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H Gemba

Publications and source records attributed to H Gemba.

At least 55 records · Page 3Linked to original sources
PubMed1983

Learning of fast and stable hand movement and cerebro-cerebellar interactions in the monkey.

Monkeys were trained to lift a lever by wrist extension in response to a light stimulus and changes of premovement cortical field potentials were observed during the training period with electrodes which had been chronically implanted in various cortical areas. The purpose of the study was to follow changes in potentials mediated by cerebro-cerebellar neuronal circuits as fast and stable hand movements were attained during later stages of motor learning. As compared to initial stages of an operantly conditioned movement in response to the light stimulus, further training shortened reaction times gradually over several weeks, and this was associated with gradual increases of premovement superficial thalamo-cortical (T-C) responses in the contralateral forelimb motor area. Since the T-C responses are known to depend at least in part on impulses from the neocerebellum, it is suggested that the neocerebellum--superficial T-C projection--motor cortex system is gradually recruited during motor learning and that this in turn contributes to fast and stable movements.

Animals↗
PubMed1982

Cortical field potentials preceding visually initiated hand movements and cerebellar actions in the monkey.

Cortical field potentials preceding hand movements initiated by a visual stimulus were recorded with chronically implanted electrodes in premotor, motor and somatosensory cortices of monkeys, and the influences of cerebellar hemispherectomy on cortical potentials as well as reaction time of movements were examined. As reported previously, early surface-positive, depth-negative (2.5-3 mm depth from the cortical surface) premovement potentials emerged at about 40 ms latency after onset of the light stimulus bilaterally in premotor and forelimb motor areas. Early potentials in the forelimb motor area contralateral to the moving hand were followed at about 120 ms latency by surface-negative, depth-positive late premovement potentials which are considered to be mainly composed of superficial thalamo-cortical (T-C) responses. Unilateral hemispherectomy of the cerebellum contralateral to the motor area immediately eliminated the surface-negative, depth-positive potentials. Reaction time from onset of the light stimulus to the hand movement was prolonged by 90-250 ms after cerebellar hemispherectomy. If the dentate and interpositus nuclei were also lesioned, disappearance of the late potentials and delay of the movement continued for many months. However, if the interpositus was spared, there was earlier recovery of reaction time with simultaneous reappearance of the late premovement potentials in the motor cortex. The conclusion is drawn that the cerebellar hemisphere (neocerebellum) activates the motor cortex via superficial T-C projections and participates directly in the initiation of reaction movements in response to an external stimulus.

Animals↗
PubMed1982

Development and change of cortical field potentials during learning processes of visually initiated hand movements in the monkey.

Field potentials on the surface and at 2.5-3.0 mm depth in the cerebral cortex were recorded in various areas with chronically implanted electrodes and the potentials which preceded hand movements in response to a light stimulus were observed during the process of learning the skilled conditioned movement. A naive monkey had to lift a lever by wrist extension within duration of the light stimulus lasting for 900, 700 or 510 ms depending on the stage of the learning process. In addition to some responses in the striate gyrus, significant short-latency responses to the light stimulus appeared bilaterally in certain areas of the prefrontal and prestriate cortices at an early stage of learning in which the monkey still lifted the lever randomly, and they became gradually larger as the monkey was trained further. Short-latency responses were also often noted in the bilateral premotor cortices during an early stage of learning. When the monkey started to respond to the stimulus by the appropriate movement, early surface-positive (s-P), depth-negative (d-N) premovement potentials appeared in the forelimb motor cortex, and the responses in the premotor cortex increased in size. As the movement became faster and more skillful, late s-N, d-P premovement potentials, that are known to be mediated by the neocerebellum and superficial thalamo-cortical projections, emerged after the early s-P, d-N potentials and became more marked, larger and steeper in the forelimb motor cortex contralateral to the moving hand. All the premovement potentials in the different cortical areas thus developed into steady and constant states and remained so for many months thus maintaining their established patterns. Such successive appearances of premovement field potentials in various cortical areas were related to learning processes of the movement and the implication of these findings was discussed.

Animals↗
PubMed1981

Changes of premovement field potentials in the cerebral cortex during learning processes of visually initiated hand movements in the monkey.

