title: The effects of stroke and age on finger interaction in multi-finger force production tasks.
abstract: OBJECTIVE
  The main purpose of this study was to investigate changes in finger interaction after stroke with strongly unilateral motor effects. Effects of age on finger interaction were also analyzed.
  
  
  METHODS
  Sixteen stroke subjects and 16 control subjects produced maximal voluntary contractions with different finger combinations by one hand and by two hands simultaneously. Individual finger forces were measured. In multi-finger tasks, force deficit (FD) was quantified as the difference between the peak finger forces in single-finger tasks and in multi-finger tasks, while enslaving (ENSL) was quantified as forces produced by fingers that were not required to produce force.
  
  
  RESULTS
  In stroke subjects, the peak forces produced by the fingers of the impaired hand (IH) were about 36% less than those produced by the unimpaired hand. Stroke resulted in higher ENSL and decreased FD in the IH, particularly when the index and middle fingers produced force together, while aging led to higher FD and no change in ENSL. Two-hand tasks were accompanied by an additional drop in the force of individual fingers, i.e. bilateral deficit (BD). No changes in BD were observed with age or after stroke.
  
  
  CONCLUSIONS
  We conclude that IH function in persons after stroke is accompanied not only by a general loss of finger force but also by changes in indices of multi-finger interaction. The contrast between the significantly changed indices of one-hand multi-finger interaction and unchanged BD implies that cortical neurons mediating interhemispheric inhibition are relatively spared in unilateral stroke.
  
  
  CONCLUSIONS
  The study shows that stroke leads to changes not only in finger force but also in finger interaction. The conclusion on relatively spared interhemispheric projections is potentially important for therapy of hand function in stroke survivors.
authors.affiliation: Department of Kinesiology, Recreation Hall-267, Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Sheng
authors.initials: S
authors.lastname: Li
authors.forename: Mark L
authors.initials: ML
authors.lastname: Latash
authors.forename: Guang H
authors.initials: GH
authors.lastname: Yue
authors.forename: Vlodek
authors.initials: V
authors.lastname: Siemionow
authors.forename: Vinod
authors.initials: V
authors.lastname: Sahgal
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D005260:Female; D005385:Fingers / Q000502:physiology*; D007839:Functional Laterality; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D008875:Middle Aged; D009048:Motor Skills; D009068:Movement; D009119:Muscle Contraction; D011597:Psychomotor Performance; D020521:Stroke / Q000150:complications / Q000503:physiopathology*