Is there a final common neural pathway in delirium? Focus on acetylcholine and dopamine.

This article reviews the literature relevant to improving our understanding of the neural underpinnings of delirium. That the characteristic symptoms of delirium occur as a result of a wide diversity of causes supports the concept of a common pathway. What constitutes this may involve certain brain regions or circuits and certain neurotransmitters. Neuroanatomical data derived from neuroimaging and lesion reports suggest the importance of pathways in prefrontal cortex, thalamus, fusiform cortex, posterior parietal cortex, and basal ganglia. Neurotransmitters most implicated in delirium that could be candidates to mediate the characteristic symptoms of delirium, as well as the electroencephalogram changes, are acetylcholine and dopamine. Acetylcholine deficiency and dopamine excess---absolute and/or relative to each other---appear to be critical in the final common pathway. These neurotransmitters affect each other, depending on the receptor subtype, and their receptor distribution among layers of cortex in areas such as prefrontal cortex and temporal lobe suggests that cholinergic and dopaminergic neurons could interact with each other during delirium. Electroconvulsive therapy is described as a special situation in which excess dopamine and delirium may have a therapeutic effect on depression recovery, in contrast with the usual association of delirium with negative effects.