The functional neuroanatomy of dystonia

Abstract

Dystonia is a neurological disorder characterized by involuntary twisting movements and postures. There are many different clinical manifestations, and many different causes. The neuroanatomical substrates for dystonia are only partly understood. Although the traditional view localizes dystonia to basal ganglia circuits, there is increasing recognition that this view is inadequate for accommodating a substantial portion of available clinical and experimental evidence. A model in which several brain regions play a role in a network better accommodates the evidence. This network model accommodates neuropathological and neuroimaging evidence that dystonia may be associated with abnormalities in multiple different brain regions. It also accommodates animal studies showing that dystonic movements arise with manipulations of different brain regions. It is consistent with neurophysiological evidence suggesting defects in neural inhibitory processes, sensorimotor integration, and maladaptive plasticity. Finally, it may explain neurosurgical experience showing that targeting the basal ganglia is effective only for certain subpopulations of dystonia. Most importantly, the network model provides many new and testable hypotheses with direct relevance for new treatment strategies that go beyond the basal ganglia. This article is part of a Special Issue entitled "Advances in dystonia".

Figure 1

Schematic representation of anatomical substrates for dystonia. Panel A shows the most commonly assumed model that involves defects in subcortical pathways of the basal ganglia or cerebellum being transmitted through the cerebral cortex for final expression of dystonia. Panel A also shows the recently appreciated subcortical communications between the basal ganglia and cerebellum (modified from Bostian & Strick, 2010). This schematic has been simplified and does not show all known connections. Solid lines depict well-established direct pathways, and dashed lines depict established pathways involving one or more connections to reach target. Panel B shows an alternative schematic whereby cervical dystonia may be expressed directly through subcortical pathways, such as the interstitial nucleus of Cajal (INC). In this pathway, the cerebral cortex may contribute to the expression of cervical dystonia but the INC is the final common pathway with direct connections to neck motor neurons (modified from Fukushima 2000). These two schematics provide two example of how pathways may differ according to type of dystonia, and how they may not require involvement of the cerebral cortex.