Inhibitory period following motor potentials evoked by magnetic cortical stimulation.

Following motor potentials evoked (MEPs) by magnetic cortical stimulation, there is a transient suppression of muscle action potentials (inhibitory period). We recorded MEPs, the inhibitory period, V1 waves and F waves from the abductor pollicis brevis muscle in 20 normal subjects and in 17 patients with spastic hyperreflexia due to cerebral infarction. The duration of the inhibitory period increased in correspondence with increasing stimulus intensity and did not necessarily depend on the amplitude of the MEPs. The duration of the inhibitory period elicited by a twin coil, which can stimulate the motor cortex locally, was shorter than by a single coil. The mean duration of the inhibitory period was significantly shorter in patients with spastic hyperreflexia than in normal subjects, and it correlated with the amplitude of F waves. The effects of the inhibitory period on V1 waves were different from its effects on F waves in one patient with large V1 and F waves. The amplitudes of V1 waves recorded during the inhibitory period were approximately 30-50% of the maximal amplitude of V1 waves, but F waves were not smaller. The inhibitory period is probably caused primarily by central inhibitory mechanisms.

[1]  K. Mills,et al.  Responses in small hand muscles from magnetic stimulation of the human brain. , 1987, The Journal of physiology.

[2]  A. Barker,et al.  NON-INVASIVE MAGNETIC STIMULATION OF HUMAN MOTOR CORTEX , 1985, The Lancet.

[3]  Jun Kimura,et al.  Electrodiagnosis in Diseases of Nerve and Muscle: Principles and Practice , 1983 .

[4]  P. Thompson,et al.  Motor cortex stimulation in intact man. 2. Multiple descending volleys. , 1987, Brain : a journal of neurology.

[5]  V. Amassian,et al.  Focal stimulation of human cerebral cortex with the magnetic coil: a comparison with electrical stimulation. , 1989, Electroencephalography and clinical neurophysiology.

[6]  Andrew Eisen,et al.  Amplitude of the F wave , 1979, Neurology.

[7]  M. Fisher.  F/M ratios in polyneuropathy and spastic hyperreflexia , 1988, Muscle & nerve.

[8]  C. Marsden,et al.  Transmission in the spinal reciprocal Ia inhibitory pathway preceding willed movements of the human wrist , 1983, Neuroscience Letters.

[9]  C. Marsden,et al.  The effect of percutaneous motor cortex stimulation on H reflexes in muscles of the arm and leg in intact man. , 1986, The Journal of physiology.

[10]  S. Boniface,et al.  Long latency changes in the firing probability of single human motoneurones following magnetic brain stimuli , 1990 .

[11]  V. Amassian,et al.  Suppression of visual perception by magnetic coil stimulation of human occipital cortex. , 1989, Electroencephalography and clinical neurophysiology.

[12]  H. Morton,et al.  Stimulation of the cerebral cortex in the intact human subject , 1980, Nature.

[13]  E. Fetz,et al.  Patterns of facilitation and suppression of antagonist forelimb muscles from motor cortex sites in the awake monkey. , 1985, Journal of neurophysiology.

[14]  Excitatory and inhibitory effects of magnetic coil stimulation of human cortex. , 1990, Electroencephalography and clinical neurophysiology. Supplement.

[15]  B. Day,et al.  AN INVESTIGATION OF THE EMG SILENT PERIOD FOLLOWING STIMULATION OF THE BRAIN IN NORMAL MAN , 1989 .

[16]  A. McComas,et al.  Potentiation of `late' responses evoked in muscles during effort , 1971, Journal of neurology, neurosurgery, and psychiatry.

[17]  S. Tsuji,et al.  Motor potentials evoked by magnetic stimulation of the motor cortex in normal subjects and patients with motor disorders. , 1991, Electroencephalography and clinical neurophysiology.

[18]  E. Stanley.  Reflexes evoked in human thenar muscles during voluntary activity and their conduction pathways. , 1978, Journal of neurology, neurosurgery, and psychiatry.

[19]  L. Larsson,et al.  Late muscular responses to transcranial cortical stimulation in man. , 1990, Electroencephalography and clinical neurophysiology.

[20]  V E Amassian,et al.  An analysis of the activation of motor cortical neurons by surface stimulation. , 1967, Journal of neurophysiology.

[21]  M Nordin,et al.  Motor-unit responses in human wrist flexor and extensor muscles to transcranial cortical stimuli. , 1987, Journal of neurophysiology.

[22]  P. Thompson,et al.  Motor cortex stimulation in intact man. 1. General characteristics of EMG responses in different muscles. , 1987, Brain : a journal of neurology.

[23]  B. Day,et al.  Electric and magnetic stimulation of human motor cortex: surface EMG and single motor unit responses. , 1989, The Journal of physiology.

[24]  P M Rossini,et al.  Enhancement of motor cortical excitability in humans by non-invasive electrical stimulation appears prior to voluntary movement. , 1988, Electroencephalography and clinical neurophysiology.

[25]  S. Bandinelli,et al.  Effects of coil design on delivery of focal magnetic stimulation. Technical considerations. , 1990, Electroencephalography and clinical neurophysiology.