title: Abnormal surround inhibition does not affect asymptomatic limbs in people with cervical dystonia.
abstract: Surround inhibition is a neural mechanism hypothesized to facilitate goal-directed action by disinhibiting agonist muscle activity while simultaneously inhibiting antagonist and other uninvolved muscle activity. The present study was designed to investigate if abnormalities in surround inhibition are found in asymptomatic body parts (the hand) of people with focal cervical dystonia (neck). Participants with (n=7) and without (n=17) cervical dystonia completed a protocol in which they abducted their index finger while EMG was recorded from the first dorsal interosseous (agonist) and abductor digiti minimi (uninvolved) muscles. Transcranial magnetic stimulation was delivered over the primary motor cortex at intervals ranging from 0 to 950+ms after the onset of agonist muscle activity. Motor-evoked potential (MEP) amplitudes from both muscles were compared. In control participants, MEPs from the uninvolved muscle were significantly lower than agonist MEPs at intervals from 0 to 480ms. Similarly, in the hands of participants with cervical dystonia - the asymptomatic body part - MEPs from the uninvolved muscle were significantly lower than agonist MEPs from 0 to 175ms. These findings suggest that surround inhibition in people with focal dystonia may be intact in asymptomatic hands. In other words, abnormalities in surround inhibition may be restricted to the dystonic limb.
authors.affiliation: Faculty of Kinesiology, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada.
authors.forename: Laura
authors.initials: L
authors.lastname: McDougall
authors.affiliation: Faculty of Kinesiology and Physical Education, University of Toronto, 55 Harbord Street, Toronto, ON M5S 2W6, Canada; Department of Kinesiology, University of Maryland, SPH Building, College Park, MD 20742, USA.
authors.forename: Dovin
authors.initials: D
authors.lastname: Kiernan
authors.affiliation: Department of Clinical Neurosciences and Hotchkiss Brain Institute, University of Calgary, Health Research Innovation Centre, Room 1A10, 3330 Hospital Drive NW, Calgary, AB T2N 4N1, Canada.
authors.forename: Zelma H T
authors.initials: ZH
authors.lastname: Kiss
authors.affiliation: Departments of Medicine, Pediatrics and Medical Genetics, University of Alberta, 13-103 Clinical Sciences Building, 11350 - 83 Avenue, Edmonton, AB T6G 2G3, Canada.
authors.forename: Oksana
authors.initials: O
authors.lastname: Suchowersky
authors.affiliation: Faculty of Kinesiology and Physical Education, University of Toronto, 55 Harbord Street, Toronto, ON M5S 2W6, Canada; Centre for Motor Control, University of Toronto, 55 Harbord Street, Toronto, ON M5S 2W6, Canada. Electronic address: t.welsh@utoronto.ca.
authors.forename: Timothy N
authors.initials: TN
authors.lastname: Welsh
mesh_terms: D000368:Aged; D004576:Electromyography; D005260:Female; D006225:Hand / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000503:physiopathology; D009433:Neural Inhibition; D014103:Torticollis / Q000503:physiopathology*; D050781:Transcranial Magnetic Stimulation
keywords: Cervical dystonia; Dystonia; Motor control; Surround inhibition; Transcranial magnetic stimulation