects of fornix transection upon some spatial and visual learning tasks in monkeys (Macaca fascicularis). For each trial of each task, the monkey was brought to a test tray and allowed to choose between 2 objects on the tray. In different tasks, different cues were provided by the experimenter to guide the monkey's choices. In total 5 different tasks were run (Experiments 1 to 5) and the results showed that the effects of fornix transection varied markedly between tasks: the animals with fornix transection were severely impaired in experiments 1, 3 and 5 but learned normally in experiments 2 and 4. It is concluded that the results cannot be explained by the simple hypothesis of a deficit in place learning, since some forms of place learning are unimpaired by fornix transection. A better general hypothesis is that the memory disrupted by fornix transection is like a snapshot memory, which stores the spatial arrangement of items in a witnessed scene.

Animals↗
PubMed1989

Interhemispheric transfer of visual learning in monkeys with intact optic chiasm.

The purpose of the present experiments was to investigate the role of the forebrain commissures in interhemispheric visual transfer when both eyes are open and the optic chiasm is intact. Cynomolgus monkeys (Macaca fascicularis) learned a series of two-choice simultaneous visual discriminations. The visual stimuli were bipartite, with independently determined left and right halves. If such a stimulus is fixated centrally, the two halves fall into opposite visual hemifields. After 10 trials of acquisition of each discrimination, the same discriminanda were presented for a further 10 trials in which, within each stimulus, the positions of the halves were exchanged: the left half became the right and vice versa. The unoperated animals transferred well to the altered stimuli, making many fewer errors than they made in learning the originally presented discrimination. In contrast, monkeys with section of the posterior corpus callosum and the anterior commissure transferred poorly. These effects show that the forebrain commissures are important for the interhemispheric transfer and integration of visual information in animals with a normal, intact peripheral visual system.

Animals↗
PubMed1989

Projections from inferior temporal cortex to prefrontal cortex via the uncinate fascicle in rhesus monkeys.

In five rhesus monkeys (Macaca mulatta) we used anterograde and retrograde tracing techniques to investigate the projection from the inferior temporal cortex (area TE) to the prefrontal cortex as well as the course of the projecting fibers. The results showed that TE projects to both the inferior convexity and orbital surface of prefrontal cortex and that these projections course almost exclusively via the uncinate fascicle. Transection of the uncinate fascicle deprives the prefrontal cortex of virtually all input from TE, but leaves intact inputs from prestriate and parietal visual areas as well as the amygdala. Such transection also leaves intact many projections from TE to targets other than the prefrontal cortex, including the amygdala, ventral putamen, tail of the caudate nucleus, and pulvinar.

Amino Acids↗
PubMed1989

Reaching to a rewarded visual stimulus: interhemispheric conflict and hand use in monkeys with forebrain commissurotomy.

Monkeys (Macaca fascicularis) learned simultaneous visual discriminations for food reward. Two coloured patterns were presented one above the other and the monkey chose one by touching it with a hand. On some trials, conflicting information was presented to the two visual hemifields. For example, in the left hemifield the stimulus associated with reward was in the higher position and in the right hemifield the stimulus associated with reward was in the lower position. On some of these conflict trials the monkeys were required to use the left hand and on others the right. Normal monkeys, monkeys with section of the anterior commissure and the posterior corpus callosum, and monkeys with section of the anterior commissure and the whole of the corpus callosum performed this task. Our aim was to test the hypothesis that following forebrain commissurotomy, the response made by each hand would be predominantly influenced by the visual information put into the hemisphere contralateral to that hand. If this is true then choices in the conflict test should vary systematically with hand use. This hypothesis was not confirmed. We conclude that when a monkey reaches to a rewarded visual stimulus, information about the reward history of the stimulus is integrated between the hemispheres before influencing the motor control of the hand that reaches, either by a peripheral or a subcortical route.

Animals↗
PubMed1989

Visual-visual associative learning and reward-association learning in monkeys: the role of the amygdala.

Three Cynomolgus monkeys (Macaca fascicularis) took part in an experiment on visual learning set in an automatic apparatus. Each new visual discrimination problem was solved using a visual secondary reinforcer consisting of a white line. If the monkey chose the correct stimulus (by touching it), the white line appeared over the correct stimulus. Primary food reward was delivered only after a new problem was solved to a criterion, and the problem was then replaced by a new one. Thus, within-problem learning did not rely on primary reinforcement but on the visual secondary reinforcer. The animals were trained preoperatively in visual learning set with this procedure and were assessed postoperatively for their ability to learn new visual discriminations with the same procedure. Bilateral amygdalectomy did not significantly impair the animals' learning ability in this task. Learning remained unimpaired when transection of the uncinate fascicle and of the fornix was added to amygdalectomy. The effect of bilateral amygdalectomy in this task was much less severe than in a similar task we previously studied, with auditory secondary reinforcers. The results show that the involvement of the amygdala in processes of secondary reinforcement depends on the sensory properties of the secondary reinforcer. From these and other recent results, we conclude that the sensory attributes of a reinforcer are easily associated with a discriminative stimulus when they are in the same modality and same spatial location as the discriminative stimulus and that this sensory-sensory association is independent of the amygdala.

Amygdala↗