Psychotogenic drugs and delirium pathogenesis: the central role of the thalamus.

Delirium is thought to be a temporary psychiatric disorder resulting from a reduced central cholinergic transmission, combined with an increased dopaminergic transmission. The cholinergic and the dopaminergic systems interact not only with each other but with glutamatergic and gamma-amino-butyric acid (GABA) pathways. Besides the cerebral cortex, critical anatomical substrates of psychosis pathophysiology would comprise the striatum, the substantia nigra/ventral tegmental area, and the thalamus. The thalamus acts as a filter, allowing only the relevant information to travel to the cortex. Drugs of abuse (e.g. PCP, Ecstasy), as well as psychoactive medications frequently prescribed to hospitalized patients (e.g. benzodiazepines, opioids) could compromise the thalamic gating function, leading to sensory overload and hyperarousal. We propose that drug-induced delirium would result from the transient thalamic dysfunction caused by exposure to medications that interfere with central glutamatergic, GABAergic, dopaminergic and cholinergic pathways at critical sites of action. This model provides directions for future studies in neurophysiology, in vivo brain imaging, and psychopharmacology investigating delirium neuropathophysiology.