Abstract
Our movements are shaped by our perception of the world as communicated by our senses. Perception of sensory information has been largely attributed to cortical activity. However, a prior level of sensory processing occurs in the spinal cord. Indeed, sensory inputs directly project to many spinal circuits, some of which communicate with motor circuits within the spinal cord. Therefore, the processing of sensory information for the purpose of ensuring proper movements is distributed between spinal and supraspinal circuits. The mechanisms underlying the integration of sensory information for motor control at the level of the spinal cord have yet to be fully described. Recent research has led to the characterization of spinal neuron populations that share common molecular identities. Identification of molecular markers that define specific populations of spinal neurons is a prerequisite to the application of genetic techniques devised to both delineate the function of these spinal neurons and their connectivity. This strategy has been used in the study of spinal neurons that receive tactile inputs from sensory neurons innervating the skin. As a result, the circuits that include these spinal neurons have been revealed to play important roles in specific aspects of motor function. We describe these genetically identified spinal neurons that integrate tactile information and the contribution of these studies to our understanding of how tactile information shapes motor output. Furthermore, we describe future opportunities that these circuits present for shedding light on the neural mechanisms of tactile processing.
Highlights
THE NEURAL CONTROL OF MOTOR activity is a product of signals arising from three main sources: supraspinal centers, spinal networks, and peripheral sensory afferents
When fine motor control during locomotion was accessed by the raised beam test (Crawley 2008), a significant increase in hindlimb missteps was reported. These results suggest that ROR␣ INs mediate cutaneous sensory information for use in motor commands involved in corrective foot movements
To shape motor control through an integration of tactile information, these spinal INs must project a set of instructive motor commands. We suggest that these motor commands diverge to activate spinal circuits or motor modules dedicated to specific aspects of motor control (Giszter and Hart 2013)
Summary
Pax Irx Pax Ngn Pax Msx Ascl Gsh Olig3Isl IsTl1lx TDlxr3g11DrBgm113aBrn3a/b dI3. LVST neurons are known to originate in the pons and project downwards to the spinal cord carrying information about posture and balance (Markham 1987) These results demonstrate that ROR␣ INs are spinal neurons that are implicated in integrating tactile inputs to shape motor activity (Fig. 1C). When fine motor control during locomotion was accessed by the raised beam test (Crawley 2008), a significant increase in hindlimb missteps was reported These results suggest that ROR␣ INs mediate cutaneous sensory information for use in motor commands involved in corrective foot movements. The recent studies of genetically defined spinal INs that we have described (summarized in Fig. 1) build on the work of the past decades and serve
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