Abnormal internal movement representation in writer's cramp

Functional neuroimaging has largely been used to investigate brain pathologies. Regional signal changes associated with neuronal activity can be detected with functional MRI (fMRI) using blood oxygen level–dependent (BOLD) contrast. Functional MRI signal changes during neuronal activation indirectly reflect regional cerebral blood flow and oxygen use by active neurons. Functional MRI can therefore reveal alterations in large-scale brain networks. In dystonia, fMRI during movement performance has shown activation changes in motor-related networks. Tasks that do or do not induce dystonia must be distinguished, as movement performance is an important factor that can influence fMRI activation levels. Tasks that induced dystonia were likely to show fMRI activation changes related to dystonic motor output, compensatory strategies, or altered somatosensory feedback. Activation observed during tasks that did not induce dystonia may be considered primary changes in the brain or secondary long-standing consequences of dystonia. The most commonly affected regions in functional imaging studies included primary and secondary sensorimotor-related regions of the cerebral cortex, the basal ganglia, the thalamus, and the cerebellum (review in ref. 1). Dystonic movements were commonly associated with overactivation in the sensorimotor cortex, whereas activation levels were normal or decreased during nondystonic movements. Altered sensory processing and distorted primary sensory representation were also reported. Reduced sensorimotor activation also occurred during dystonic movements. Movement imagination provides information on movement representation. Compared with movement execution, signal changes observed during movement imagination tasks can potentially reveal primary changes in dystonic patients, without contamination by motor output or distorted afferent feedback. Motor imagery can be used to study representational aspects of movement in the mind. Many studies have shown that there is a remarkable parallelism between motor imagery and motor execution using either mental chronometry tasks or functional imaging tasks. Functional imaging studies have demonstrated that many brain regions are active during both overt movement execution and movement imagination and that these tasks share common neuronal circuitry. Motor imagery studies have also shown that movement representation involves parieto-premotor regions. The parietal cortex is particularly involved in the storage of motor representations and the generation of internal models of movements. Several reports have suggested that in writer’s cramp patients, the internal representation of movement may be altered. Clinical deficits were observed during mental hand rotation and rubber hand illusion tasks. In the current issue of Movement Disorders is an article by Castrop and colleagues, who used fMRI during a kinesthetic motor imagination task to investigate internal movement representation in patients with writer’s cramp. They examined patients while drawing simple geometric figures and during passive observation of videos of hands drawing identical figures. The passive observation task was used to separate potential deficits of internal movement simulation from visual aspects of action matching. The authors report that patients showed deficient sensorimotor activation during the imagination task, whereas the observation task was not affected. This study provides interesting new findings concerning internal movement representation in patients with writer’s cramp. First, they show that patients presented abnormal movement simulation and planning during imagination of hand movements. Regions showing activation changes included the medial (caudal parts of the supplementary motor area) and left ------------------------------------------------------------