Movement-related cortical potentials associated with voluntary relaxation of foot muscles.

OBJECTIVE: In our previous study of movement-related cortical potential (MRCP) in association with the voluntary relaxation of the hand muscle, Bereitschaftspotential (BP) was maximal at the vertex and symmetrically distributed, and Negative Slope (NS') was maximal over the contralateral central region. In order to clarify the generator sources of MRCP with voluntary muscle relaxation, we recorded MRCP in association with voluntary relaxation of the foot. METHODS: MRCP in association with plantar flexion of the foot caused by voluntary relaxation of the tibialis anterior muscle was recorded in 10 normal subjects. RESULTS: The BP started at about 1.7 s before the onset of the muscle relaxation, followed by NS' starting at about 650 ms before it. Both were maximal at the vertex and symmetrically distributed. There was no additional EEG activity in the lateral frontal areas, which are presumably located over the primary negative motor areas (PNMA). CONCLUSIONS: It is concluded that the voluntary muscle relaxation, similarly to the voluntary muscle contraction, involves the cortical preparatory activity at least in the primary motor area (M1) and probably the supplementary motor areas (SMAs). There is no evidence to suggest that the PNMA is also active prior to the voluntary muscle relaxation.     

Expectancy-related cerebral potentials associated with voluntary time estimation and omitted stimulus

Expectancy-related and nonexpectancy-related cerebral potentials associated with stimuli and omitted stimuli were recorded in 7 normal subjects. The stimuli were constantly delivered to the right median nerve and the interstimulus interval was set at 7 seconds. When the subject counted to estimate the interstimulus interval correctly, a slow negative deflection appeared about one second prior to both the stimuli and the omitted stimuli. In the case of the omitted stimulus, this expectancy-related negative potential (ENP) returned to the base line after several hundred msec. When the stimuli were delivered, the amplitude of the P300 was much higher when the subject was paying attention to the stimuli than when he was not. The scalp distribution of the ENP was rather anterior to the P300. No ENP appeared when the subject was not paying attention to the stimuli or the omitted stimuli, or when the stimuli were delivered at a random rate.     

Effect of voluntary self-paced movements upon auditory and somatosensory evoked potentials in man.

The effect of voluntary self-paced movements upon auditory (AEPs) and somatosensory (SEPs) evoked potentials has been investigated according to the temporal relationship between movement and delivery of test stimuli. EPs were recorded in 7 subjects and averaged in 10 successive epochs extending from 880 msec before to 2500 msec after movement. AEPs were attenuated in all epochs. The decrease was greatest in the 220 msec epoch just following movement and involved components N85 and P170. SEPs were attenuated similarly to AEPs when movements were performed by the hand contralateral to somatosensory stimulation. Of the 5 SEP components, only P40 failed to reflect the attenuation, while P95 showed the greatest amplitude decrease. When stimulation was ipsilateral, SEP amplitude was attenuated only when close to the movement. N65 and P95 decreased while N130 increased. In all subjects the results were consistent for treatments of AEP and SEP (with contralateral movements), whereas large inter-individual differences were observed for the SEP with ipsilateral movements.     

Analysis of slow cortical potentials preceding self-paced hand movements in the monkey.

Cortical potentials related to the self-paced “voluntary” hand movement were recorded in unanesthetized, freely moving monkeys with the electrodes implanted chronically on the surface and in the depth of the cortex, and analyzed with the method of electronic averaging. Prior to the movement, surface negative — deep positive slow potential changes appeared in the motor and premotor cortices contralateral to the moving hand. The potential changes started about 1 s before the hand movement and increased gradually to about 100 ms before the movement. The contours of the potential changes preceding the movement were remarkably constant in daily recording for several weeks. Based on the laminar field potential analyses of cortical evoked potentials made in previous acute experiments, the slow potential was interpreted to be due to the currents of slowly increasing EPSPs that were generated in superficial parts of the cortical pyramidal neurons via certain thalamocortical projections. The EPSPs would activate the neurons in the motor and premotor cortices and contribute to the initiation of voluntary movement.     

