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D Gaffan

Publications and source records attributed to D Gaffan.

At least 91 records · Page 5Linked to original sources
PubMed1988

Inferotemporal-frontal disconnection and fornix transection in visuomotor conditional learning by monkeys.

The first 2 experiments examined the ability of monkeys (Macaca fascicularis) to learn a series of visuomotor conditional discrimination problems for food reward. In each discrimination problem there were 2 visual stimuli, which were different from those in any previous discrimination problem. Each trial within a problem presented either one visual stimulus or the other, and the stimulus indicated which of 2 motor responses, tap or hold, was correct; the motor responses were defined in such a way as to be mutually exclusive. Successive problems were each trained to a criterion of correct performance. In the first experiment, it was found that fornix transection did not impair monkey's learning rate in this task. This result contrasts with previous results showing an impairment of learning rate following fornix transection in visuo-motor conditional discriminations in which the 2 motor responses were differentiated from each other by their spatial position or direction. The present result shows that the earlier demonstrated impairments are specific to spatial responses. In the second experiment, learning rate in the present task was found to be impaired by the combination of a unilateral inferotemporal ablation, contralateral to the hand used in the task by the animal, with a transection of the anterior corpus callosum. This result suggests that cortico-cortical interaction between the inferotemporal area and the frontal lobe contralateral to the hand in use is necessary for efficient learning in this task. The third experiment examined simultaneous 2-choice visual discrimination learning in the animals which had participated in experiment 2. In contrast to the results of Expt. 2, learning rate in this task was unimpaired. Experiment 3 shows that the impairment observed in Expt. 2 is not a general impairment of visual learning.

Animals↗
PubMed1988

Disconnection of the amygdala from visual association cortex impairs visual reward-association learning in monkeys.

Cynomolgus monkeys (Macaca fascicularis) were trained in a task that assessed their ability to associate visual stimuli with food reward. Acquisition of stimulus-reward associations was measured under 2 conditions, a 2-stimuli acquisition condition and a 1-stimulus acquisition condition. On each trial in the 2-stimuli condition, the positive (correct) and negative (incorrect) stimuli were presented side by side and the animal chose one by touching it; if the choice was correct, a food reward was dispensed. On each trial in the 1-stimulus condition, either the positive or the negative stimulus was presented alone; if the stimulus was the positive, it was followed by reward delivery, regardless of the animal's response to it, and if it was the negative, it was not followed by reward delivery. Thus, reward delivery was contingent upon the animal's response to the stimuli in the 2-stimuli condition but not in the 1-stimulus condition. The effect of acquisition trials under these 2 conditions was measured, in both conditions, by the animal's subsequent choice when presented with the 2 stimuli side by side. Following preoperative training in this task, the animals were first subjected to unilateral ablation of the inferotemporal cortex. This operation had little effect on the animals' learning ability. Then, the amygdala was ablated in the hemisphere contralateral to that in which the unilateral inferotemporal ablation had been carried out. This combination of crossed unilateral lesions of the amygdala and of the inferotemporal cortex, which disconnects the amygdala from the output of visual association cortex, produced a profound impairment in stimulus-reward-associative learning.(ABSTRACT TRUNCATED AT 250 WORDS)

Acoustic Stimulation↗
PubMed1987

Amygdalectomy and disconnection in visual learning for auditory secondary reinforcement by monkeys.

Nine monkeys in 3 groups took part in an experiment on visual discrimination learning set in an automatic apparatus. Each new visual discrimination problem was solved using auditory secondary reinforcers. Primary food reinforcement was delivered only after a new problem had been solved to a criterion, and the problem was then replaced by a new one; thus, within-problem learning relied purely on secondary and not on primary reinforcement, but the secondary reinforcers were associated with primary reinforcement. Bilateral amygdalectomy severely retarded within-problem learning. Disconnection of the amygdala from auditory input, by crossed unilateral lesions of amygdala and of auditory cortex combined with forebrain commissurotomy, had a similar effect to that of bilateral amygdalectomy. Disconnection of the amygdala from visual association cortex left learning unimpaired. Thus, for normal performance in this task, interaction of the amygdala with the sensory modality of the secondary reinforcer was essential, but interaction of the amygdala with the sensory modality of the discriminative stimuli was not necessary. It was concluded that the amygdala is involved in associating stimuli with the primary reinforcing attributes of food reward, and not with its other attributes.

Amygdala↗
PubMed1987

Monkey hippocampus and learning about spatially directed movements.

Monkeys were given a series of problems to solve in which they had to learn whether to approach a given visual stimulus and make repeated contact with it or to withdraw from the stimulus and avoid making contact with it. The reward for the correct response in either case (approach or withdrawal) was food, which was always delivered in the same spatial location. This task requires the animal to learn in what spatial direction to move in relation to the visual stimuli, but it cannot be solved by learning the spatial relationships among stimuli in the environment. Transection of the fornix severely impaired the monkeys' learning ability in this task; bilateral ablation of the sulcus principalis did not. This result shows that the hippocampus is concerned with learning about spatially directed movement, rather than with the acquisition of maplike knowledge about the spatial relationships of stimuli in the environment.

Animals↗
PubMed1985

Hippocampus: memory, habit and voluntary movement.

A general method for studying monkeys' memories is to teach the animals memory-dependent performance rules: for example, to choose, out of two visual stimuli, the one that flashed last time the animal saw it. One may thus assess the animal's memory for any arbitrarily chosen event such as flashing even if the event itself has no intrinsic importance for the animal. The method also allows assessment of an animal's memory of the animal's own previous behaviour. The use of these methods has revealed a simple generalization about the function of the hippocampus in memory: hippocampal lesions impair memory of the voluntary movement that a stimulus previously elicited, but leave intact memory for relations between environmental events other than voluntary movements. The impairment in memory for voluntary movements produces deficits in exploration and in habit formation.

Animals↗
PubMed1980

Recency effects and lesion effects in delayed non-matching to randomly baited samples by monkeys.

Monkeys' memory for 3-dimensional junk objects was tested in a task which required them to discriminate objects which had recently been presented in an acquisition list from new objects which had not. The accuracy of this discrimination was shown to depend on the recency of presentation of the old object. The discrimination was not significantly affected by lesions of either the foveal pre-striate cortex, the fundus of the superior temporal sulcus, or the anterior inferior temporal area. A substantial impairment was caused by transection of the fornix.

Animals↗