Movement-related cortical potentials associated with voluntary muscle relaxation

Activities of the primary and supplementary motor areas increase in preparation and execution of voluntary muscle relaxation: an event-related fMRI study

Brain activity associated with voluntary muscle relaxation was examined by applying event-related functional magnetic resonance imaging (fMRI) technique, which enables us to observe change of fMRI signals associated with a single motor trial. The subject voluntarily relaxed or contracted the right upper limb muscles. Each motor mode had two conditions; one required joint movement, and the other did not. Five axial images covering the primary motor area (M1) and supplementary motor area (SMA) were obtained once every second, using an echoplanar 1.5 tesla MRI scanner. One session consisted of 60 dynamic scans (i.e., 60 sec). The subject performed a single motor trial (i.e., relaxation or contraction) during one session in his own time. Ten sessions were done for each task. During fMRI scanning, electromyogram (EMG) was monitored from the right forearm muscles to identify the motor onset. We calculated the correlation between the obtained fMRI signal and the expected hemodynamic response. The muscle relaxation showed transient signal increase time-locked to the EMG offset in the M1 contralateral to the movement and bilateral SMAs, where activation was observed also in the muscle contraction. Activated volume in both the rostral and caudal parts of SMA was significantly larger for the muscle relaxation than for the muscle contraction (p < 0.05). The results suggest that voluntary muscle relaxation occurs as a consequence of excitation of corticospinal projection neurons or intracortical inhibitory interneurons, or both, in the M1 and SMA, and both pre-SMA and SMA proper play an important role in motor inhibition.

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.

Neurophysiology of positive and negative myoclonus

Myoclonus is defined as a sudden, brief, jerky, shock-like, involuntary movement, arising from the central nervous system that can be caused by a muscular contraction, i.e. positive myoclonus, or by an interruption of muscular activity, i.e. negative myoclonus. Myoclonus can characterize a variety of neurological disorders, and often both positive and negative myoclonus can coexist. In this paper, we outline some relevant clinical aspects and neurophysiological features of the different types of myoclonus, with particular emphasis on the physiological findings. Indeed, since most myoclonus depend on enhancement of neuronal activities which are inherently present in normal subjects, electrophysiological studies are useful for elucidating the underlying pathophysiological mechanisms and for establishing the correct diagnosis [corrected].

Human supplementary motor area is active in preparation for both voluntary muscle relaxation and contraction: subdural recording of Bereitschaftspotential

Bereitschaftspotentials (BPs) preceding muscle relaxation and contraction were compared by using subdural electrodes which were implanted onto the right medial frontal surface in two patients with supplementary motor area (SMA) seizure. The applied movement paradigm (muscle relaxation and contraction tasks) was completely the same as employed in our previous study [Terada, K., Ikeda, A., Nagamine, T. and Shibasaki, H., Electroenceph. clin. Neurophysiol., 95 (1995) 335-345]. In both patients, either negative or positive BPs were observed in the SMA-proper and supplementary negative motor area (SNMA) starting at 1.2-1.8 prior to both movements. In one patient, BP was more widespread in the relaxation task whereas more restricted to the hand area in the contraction task. In the other patient, the BPs were observed in the cortical area rostral to SNMA (pre-SMA), in addition to the SMA-proper, in both tasks. It is concluded that SMA-proper and SNMA, and probably pre-SMA as well, in humans are similarly active in preparation for both voluntary muscle contraction and relaxation.

Aberrant muscle activation in patients after resection of non-primary motor areas: demonstration by surface electromyography

Two patients presented with a tumor involving mainly the supplementary motor area or the premotor cortex. Shortly after tumor resection, each developed transient impairment of voluntary movements. An electromyogram, with the skin electrodes placed over the muscles of the upper arms and forearms, demonstrated aberrant ipsilateral, contralateral or bilateral muscle activation during unilateral motor tasks in both patients. The bilateral activation was more prominent in the patient who had an intact dominant hemisphere. The present study suggests for the first time the importance of non-primary motor areas of the human brain in activating the proper set of muscles on the proper side of the body.

The offset cortical potential: an electrical correlate of movement inhibition in man

Nine normal subjects were asked to make either a brisk isometric pinch of a force transducer held between the forefinger and thumb, or to hold a pinch for approximately 15 s and then release the force suddenly without any overt antagonist contraction. EEG activity was averaged about the onset or offset of EMG activity, and movements were made in the subjects' own time. All subjects found the task simple. The EEG activity preceding offset of contraction (offset cortical potential) was significantly smaller in lateral leads than that seen before onset of contraction. Midline activation was similar in both tasks. We suggest that in the onset task, motor cortex activity related to the act to be performed contributes substantially to the EEG potentials in lateral leads. This activity is absent in the offset task which requires only withdrawal of tonic input to motor cortex. Midline activity, common to both onset and offset tasks, could reflect timing, attentional, or other processes. The results are discussed in relation to previous data from an isotonic relaxation task.

Familial cortical myoclonic tremor as a unique form of cortical reflex myoclonus

Previously it was reported that some patients with tremor had the same electrophysiological findings as those seen in patients with cortical reflex myoclonus, and consequently the tremor was named "cortical tremor." In the present study, we examined six patients from three families with cortical tremor of relatively late onset. The inheritance pattern of cortical tremor was compatible with autosomal dominant trait. Those patients had relatively rhythmic involuntary movements (tremor) in the distal upper and lower limbs, especially during posture and/or fine movements. There was no cerebellar ataxia or dementia, and fits of loss of consciousness occurred only infrequently. Electrophysiologically, they had generalized spikes on electroencephalogram (EEG), giant cortical components of somatosensory evoked potential, an enhanced long-loop reflex (C-reflex), and cortical spikes preceding the rhythmic jerk demonstrable by the jerk-locked back averaging method, thus fulfilling the criteria of cortical reflex myoclonus. Furthermore, they had slow negative EEG shift starting 1-2 s prior to voluntary movements, suggesting that, as opposed to the conventional form of progressive myoclonus epilepsy (PME), the cerebellar efferent input to the motor cortices was normal. These clinical and electrophysiological pictures are distinct from those of familial essential tremor, familial essential myoclonus, or the conventional form of PME, and the term "familial cortical myoclonic tremor" will represent the clinical and electrophysiological features of this unique entity most appropriately.