Hisae Gemba

Potential related to no-go reaction of go/no-go hand movement task with color discrimination in human

Twenty-three human subjects were asked to perform a go/no-go reaction-time hand movement task with discrimination between different color light signals, and potentials related to the discrimination task were recorded with plate electrodes placed on the scalp and analyzed by averaging procedures. A negative potential was found to be recorded specifically to no-go trials in the frontal-parietal part of 21 subjects out of 23 tested. In referring to our recent experiments with monkeys, it is suggested that the potential is related to the judgement not to move and/or the suppression of motor execution.

Potential related to no-go reaction in go/no-go hand movement with discrimination between tone stimuli of different frequencies in the monkey

Monkeys were trained for go/no-go reaction-time hand movement with discrimination between tone stimuli of different frequencies, and field potentials related to the discriminative movement were recorded with electrodes implanted in various cortical areas and analysed by averaging procedure. In the cortex of the dorsal bank of the principal sulcus, surface-negative, depth-positive (s-N, d-P) potentials were recorded specifically on the no-go trial. The same monkey was also examined for go/no-go reaction-time hand movement with color discrimination. In the same monkey, the potentials related to the no-go reaction on the auditory stimulus were recorded in the rostral part of the dorsal bank of the principal sulcus, whereas the s-N, d-P potentials on the no-go visual stimulus were observed in the caudal part of the same bank. It is suggested that the dorsal bank of the principal sulcus is essentially related to the integrative functions such as judgement not to move and suppression of motor execution, and that different loci in this cortical area are respectively active for the functions of different sensory modalities.

Compensatory motor function of the somatosensory cortex for the motor cortex temporarily impaired by cooling in the monkey.

SummaryThe motor cortex was temporarily impaired by local cooling during repeated execution of visually initiated hand movements in monkeys. The effects of cooling were examined by recording premovement cortical field potentials in the forelimb motor and somatosensory cortices and by measuring reaction time and force exerted by the movement. The cortex was cooled by perfusing cold water (about 1° C) through a metal chamber placed on the cortical epidural surface. Cooling of the forelimb motor area lowered temperature of the cortex under the chamber to 20–29° C within 4–5 min. Recording electrodes for cortical field potentials were implanted chronically on the surface and at 2.5–3.0 mm depth of various cortical areas including that being cooled. Spread of cooling to surrounding cortical areas was prevented by placing chambers perfused with warm water (38–39° C) on the areas.Cooling of the forelimb motor area greatly reduced its premovement cortical field potentials, followed by prolonged reaction times of weakened contralateral wrist muscles. Simultaneous recording from the primary somatosensory cortex revealed an enhancement of its premovement field potentials. All changes were completely reversible by rewarming of the motor cortex. Concomitant cooling of the motor and somatosensory cortices entirely paralysed the contralateral wrist muscles. These results suggest that the motor function of the somatosensory cortex becomes predominant and compensates for dysfunction of the motor cortex when it is temporarily impaired.

Cortical field potentials associated with hand movements triggered by warning and imperative stimuli in the monkey

Monkeys were trained to move the hand in response to imperative visual stimulus (IS) given 1 s after warning visual stimulus (WS). With implanted electrodes in the cortices, surface-negative (s-N), depth-positive (d-P) sustained potentials between WS and IS were recorded in the prefrontal, premotor and supplementary motor areas in both hemispheres, and gradually increasing s-N, d-P potentials were seen in the forelimb areas of motor and somatosensory cortices contralateral to the hand. It is suggested that the sustained and gradually increasing potentials are related respectively to cortical activities associated with expectation and anticipation of the IS, and to those with a preparatory process for the movement. The latter appeared to be similar to the case of self-paced movements. These potentials may correspond respectively to the early and late components of CNV in the human.