Cortical activities associated with voluntary movements and involuntary movements

Recent advance in non-invasive techniques including electrophysiology and functional neuroimaging has enabled investigation of control mechanism of voluntary movements and pathophysiology of involuntary movements in human. Epicortical recording with subdural electrodes in epilepsy patients complemented the findings obtained by the non-invasive techniques. Before self-initiated simple movement, activation occurs first in the pre-supplementary motor area (pre-SMA) and SMA proper bilaterally with some somatotopic organisation, and the lateral premotor area (PMA) and primary motor cortex (M1) mainly contralateral to the movement with precise somatotopic organisation. Functional connectivity among cortical areas has been disclosed by cortico-cortical coherence, cortico-cortical evoked potential, and functional MRI. Cortical activities associated with involuntary movements have been studied by jerk-locked back averaging and cortico-muscular coherence. Application of transcranial magnetic stimulation helped clarifying the state of excitability and inhibition in M1. The sensorimotor cortex (S1-M1) was shown to play an important role in generation of cortical myoclonus, essential tremor, Parkinson tremor and focal dystonia. Cortical myoclonus is actively driven by S1-M1 while essential tremor and Parkinson tremor are mediated by S1-M1. 'Negative motor areas' at PMA and pre-SMA and 'inhibitory motor areas' at peri-rolandic cortex might be involved in the control of voluntary movement and generation of negative involuntary movements, respectively.     

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.     

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.     

Premovement slow cortical potentials on self-paced hand movements and thalamocortical and corticocortical responses in the monkey

Chronically implanted electrodes on the surface and in the depth of the motor cortex in the monkey could record slowly increasing, surface negative-depth positive potentials that precede self-paced hand movements. Such premovement slow cortical potentials were interpreted to be composed mainly of currents due to excitatory postsynaptic potentials in superficial parts of the apical dendrites of pyramidal neurons through certain thalamocortical projections. To test the interpretation, the same electrodes were utilized to record cerebellothalamocortical responses and corticocortical responses evoked by electrical stimulation of the cerebellar nucleus and of the cerebral cortex. These results were compared with the laminar field potentials of cerebellothalamocortical and corticocortical responses recorded with glass microelectrodes in acute experiments with monkeys. The present study revealed a similarity of the cortical depth profile of premovement slow cortical potentials to that of the dentatothalamocortical responses, and supported the interpretation.     

Cortical potentials following voluntary and passive finger movements

In order to clarify the time relationship and functional significance of post-motion components of the movement-related cortical potential, averaged cortical potentials associated with voluntary and passive movements were compared mainly with respect to their scalp topography. Fourteen channels of scalp EEG, together with EOG and EMG, were simultaneously recorded in 7 healthy adult subjects while the subject was either repeating a self-paced brisk extension of a middle finger or while the experimenter was extending the middle finger by pulling up a string attached to the finger. Potentials associated with the movement were averaged opisthochronically in relation to a trigger actuated by the finger interrupting a beam of light. Seven peaks were identified in the passive movement-evoked potential. A sharp negative peak occurred over the contralateral precentral region 16 msec after the photometer trigger (N15). Another negative component (N70) formed a composite of double-peaked negativity with N15 and was seen over the frontal region with a contralateral predominance. A positive peak (P65) was recorded over the contralateral parietal region with a similar latency to N70. This N70/P65 complex has some marked similarities in terms of wave form and spatial relationship with the N + 50/P + 90 complex recorded with voluntary movement of the same finger. It is postulated that these components may be the projected potential fields from a dipole source within the central sulcus and may represent a kinesthetic feedback from the muscle afferents.     

Distribution of potentials preceding visually initiated and self-paced hand movements in various cortical areas of the monkey

A monkey was trained to lift a lever by its hand in response to a light stimulus or at self-pace; field potentials preceding, respectively, visually initiated and self-paced movements were recorded in various areas on the dorso-lateral and mesial surface of the cerebral hemisphere, with electrodes implanted chronically on the surface and at 2.5-3.0 mm depth of respective cortical areas. Slowly rising, surface-negative, depth-positive (s-N, d-P) potentials were obtained prior to the self-paced movement in the bilateral premotor cortex, and in the contralateral forelimb motor, somatosensory and mesial premotor areas, resembling 'readiness potentials'. Potentials preceding the visually initiated movement occurred in more cortical areas than the self-paced movement, with characteristic potential features to respective areas. In bilateral prefrontal and prestriate cortices, early s-P, d-N and following s-N, d-P potentials were obtained. Only early s-P, d-N potentials occurred bilaterally in the premotor cortex. In the contralateral forelimb motor area, early s-P, d-N and late s-N, d-P premovement potentials were observed. In the mesial premotor area, s-P, d-N and following s-N, d-P potentials were recorded at a little longer latency and with smaller amplitude than in the motor cortex.     

