**4. Disturbances of non-motor functions in Parkinson's disease**

Disturbances in cognitive and psychotic processes have been observed in patients with degenerative disorders that involve primarily the basal ganglia such as PD (Mellers et al., 1995; Taylor et al., 1986) and HD (McHugh & Folsten, 1975). Awake-sleep states were also impaired in PD (Bliwise et al., 2000; Eisensehr et al., 2001). It is also reported that PD is preceded and accompanied by daytime sleep attacks, nocturnal insomnia, REM sleep behavior disorder, hallucinations and depression, symptoms which are frequently as troublesome as the motor symptoms of this disease. All these symptoms are present in narcolepsy (Thannical et al., 2007). These clinical evidences corroborate that the basal ganglia and their connections with the brainstem are also involved in the expression of nonmotor function. In this section, we focus on the roles played by the BG-BS system in the regulation of vigilance states, arousal state, attention and cognition in relation to non-motor symptoms in PD.