Field potentials on the surface and in the depth (2.5-3.0) mm from the surface) of several areas of the cerebral cortex were recorded with chronically implanted electrodes and with electronic averaging method, and changes of the potentials preceding visually initiated (reaction) hand movements were observed successively in the time course of leaning the movement in monkeys. Significant potentials in response to the light stimulus were found first in the frontal and occipital association cortices (area 8-10 and 19), and then in the premotor cortex (area 6) on bilateral sides. In the bilateral forelimb motor cortex (area 4), the early surface positive-depth negative premovement potentials became marked after the occurrence of the significant potentials in the frontal and occipital association cortices, and the later surface negative-depth positive premovement potentials mediated by the neocerebellum and the superficial thalamocortical projections emerged later in the forelimb motor cortex contralateral to the moving hand as the monkey became fast and skilled in the movement. Learning processes of the reaction movement were related to such changes of the premovement potentials in the cerebral cortical areas.

Animals↗
PubMed1981

Distribution of slow cortical potentials preceding self-paced hand and hindlimb movements in the premotor and motor areas of monkeys.

Surface negative-depth positive, slowly increasing potentials prior to self-paced hand and hindlimb movements were recorded in the dorsal aspect of the motor and premotor cortices with chronically implanted electrodes. It was shown that the potentials were recorded in the contralateral forelimb motor area prior to hand movements but were hardly seen in the hindlimb motor area. On hindlimb movements, the contralateral hindlimb motor area showed the premovement potentials, whereas the forelimb motor area revealed little or no premovement potentials. The contralateral premotor cortex was shown to induce the premovement potentials in its wider areas and participate in both of hand and hindlimb movements in a similar fashion, with predominances in its dorsolateral portion for hand movements and in its dorsomedial portion for hindlimb movements respectively. In the hemisphere ipsilateral to the moving hand, the relatively large premovement slow potentials emerged frequently also in the premotor cortex, whereas only the small potential was obtained from the forelimb motor area. These results suggest that the premotor cortex (area 6) participates in the more general and associative organization of motor function than the motor cortex (area 4) which represents the specialized role in the motor performance.

Action Potentials↗
PubMed1981

Cortical field potentials preceding self-paced and visually initiated hand movements in one and the same monkey and influences of cerebellar hemispherectomy upon the potentials.

Field potentials in the premotor and forelimb motor cortices preceding hand movements were recorded with chronically implanted electrodes in the cortices. They were different between the same hand movements initiated at self-pace ('voluntary') and by visual stimulus (in reaction) in the same monkey. Ablation of the cerebellar hemisphere contralateral to the motor cortex suppressed both slowly increasing and relatively steep surface negative-depth (2.5-3.0 mm) positive potentials in the motor cortex prior respectively to self-paced and visually initiated movements. The results inferred the different central preparatory mechanisms (programs) for self-paced and reaction movements in the same individual, and revealed the direct neocerebellar participation in initiation of both self paced and reaction movements by activating the motor cortex.

Animals↗
PubMed1981

Influences of cerebellar hemispherectomy upon cortical potentials preceding visually initiated hand movements in the monkey.

With chronically implanted electrodes, surface and depth potentials of the premotor and motor cortices were recorded on hand movements in response to a visual stimulus in monkeys, and influences of cerebellar hemispherectomy were examined upon visually initiated premovement cortical potentials. Early, surface positive--depth negative premovement potentials emerged in the cortices on both sides, and following surface negative--depth positive premovement potentials appeared in the motor cortex contralateral to the moving hand. Cerebellar hemispherectomy contralateral to the motor cortex eliminated the following potentials. This suggests the participation of the neocerebellum in preparing the motor cortex for visually initiated movements.

Animals↗
PubMed1981

Cortical field potentials preceding visually initiated hand movements in the monkey.

