Quantitative evaluation of the silent period, evoked by transcranial magnetic stimulation during sustained muscle contraction, in normal man and in patients with stroke.
It is well known that transcranial stimulation, delivered during sustained muscle contraction, evokes a temporary suppression of motor activity (silent period). The aim of the present study was to further analyze this inhibition in 20 healthy subjects and in 10 patients with previous stroke. Transcranial magnetic stimulation was performed at the vertex, recording responses from first dorsal interosseus (FDI) muscle. Normative data were provided from the control group. The results indicate a narrow range of onset latency, a wide interindividual variation of duration but small interside differences and a sufficient intraindividual stability. As the duration showed an approximately linear increase with increasing stimulus intensities, a standardized paradigm was employed, applying individually adjusted stimulus strengths of 50% above the threshold able to evoke a silent period. There was no relationship between silent period parameters and 1) age, 2) body length, and 3) innervation force. In the patient group, silent period duration was significantly prolonged when recordings were obtained from the affected side. This finding might prove to be an interesting new parameter in the investigation of motor disturbance due to previous stroke. With regard to the physiological basis of the phenomenon, spinal and cortical influences are discussed.
Kukowski
B
B
Department of Clinical Neurophysiology, University of Goettingen.
Haug
B
B
D000293:Adolescent; D000328:Adult; D000368:Aged; D002561:Cerebrovascular Disorders / Q000503:physiopathology*; D004576:Electromyography; D005260:Female; D006181:H-Reflex / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D050781:Transcranial Magnetic Stimulation