ABSTRACT
The subcortical degenerative diseases, often called the subcortical dementias, are caused by degeneration of the basal ganglia, i.e. those parts of the brain below the conscious cortex, which have a powerful influence over body movements and muscle tone (Aird 2000). The basal ganglia (see Chapter 1) form part of a loop that regulates motor function (Figure 1.8). This loop starts with the frontal cortex, which projects fibres to the corpus striatum. The striatum has connections with both the globus pallidus and the substantia nigra pars reticulata, which then connect to various nuclei of the thalamus. Finally, the thalamus connects back to the frontal lobe, completing the loop (Figures 1.8, 13.1). Degeneration of any part of this loop can cause both motor symptoms (basal ganglia) and psychotic symptoms (frontal lobe). Central to the production of symptoms in these disorders is the disturbance to dopamine metabolism. Dopamine depletion in the basal ganglia causes motor deficits, while dopamine problems in the frontal lobes generate cognitive and psychotic symptoms.
