Changes in short afferent inhibition during phasic movement in focal dystonia.
Impaired surround inhibition could account for the abnormal motor control seen in patients with focal hand dystonia, but the neural mechanisms underlying surround inhibition in the motor system are not known. We sought to determine whether an abnormality of the influence of sensory input at short latency could contribute to the deficit of surround inhibition in patients with focal hand dystonia (FHD). To measure digital short afferent inhibition (dSAI), subjects received electrical stimulation at the digit followed after 23 ms by transcranial magnetic stimulation (TMS). Motor evoked potentials (MEPs) were recorded over abductor digiti minimi (ADM) during rest and during voluntary phasic flexion of the second digit. F-waves were also recorded. We studied 13 FHD patients and 17 healthy volunteers. FHD patients had increased homotopic dSAI in ADM during flexion of the second digit, suggesting that this process acts to diminish overflow during movement; this might be a compensatory mechanism. No group differences were observed in first dorsal interosseous. Further, no differences were seen in the F-waves between groups, suggesting that the changes in dSAI are mediated at the cortical level rather than at the spinal cord. Understanding the role of these inhibitory circuits in dystonia may lead to development of therapeutic agents aimed at restoring inhibition.
Human Motor Control Section, National Institute of Neurological Disorders and Stroke, National Institutes of Health, 10 Center Drive MSC 1428, Bldg. 10, Bethesda, MD 20892-1428, USA.
Sarah Pirio
SP
Richardson
Barbara
B
Bliem
Mikhail
M
Lomarev
Ejaz
E
Shamim
Nguyet
N
Dang
Mark
M
Hallett
D000328:Adult; D000344:Afferent Pathways / Q000502:physiology / Q000528:radiation effects; D000704:Analysis of Variance; D020821:Dystonic Disorders / Q000503:physiopathology*; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography / Q000379:methods; D019054:Evoked Potentials, Motor / Q000502:physiology*; D005260:Female; D006225:Hand; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement / Q000502:physiology*; D009433:Neural Inhibition / Q000502:physiology* / Q000528:radiation effects; D011930:Reaction Time / Q000502:physiology* / Q000528:radiation effects; D050781:Transcranial Magnetic Stimulation / Q000379:methods