Table 1. Sources of cholinergic dysfunction in PD and its main clinical correlates.

PD feature	Pathological basis	Possible treatment
PD motor symptoms	Altered cholinergic striatal tone	Antimuscarinic drugs in low doses to avoid atropinic side effects
Gait impairment and falls	Degeneration of the NBM and/or the PPN nuclei	To reduce falls: AChE inhibitors and possibly PPN DBS (controversial)
Levodopa-induced dyskinesias	Altered cholinergic striatal tone	Drugs acting on nicotinic receptors (in pre-clinical stages)
Cognitive Impairment	Degeneration of the NBM	AChE inhibitors (proven efficacy)
RBD	Degeneration of the PPN	AChE inhibitors (never tested)
Psychosis	Reduced cholinergic tone (site unknown)	AChE inhibitors (never tested)
Neuroprotection	Mechanism unknown	Drugs acting on nicotinic receptors (in preclinical stages)

Abbreviations: AChE, Acetylcholinesterase enzyme; DBS, deep brain stimulation; NBM, nucleus basalis magnocellularis (Meynert’s nucleus); PD, Parkinson’s disease; PPN, pedunculopontine nucleus; REM, rapid eye movement; RBD, REM-sleep Behavior Disorder.