Here we review a role of a basal ganglia–brainstem (BG–BS) system throughout the mesopontine tegmentum in the control of various types of behavioral expression. First the basal ganglia–brainstem system may contribute to an automatic control of movements, such as rhythmic limb movements and adjustment of postural muscle tone during locomotion, which occurs in conjunction with voluntary control processes. Second, the basal ganglia–brainstem system can be involved in the regulation of awake–sleep states. We further propose the possibility that the basal ganglia–brainstem system is responsible for the integration of volitionally-guided and emotionally-triggered expression of motor behaviors. It can be proposed that dysfunction of the basal ganglia–brainstem system together with that of cortico-basal ganglia loop underlies the pathogenesis of behavioral disturbances expressed in basal ganglia dysfunction.
