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Prism adaptation and other tasks involving spatial abilities in patients with Parkinson's disease, patients with frontal lobe lesions and patients with unilateral temporal lobectomies.
Patients in the early stages of Parkinson's disease were compared with patients who had sustained damage specific to either the frontal or temporal lobes and normal controls on a delayed alternation task, a test of the left right orientation and a prism adaptation task. On the former two tasks age accounted for more of the variability in performance than did site of brain lesion. However, patients with frontal lobe, right temporal lobe or basal ganglia damage were significantly impaired on the adaptation task. The results are discussed with regard to "switching", "sequencing" and "internal guidance" of movement hypotheses.
Sequence ability in parkinsonians, patients with frontal lobe lesions and patients who have undergone unilateral temporal lobectomies.
Patients in the early stages of Parkinson's disease were compared with patients who had sustained damage specific to either the frontal or temporal lobes and normal controls on a number of sequencing tests. These tests involved the reproduction of sequences of hand gestures, sequences tapped out on blocks, and sequences of digits. Only the groups with frontal lobe lesions or right temporal lobectomies were impaired on any of these tasks, though no group was impaired on all of the sequencing tasks.
Premotor cortex and the retrieval of movement.
It is argued that the premotor cortex plays a crucial role in the retrieval of movement. Monkeys with bilateral lesions in premotor cortex were found to be impaired at selecting between two movements on the basis of visual cues. This was true whether the visual cue was present at the time of response or was no longer visible. Yet other monkeys with bilateral lesions in dorsal premotor cortex had little difficulty in remembering a movement if they had just been forced to make it a few seconds earlier. It is suggested that the premotor cortex is involved in the process of translation from a visual or auditory cue to an associated movement.
Motor learning in monkeys (Macaca fascicularis) with lesions in motor thalamus.
The study examines the nature of the influence that the basal ganglia exert on frontal cortex via the motor nuclei of the thalamus. Twelve monkeys were trained to pull a handle given one colour cue and to turn it given another. Bilateral lesions were then placed in the ventral thalamus. Four monkeys with large anterior lesions including the VA nucleus and the anterior part of VLo were severely impaired at relearning the task. Monkeys with small lesions in VAmc or with lesions centred on VLo were not impaired. The analysis of the histology suggests that the impairment in the four monkeys did not result from involvement of the cerebellar relay through nucleus X. It is argued that the animals are not impaired because of faulty execution. This suggests that the basal ganglia have an influence on motor learning.
The performance on learning tasks of patients in the early stages of Parkinson's disease.
It is known that in animals learning is disrupted by caudate lesions; but there has been no agreement about whether pathology in the basal ganglia causes a similar impairment in man. Nineteen patients in the early stages of Parkinson's disease were tested on two associative learning tasks and on the Wisconsin Card Sorting Task; and their performance was compared with that of patients with frontal or temporal lobe lesions. On the two associative learning tasks there was no overall difference between the Parkinsonian group and the controls. However, a minority of the Parkinsonian patients performed very poorly on these tasks; and it was noted that these tended to be the older patients.
Premotor cortex and preparation for movement.
Many cells in premotor cortex change their activity while a monkey waits before responding. In the present experiment lesions were placed in premotor cortex in order to investigate the information carried by this neuronal activity. The monkeys were trained to make one of two movements depending on the colour of a cue. There were two conditions: in one they could respond when the cue was presented, in the other they had to wait three seconds before responding. The monkeys were then retested after the bilateral removal of premotor cortex. Animals with premotor lesions performed very poorly under both conditions. It is concluded that premotor cortex is concerned with retrieving the response that is appropriate given a particular cue.
Two cortical systems for directing movement.
It is argued that the cortical premotor areas are concerned with the conditions for action. Actions are based both on facts about the outside world and about the actions of the animal itself. Observations on monkeys (Macaca fascicularis, Macaca mulatta) suggest that the arcuate premotor area directs actions on the basis of visual cues about the outside environment and that the supplementary motor area directs actions on the basis of proprioceptive cues concerning the animal's own actions.
Reorganization in the human brain as illustrated by the thalamus.
A comparison is made between the relative size of the various thalamic nuclei in man and other primates. Using data for non-human primates predictions are made as to the expected size of the nuclei for the human brain. Of the nuclear groupings five are of the size predicted but three are not. The lateral geniculate is proportionately smaller than predicted, but it is argued that this need not imply a radical change.
Prefrontal cortex and the sequencing of movement in monkeys (Macaca mulatta).
There have been suggestions that the prefrontal cortex may play a role in the regulation of higher-order sequences of behaviour. In this experiment monkeys were taught a sequence of three movements. After removal of either sulcus principalis or the superior prefrontal convexity monkeys were able to perform the sequence normally. After removal of arcuate cortex (areas 8 and 6) monkeys were slow to learn the task; but it is argued that their impairment may not be one of sequencing per se.
Stereotaxic surgery under X-ray guidance in the rhesus monkey, with special reference to the amygdala.
The anterior/posterior (AP) positions of three subcortical regions; the amygdala, supra-optic nucleus of the hypothalamus and mammillary bodies, were estimated with respect to the skull in 35 rhesus monkeys (Macaca mulatta). The distances from the external auditory meatus, from which stereotaxic coordinates are typically derived, to these subcortical nuclei were found to be highly variable. In contrast the posterior tip of the sphenoid bone, which was visualized on lateral radiographs, provided a landmark at a remarkably constant AP distance from these nuclei. This landmark was used to guide a series of a amygdaloid lesions and injections. The accuracy of these operations strongly suggested that the posterior tip of the sphenoid bone could be used to predict not only the AP but also the height of the amygdala. It is proposed that this radiographic technique could be applied to other hypothalamic and basal forebrain regions.