EMG analysis of stereotyped voluntary movements in man.

EMG activity was recorded in biceps and triceps while subjects voluntarily flexed their elbows during a visual matching task. With fast flexion, the initial EMG was characterized by a triphasic pattern with a burst of activity first in biceps, then in triceps with a silent period in biceps, and finally in biceps again; these components were analysed quantitatively. Smooth flexion was characterized by continuous activity in biceps. Inhibition of tonic activity of triceps in relation to a fast flexion occurred in the 50 ms before the initiation of biceps activity. A patients with a severe pansensory neuropathy performed normally on these tasks. Physiological mechanisms underlying these patterns are analysed; an important conclusion is that the triphasic activity with fast flexion is 'centrally programmed'.     

Different cortical potentials preceding self-paced and visually initiated hand movements and their reciprocal transition in the same monkey

With chronically implanted electrodes on the surface and in the depth of the cortex, field potentials preceding hand movements initiated at self-pace and by visual stimulus were recorded from the premotor cortex and the forelimb areas of motor and somatosensory cortices of the same monkey. A monkey trained with either self-paced or visually initiated movement of a common motor performance revealed the premovement cortical potentials characteristic of the movement, which were markedly distinguishable between the differently initiated movements. When a monkey well-trained with one of the two movements was subsequently trained with the other, it still showed the premovement cortical potentials characteristic of the previous movement at an early stage of training and then later came gradually to reveal the premovement potentials characterized with the latter movement. After sufficient sequential training with each type of movement, the monkey was able to elicit the two kinds of premovement cortical potentials respectively on self-paced and visually initiated movements in successive sessions of the same day. We suggest that the central nervous mechanisms (programs) of preparing self-paced (“voluntary”) and visually initiated (reaction) movements with a common motor performance are very different in the same monkey, and that they can be switched from one to the other after the mechanisms have been reliably established by sufficient training with the two types of movements.     

Human cerebral potentials associated with REM sleep rapid eye movements: links to PGO waves and waking potentials

Eye movement triggered averaging and topographic display techniques indicate the presence of parieto-occipital potentials that precede the rapid eye movements of human REM sleep. Since these potentials have strong similarities with PGO waves in animals, including lateralization according to eye movement (EM) direction, and with waking EM-antecedent potentials in man, this suggests that PGO-like activity both exists in man, and may be functionally related to EM-antecedent potentials in waking. The ability to detect such central potentials opens the possibility of studying REM sleep central physiological structure in a variety of normal and pathological conditions in humans.     

Movement-related potentials and control of associated movements

Previous studies have shown a relationship of the readiness potential (RP) preceding a motor act to motor control, as indexed by eye movement (EM). Greater EM and, therefore, less motor control was associated with increased positivity in preresponse RP components. It was hypothesized that these positive components may reflect processes involved in the inhibition of extraneous or associated movement during the performance of a motor act, especially in younger subjects with less motor development. We developed a finger lift task for detecting irrelevant associated movements (AM) from the responding hand and the nonresponding contralateral hand. During each target finger lift, small movements of the other nontarget fingers from the target hand and the contralateral hand were considered movements that should have been inhibited. Trials for each subject were divided into two bins: associated movement (AM) trials which had movement of target plus nontarget fingers, and trials with only target finger movement detected (NAM). Difference waveforms indicated a positive-going shift on trials with discrete target finger movements (NAM). Age and RP positivity at ipsilateral and posterior regions were significantly correlated. We suggest that, on trials on which associated movements are successfully inhibited, the negativity of the RP is confounded by an overlapping slow positivity. The positivity may be related to the effort needed to inhibit associated movements in order to perform a sharper and more discrete response. This relationship is a function of motor control and, indirectly, of age.