Relative Contribution of Proprioceptive and Vestibular Sensory Systems to Locomotion: Opportunities for Discovery in the Age of Molecular Science

Abstract

Locomotion is a fundamental animal behavior required for survival and has been the subject of neuroscience research for centuries. In terrestrial mammals, the rhythmic and coordinated leg movements during locomotion are controlled by a combination of interconnected neurons in the spinal cord, referred as to the central pattern generator, and sensory feedback from the segmental somatosensory system and supraspinal centers such as the vestibular system. How segmental somatosensory and the vestibular systems work in parallel to enable terrestrial mammals to locomote in a natural environment is still relatively obscure. In this review, we first briefly describe what is known about how the two sensory systems control locomotion and use this information to formulate a hypothesis that the weight of the role of segmental feedback is less important at slower speeds but increases at higher speeds, whereas the weight of the role of vestibular system has the opposite relation. The new avenues presented by the latest developments in molecular sciences using the mouse as the model system allow the direct testing of the hypothesis.

Keywords: locomotion; molecular sciences; somatosensory feedback; speed; vestibular feedback.

Figure 1

Summary of the somatosensory and vestibular sensory pathways and their integration into the brain and spinal cord.

Figure 2

Summary of the molecular genetic strategies that can be used to dissect the locomotor circuitry. Gene knockouts (top line) can lead to circuit rearrangements that can be combined with several techniques to analyze the function of that circuit (right). Similarly, gene expression can be used to tag populations of neurons and probe their functions via manipulations of their activity or by tracing their synaptic inputs. Fl. protein = fluorescent protein.