A primate model for studying focal dystonia and repetitive strain injury: effects on the primary somatosensory cortex.

BACKGROUND AND PURPOSE Job-related repetitive strain injuries (RSIs) are increasing, and current treatment strategies often fail to return injured people to work. This study documented the neural consequences of using two different movement strategies for active, repetitive hand closing and opening. METHODS Two owl monkeys were trained for 20 weeks to repetitively close a handpiece against an 80-g force (3-400 trials per day, training at 80%-90% accuracy). One monkey used a highly articulated hand-squeezing strategy, and the other monkey used a proximal arm-pulling strategy. Changes in motor performance were analyzed, and the electrophysiological maps of the hand representation on the trained primary sensory cortex (area 3b) were compared with those of untrained control animals and the untrained sides of the trained monkeys. RESULTS The monkey using the articulated hand-squeezing strategy showed motor deterioration and dedifferentiation of the normally sharply segregated areas of the hand representation in area 3b. Mild degradation of the hand representation was measured in the monkey using the proximal arm-pulling strategy, but there was no motor dysfunction. CONCLUSION AND DISCUSSION Attended, highly articulated, repetitive finger squeezing degrades the hand representation and interferes with motor control. A proximal, more variable repetitive strategy minimized the sensory degradation and preserved motor control. Restoring the hand representation may be a critical part of treatment for patients with chronic RSI and focal hand dystonia.