title: The relationship between brain activity and peak grip force is modulated by corticospinal system integrity after subcortical stroke.
abstract: In healthy human subjects, the relative contribution of cortical regions to motor performance varies with the task parameters. Additionally, after stroke, recruitment of cortical areas during a simple motor task varies with corticospinal system integrity. We investigated whether the pattern of motor system recruitment in a task involving increasingly forceful hand grips is influenced by the degree of corticospinal system damage. Nine chronic subcortical stroke patients and nine age-matched controls underwent functional magnetic brain imaging whilst performing repetitive isometric hand grips. Target grip forces were varied between 15% and 45% of individual maximum grip force. Corticospinal system functional integrity was assessed with transcranial magnetic stimulation. Averaged across all forces, there was more task-related activation compared with rest in the secondary motor areas of patients with greater corticospinal system damage, confirming previous reports. However, here we were primarily interested in regional brain activation, which covaried with the amount of force generated, implying a prominent executive role in force production. We found that in control subjects and patients with lesser corticospinal system damage, signal change increased linearly with increasing force output in contralateral primary motor cortex, supplementary motor area and ipsilateral cerebellum. In contrast, in patients with greater corticospinal system damage, force-related signal changes were seen mainly in contralesional dorsolateral premotor cortex, bilateral ventrolateral premotor cortices and contralesional cerebellum, but not ipsilesional primary motor cortex. These findings suggest that the premotor cortices might play a new and functionally relevant role in controlling force production in patients with more severe corticospinal system disruption.
authors: Wellcome Department of Imaging Neuroscience, and Department of Brain Repair and Rehabilitation, Institute of Neurology, University College London, London, UK. n.ward@fil.ion.ucl.ac.uk
authors: Nick S
authors: NS
authors: Ward
authors: Jennifer M
authors: JM
authors: Newton
authors: Orlando B C
authors: OB
authors: Swayne
authors: Lucy
authors: L
authors: Lee
authors: Richard S J
authors: RS
authors: Frackowiak
authors: Alan J
authors: AJ
authors: Thompson
authors: Richard J
authors: RJ
authors: Greenwood
authors: John C
authors: JC
authors: Rothwell
mesh_terms: D000328:Adult; D000368:Aged; D001921:Brain / Q000098:blood supply / Q000503:physiopathology*; D001931:Brain Mapping; D016022:Case-Control Studies; D007839:Functional Laterality; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood; D011597:Psychomotor Performance / Q000502:physiology; D011712:Pyramidal Tracts / Q000503:physiopathology*; D020521:Stroke / Q000473:pathology* / Q000503:physiopathology; D050781:Transcranial Magnetic Stimulation / Q000379:methods
chemical_list: D010100:Oxygen