Disorders of the basal ganglia and their modern management.

Fig 1. Major neuronal pathways w ithin the basal ganglia in a) a normal individual and b) an individual w ith Parkinson' s disease (much simplified illustrations). In crude terms, the substantia nigra pars compacta (SNPC) may be regarded as an ' accelerator' for movement, and the subthalamic nucleus (STN) and internal pallidum (GPI)/substantia nigra pars reticulata (SNPR) as ' brakes' . The consequence of nigral cell loss in Parkinson' s disease is to ' remove the foot from the accelerator' which, along the line in the outflow pathways, results in ' braking' of the ventrolateral thalamus (VL THAL) and hence of the motor cortex (CS = corpus striatum (putamen and caudate); DA = dopamine; D 1 and D2 = dopamine receptors; GABA = gamma-aminobutyric acid; GPE = external pallidum; + = excitation; — = inhibition; green = inhibitory pathways; mauve = excitatory pathways). (Adapted from Ref 3.) a