title: Reduced cortical activity during maximal bilateral contractions of the index finger.
abstract: The bilateral deficit refers to the phenomenon in which homologous muscles produce per muscle less force when contracting simultaneously than when contracting individually. The mechanism underlying the bilateral deficit is still unknown, but the most likely cause is a decline in the activation of motor units during bilateral contractions. In the present study, we used functional magnetic resonance imaging (fMRI) to measure the degree of brain activity during unilateral and bilateral maximal contractions in combination with force and EMG measurements. Subjects performed, in a semi-randomized order, maximal isometric contractions (MVC) with the right index finger, the left index finger and with both fingers simultaneously. During the task, brain activation was measured with a 3 T MR scanner, in combination with force and EMG recordings. The most important activated areas in the brain during the contractions were the sensorimotor cortex (precentral and postcentral gyrus), cerebellum, premotor cortex and supplementary motor area. During bilateral contractions, a significant decline in force and EMG values was found and detailed analysis of the brain activation data showed that this decline was accompanied with a significant decline in the activation of the precentral gyrus. This result suggests that the bilateral decline is the resultant of a decline in input to the primary motor area and shows that the main source of the bilateral deficit lies upstream of the primary motor cortex.
authors.affiliation: Department of Medical Physiology, University Medical Center Groningen, University of Groningen, The Netherlands. Mpost@med.umcg.nl <Mpost@med.umcg.nl>
authors.forename: Marijn
authors.initials: M
authors.lastname: Post
authors.forename: Hiske
authors.initials: H
authors.lastname: van Duinen
authors.forename: Anneke
authors.initials: A
authors.lastname: Steens
authors.forename: Remco
authors.initials: R
authors.lastname: Renken
authors.forename: Bart
authors.initials: B
authors.lastname: Kuipers
authors.forename: Natasha
authors.initials: N
authors.lastname: Maurits
authors.forename: Inge
authors.initials: I
authors.lastname: Zijdewind
mesh_terms: D000328:Adult; D019540:Area Under Curve; D002531:Cerebellum / Q000098:blood supply / Q000502:physiology; D002540:Cerebral Cortex / Q000098:blood supply / Q000502:physiology*; D003627:Data Interpretation, Statistical; D004576:Electromyography; D005260:Female; D005385:Fingers / Q000294:innervation / Q000502:physiology*; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D009044:Motor Cortex / Q000098:blood supply / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology; D010100:Oxygen / Q000097:blood; D012039:Regional Blood Flow / Q000502:physiology; D013238:Stereotaxic Techniques
chemical_list: D010100:Oxygen