Forebrain control of locomotor behaviors

Abstract

Activation of different areas in the forebrain evokes different types of goal directed adaptive behaviors. An important component of these different patterns of behavior is the locomotion that brings the animal to or away from a particular location.Here I review the role of projections from forebrain structures to the mesopontine tegmentum of the brainstem where neural mechanisms for initiation of locomotion and regulation of postural muscle tone are located that are activated during locomotor behavior. It is interesting is to understand how signals that converge from the forebrain structures to the mesopontine tegmentum control locomotor behavior, because the mesopontine tegmentum receives inhibitory efferents from the basal ganglia and excitatory efferents from the limbic-hypothalamic system and the neocortex. Here I hypothesize that the mesopontine tegmentum has functional gating mechanisms that determine whether the subject will initiate and select volitionally-guided or emotionally-triggered locomotor behaviors, depending on the behavioral context.

Simple cellular and network control principles govern complex patterns of motor behavior

“…The direct control is exerted by evolutionary conserved locomotor command regions (MLR) that via reticulospinal neurons (RS) directly regulate the level of activity in the spinal CPG. The level of activity in these command regions is, in turn, under the control of the basal ganglia (striatum and pallidum), through a selective and gradual release from tonic inhibition (30,31). Stimulation of the lamprey striatum can elicit locomotion, and the locomotor command regions are known to be under tonic inhibition at rest (30).…”

“…3B results, in turn, from a removal of inhibitory activity from the modeled output stage of the basal ganglia (pallidum). Biologically, it is well documented that these inhibitory neurons are spontaneously active under resting conditions and that they target the locomotor command regions from lamprey to mammals and that an experimental blockade of the tonic inhibition releases locomotor activity (30,31). We have included the basal ganglia control by modeling the pallidal output neurons (n ϭ 300), spontaneously active at rest, and the striatal (n ϭ 3000) neurons being silent at rest.…”

Possible Contribution of the Basal Ganglia Brainstem System to the Pathogenesis of Parkinson’s Disease

“…Motor behaviors require the recruitment of the activities of the entire nervous system (Fig.1A) and musculoskeletal systems (Fig.1B). Sensory signals, derived from both external stimuli and internal visceral information (Fig.1Aa), have the following dual functions (Takakusaki, 2008). One is to generate cognitive information processing that is utilized for working memory to guide future behavior (Fig.1Ab).…”

“…Another may affect the emotional and arousal states (Fig.1Ac). Accordingly, animals initiate movements depending on either a "volitional or cognitive reference" or an "emotional reference" (Takakusaki 2008 behaviors therefore may require following the three processes; "volitional process" (Fig.1A(1)), " emotional process" (Fig.1A(2)) and "automatic processes" (Fig.1A(3)). The volitional process is derived from intentionally-elicited motor commands arising from the cerebral cortex based on volitional and cognitive references.…”

“…On the contrary the excitability of the muscle tone inhibitory system may be higher than that of the locomotor system in the absence of orexin. Accordingly GABAergic projection from the SNr to the PPN/MLR area (BG-BS system) may underlie orexin-mediated vigilance state regulation and its dysfunction may be one of pathophysiological mechanisms of narcolepsy-like features of PD (Takakusaki 2008).…”