title: Age- and time-dependent effects on functional outcome and cortical activation pattern in patients with median nerve injury: a functional magnetic resonance imaging study.
abstract: OBJECTIVE
  The authors conducted a study to determine age- and time-dependent effects on the functional outcome after median nerve injury and repair and how such effects are related to changes in the pattern of cortical activation in response to tactile stimulation of the injured hand.
  
  
  METHODS
  The authors studied 11 patients with complete unilateral median nerve injury at the wrist repaired with epineural suture. In addition, 8 patients who were reported on in a previous study were included in the statistical analysis. In the entire study cohort, the mean age at injury was 23.3 +/- 13.4 years (range 7-57 years) and the time after injury ranged from 1 to 11 years. Sensory perception was measured with the static 2-point discrimination test and monofilaments. Functional MR imaging was conducted during tactile stimulation (brush strokes) of Digits II-III and IV-V of both hands, respectively.
  
  
  RESULTS
  Tactile sensation was diminished in the median territory in all patients. The strongest predictor of 2-point discrimination was age at injury (p < 0.0048), and when this was accounted for in the regression analysis, the other age- and time-dependent predictors had no effect. The activation ratios (injured/healthy hand) for Digit II-III and Digit IV-V stimulation were positively correlated (rho 0.59, p < 0.011). The activation ratio for Digit II-III stimulation correlated weakly with time after injury (p < 0.041). The activation ratio of Digits IV-V correlated weakly with both age at injury (p < 0.048) and time after injury (p < 0.033), but no predictor reached significance in the regression model. The mean ratio of ipsi- and contralateral hemisphere activation after stimulation of the injured hand was 0.55, which was not significantly different from the corresponding ratio of the healthy hand (0.66).
  
  
  CONCLUSIONS
  Following a median nerve injury (1-11 years after injury) there may be an initial increase in the volume of the cortical representation, which subsequently declines during the restoration phase. These dynamic changes may involve both median and ulnar nerve cortical representation, because both showed negative correlation with time after injury. These findings are in agreement with animal studies showing that cortical plasticity is an important mechanism for functional recovery after peripheral nerve injury and repair.
authors.affiliation: Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden. lotta.b.fornander@lio.se
authors.forename: Lotta
authors.initials: L
authors.lastname: Fornander
authors.forename: Torbjörn
authors.initials: T
authors.lastname: Nyman
authors.forename: Thomas
authors.initials: T
authors.lastname: Hansson
authors.forename: Mattias
authors.initials: M
authors.lastname: Ragnehed
authors.forename: Tom
authors.initials: T
authors.lastname: Brismar
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000503:physiopathology*; D015331:Cohort Studies; D004292:Dominance, Cerebral / Q000502:physiology; D005260:Female; D005385:Fingers / Q000294:innervation*; D005500:Follow-Up Studies; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008475:Median Nerve / Q000293:injuries* / Q000503:physiopathology / Q000601:surgery*; D020423:Median Neuropathy / Q000503:physiopathology* / Q000601:surgery*; D008866:Microsurgery; D008875:Middle Aged; D009416:Nerve Regeneration / Q000502:physiology*; D009473:Neuronal Plasticity / Q000502:physiology*; D012016:Reference Values; D012684:Sensory Thresholds / Q000502:physiology; D013997:Time Factors; D014110:Touch / Q000502:physiology*; D014954:Wrist Injuries / Q000503:physiopathology / Q000601:surgery*; D055815:Young Adult