Learning-based animal models: task-specific focal hand dystonia.

Dystonia is a disabling, involuntary disorder of movement that leads to writhing, twisting end-range movements or abnormal postures. Inadequate inhibition could account for excessive excitation and near synchronous co-contractions of agonists and antagonists. Dystonia may be generalized or specific, affecting only one part of the body or involving only a well-learned task (e.g., writing, keyboarding, golfing, playing a musical instrument). Task-specific and other focal dystonias are considered idiopathic, with multiple factors such as genetics, anatomy, physiology, psychology, environment, and behavioral characteristics contributing to the development of symptoms. This article provides detailed descriptions of two behavioral animal models (a primate [owl monkey] model and a rodent [Sprague-Dawley rat] model) developed to study the effect of excessive repetition as a potential etiology of focal hand dystonia (FHd). The hypothesis is that repetitive, near simultaneous hand movements can degrade the topographic representations of the hand on the somatic sensory and motor cortices, creating the involuntary movements characteristic of dystonia. While animal studies permit the opportunity for greater control to determine efficacy, the findings must always be confirmed by clinical studies to evaluate sensitivity and specificity of diagnosis and effectiveness of treatment in the home, work, and personal environment. This article presents a review of the etiology and clinical implications for intervention strategies from animal and clinical studies that support learning-based mechanisms for FHd. Other animal models are also briefly reviewed.