ABSTRACT
The subcortical degenerative diseases, often called the subcortical dementias, are included here because, like the cortical dementias (Chapter 14) they sometimes fall into the care of the psychiatric nurse. The reason is that they are often associated with depression and psychoses (Kaplan and Sadock 1996). These disorders are essentially caused by degeneration of the basal ganglia, those parts of the brain below the conscious cortex that have a powerful infl uence over body movements and muscle tone (Aird 2000). The basal ganglia form part of a loop that regulates motor function. This loop starts with the frontal cortex, which projects fi bres to the corpus striatum. The striatum has connections with both the globus pallidus and the substantia nigra pars reticulum, which then connect to various nuclei of the thalamus. Finally, the thalamus connects back to the frontal lobe, completing the loop (Figure 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 defi cits, while dopamine problems in the frontal lobes generate cognitive and psychotic symptoms.