Compensatory motor function of the somatosensory cortex for dysfunction of the motor cortex following cerebellar hemispherectomy in the monkey

SummaryElectrical activities of the motor and somatosensory cortices preceding visually-initiated hand movements were recorded with electrodes chronically implanted on the surface and at 2.5–3.0 mm depth in the cortex of monkeys, and changes in field potentials in these cortices after cerebellar hemispherectomy were observed for many weeks. As previously reported, a unilateral cerebellar hemispherectomy including the lateral and interpositus nuclei eliminates the cerebellar-mediated superficial thalamo-cortical (T-C) responses recorded in the forelimb motor cortex contralateral to the hemispherectomy. These T-C responses normally precede the hand movement, and the operation results in the delay of movement initiation. The electrodes in the forelimb area of the contralateral primary somatosensory cortex showed an enhancement of superficial T-C responses of the somatosensory cortex for 30–40 days after the operation. The enhanced potentials preceded the delayed movement as do the cerebellar-mediated superficial T-C responses of the motor cortex in normal situations. Local cooling of the somatosensory cortex following the cerebellar hemispherectomy disturbed the reaction time movement for a few weeks after the operation. This effect was rarely encountered in normal monkeys. The present study suggests the compensatory motor function of the somatosensory cortex for the dysfunction of the motor cortex in early weeks after cerebellar hemispherectomy.

Cortical field potential associated with hand movement on warning-imperative visual stimulus and cerebellum in the monkey

Latent time of the hand movement in response to a visual stimulus was found to be very short when a monkey was enough trained with a visual imperative stimulus preceded by a visual warning stimulus at a fixed time interval. Cerebellar hemispherectomy scarcely prolonged the reaction time of the warning-imperative, visually initiated (W-VI) movement in contrast to its marked delaying action upon the simple visually initiated reaction-time (S-VI) movement. Between the warning and imperative stimuli, sustained surface-negative, depth-positive field potentials were recorded in various areas of the prefrontal and premotor cortices and the supplementary motor area of both cerebral hemispheres, besides gradually increasing surface-negative, depth-positive deflections in the motor and somatosensory cortices contralateral to the moving hand. These observations suggest that the sustained activities in the prefrontal and premotor cortices elicited by the warning stimulus overcome deficiency of the cerebellar function for performing fast and stable timing movements.

Cortical field potentials associated with audio-initiated hand movements in the monkey

SummaryMonkeys were trained to respond to auditory stimulus by lifting a lever (audio-initiated hand movement), and field potentials were recorded. from various cortical areas with electrodes implanted on the surface and at a depth of 2.0–3.0mm, depending on the area. Tones of 500, 1000 and 2000 Hz were given to the monkey for about 500 or 10 ms, as auditory stimuli. In association with the movement, potentials of different configurations were recorded respectively in the primary auditory, auditory association, prefrontal, premotor, motor and somatosensory cortices. Initial surface-positive (s-P), depthnegative (d-N) potentials appeared in the primary auditory and auditory association cortices about 20 ms after the onset of the auditory stimulus, and they were often followed by s-N, d-P potentials. In the forelimb area of the motor cortex contralateral to the moving hand, s-N, d-P potentials appeared at a latency of about 100 ms. Following cerebellar hemispherectomy ipsilateral to the moving hand, the s-N, d-P potentials in the forelimb motor cortex were eliminated and reaction times prolonged. The same monkeys were also trained to perform a visuoinitiated movement, and results were compared with each other. Primary sensory and sensory association areas activated during such movements were certainly different, and the prefrontal association cortex appeared to participate much less predominantly in the audio- than in the visuo-initiated movement. Reaction times were generally longer and more variable for the audio- than for the visuo-initiated movement. Nevertheless the cerebello-thalamomotor cortical projection was found to be recruited in the same manner prior to both movements.

No-Go Potential in the Prefrontal Cortex of Monkeys

Various parts of the cerebral cortex reveal different kinds of electrical activities upon execution of simple reaction-time hand movements in response to visual stimuli in the monkey (Fig. 1) (Gemba et al. 1981; Sasaki and Gemba 1982). In the prefrontal cortex, predominant field potentials at a relatively short latency after the onset of visual stimulus were found in the ventral part of the arcuate area and its continuation ventral to the caudal part of the principal sulcus (“prearcuate area”) of both hemispheres (Fig. 1 A, IPSILATERAL A, diagrams to the right) (see Sasaki and Gemba 1982). A gradual increase in the potential in the prearcuate area during learning processes of the simple reaction-time movement was assumed to be correlated with the recognition learning of the movement, i.e., association of the visual stimulus with the hand movement (Sasaki and Gemba 1982). In the well trained monkey, the prearcuate area was found, with a local cooling method, to be one of the important cortical areas which send the motor command of the visually initiated movement to the motor cortex through the neocerebellum and thalamus (Sasaki and Gemba 1987).