What can we learn from animal models of focal hand dystonia?

Focal hand dystonia (FHd) is a disabling disorder of hand control characterized by a loss of inhibition and involuntary co-contractions of agonists and antagonists that can develop in motivated, productive individuals performing highly repetitive, intensive hand tasks. It is our hypothesis that FHd can result from aberrant learning. We summarize three behavioral animal models (Nancymae aotus owl monkeys and Sprague Dawley rats) that provide evidence supporting aberrant learning as one origin of FHd. Hand task behaviors that increase the risk for repetitive strain injury-FHd include: attended, precise, repetitive behaviors that involve near coincident inputs-outputs (e.g. rapid reversal of agonists-antagonists, stereotypical movements, stressful end range motions, cutaneous stimulation across broad surfaces). High force, vibration, congenital abnormalities, and stress can further increase the risk. The central consequences of aberrant learning include large sensory receptive fields (rfs), significant overlap of rfs across adjacent digits and across glabrous and dorsal surfaces, and the persistence of digital representations across a broad cortical distance (>600 microm). Behavioral animal models are valid for the study of FHd etiology and could logically be applied to study the effects of pharmaceutical, surgical, anatomical, and behavioral enrichment intervention strategies, but these models may have limitations in the study of the recovery of fine motor, articulated, interdigitated movements following progressive, learning based, complex sensorimotor training.