With electrodes implanted chronically on the surface and in the depth of the cortex, field potentials were led from the premotor cortex and forelimb areas of the motor and somatosensory cortices of monkeys performing visually initiated hand movements, and then averaged. It was found that the visually initiated movement was preceded by early (latency about 40 ms after the visual stimulus), surface positive, depth negative potentials in the premotor and forelimb motor cortices on both sides. Later on (at about 120 ms latency), surface negative, depth positive potentials emerged prior to the movement in the motor cortex contralateral to the moving hand. The early responses were interpreted as being induced via deep thalamo-cortical and/or corticocortical projections, while the later responses were via superficial thalamo-cortical projections, according to laminar field potential analyses of cortical evoked potentials made in our previous acute experiments. These potentials recorded in the respective cortices prior to self-paced hand movements: monkeys performing self-paced hand movements showed slowly increasing, surface negative, depth positive premovement potentials in the premotor cortex and the forelimb motor and somatosensory areas contralateral to the moving hand. It was concluded that the central nervous mechanism preparing the cerebral cortex for visually initiated movements is considerably different from that for self-paced movements, both of which consist of the same wrist extension in lifting a lever.

Animals↗
PubMed1980

Premovement slow cortical potentials and required muscle force in self-paced hand movements in the monkey.

Surface negative--deep positive, slowly increasing potentials prior to self-paced hand movements were recorded in the contralateral premotor, motor and somatosensory cortices, with chronically implanted electrodes. Such premovement slow potentials in the 3 cortical areas changed their magnitudes with the required muscle force in the hand movement, and the potentials in the different cortices appeared to differ slightly in the manner of change. These results may suggest that the EPSPs in the superficial parts of apical dendrites of cortical pyramidal neurons principally via certain thalamo-cortical projections are induced prior to movements in the cortices so as to adjust the required force on anticipation, and that the premotor, motor and somatosensory cortices play some different functional roles in preparatory processes for the movement performance.

Animals↗
PubMed1980

Distribution of premovement slow cortical potentials associated with self-paced hand movements in monkeys.

With electrodes chronically implanted on the surface and in the depth of the cerebral cortex, field potentials were led from various cortical areas of the bilateral hemispheres of monkeys performing self-paced hand movements. In the hemisphere contralateral to the moving hand, surface negative-depth positive, slowly increasing premovement potentials were recorded in wider portions of the premotor cortex and in the forelimb areas of the motor and somatosensory cortices. In the ipsilateral hemisphere, the potentials of relatively large amplitudes were often obtained in the premotor cortex, whereas either small or no premovement potentials were recorded in the motor and somatosensory cortices.

Animals↗
PubMed1979

Projection of the cerebellar dentate nucleus onto the frontal association cortex in monkeys.

Stimulation of the cerebellar dentate nucleus in monkeys elicited responses in the frontal association cortex (area 9) on the contralateral side to the stimulation, in addition to those in the motor (area 4) and premotor (area 6) cortices which were reported previously. The responses in the frontal association cortex were characterized by surface positive-deep negative field potentials in the cortex. They contrasted with surface negative-deep positive potentials in the motor and premotor cortices on the same dentate nucleus stimulation. In the rostral part of the premotor cortex (area 6) on the border of area 9, both types of responses were induced and admixed. The relay nucleus of the thalamus was suggested for the dentate-induced responses in the frontal association cortex.

Animals↗
PubMed1979

Influences of cerebellar hemispherectomy on slow potentials in the motor cortex preceding self-paced hand movements in the monkey.

With chronically implanted electrodes, surface negative and deep positive, slowly increasing potentials were recorded in the forelimb area of the motor cortex prior to self-paced movements of the contralateral hand in monkeys. The slow premovement potentials were markedly reduced in size after ablation of the cerebellar hemisphere on the contralateral side to the motor cortex under recording. It was suggested that the cerebellar hemisphere (neocerebellum) participates in preparing the activity of the motor cortex prior to voluntary movements.

Animals↗
PubMed1979

Slow potentials preceding self-paced hand movements in the parietal cortex of monkeys.

In our previous paper, surface negative-deep positive slow potentials were reported to appear prior to self-paced hand movements in the premotor and the forelimb motor cortices of unanesthetized, freely moving monkeys, as recorded with the elctrodes implanted chronically in the cortices. The present study revealed that similar slow potentials were recorded also in the somatosensory cortex in most cases, but infrequently and unmarkedly in area 7, never in area 19.

Animals↗