[Satellite systems of the basal ganglia--anatomic position, clinical relevance]

The interaction of basal ganglia and other brain regions is more complex regarding anatomic and functional perspectives than previously assumed. Hence, the classical basal ganglia model has to be extended to at least four satellite systems modulating motor-executive, associative and limbic-motivational brain regions: (i) an indirect projection system, (ii) a striato-nigro-striatal loop, (iii) a "hyperdirect" projection system as well as additional projections to the subthalamic nucleus and (iv) multisynaptic connections from the cerebellum exerting influence on the indirect projection system. The investigation of these satellite systems would be invaluable to foster our understanding of basal ganglia circuitries and may yield a better appreciation of largely opaque symptoms like resting tremor in Parkinson's disease; analysis of these anatomic pathways and functional implications may facilitate explanatory model approaches to side effects due to dopaminergic therapy and deep brain stimulation in humans and thereby offer the possibility for new therapeutic approaches in movement disorders.