Abstract
It is generally assumed that the main function of the corticospinal tract (CST) is to convey motor commands to bulbar or spinal motoneurons. Yet the CST has also been shown to modulate sensory signals at their entry point in the spinal cord through primary afferent depolarization (PAD). By sequentially investigating different routes of corticofugal pathways through electrophysiological recordings and an intersectional viral strategy, we here demonstrate that motor and sensory modulation commands in mice belong to segregated paths within the CST. Sensory modulation is executed exclusively by the CST via a population of lumbar interneurons located in the deep dorsal horn. In contrast, the cortex conveys the motor command via a relay in the upper spinal cord or supraspinal motor centers. At lumbar level, the main role of the CST is thus the modulation of sensory inputs, which is an essential component of the selective tuning of sensory feedback used to ensure well-coordinated and skilled movement.
Highlights
Several brain and spinal structures have been involved in the generation and control of movement, in a task-depending manner
Corticallyevoked primary afferent depolarization (PAD) may inhibit the transmission of sensory information from primary afferents to the central nervous system and can be experimentally assessed by recording dorsal root potentials (DRPs, Fig. 1A)
Our results demonstrate a segregation of pathways involved in cortically-evoked sensory modulation vs. motor control
Summary
Several brain and spinal structures have been involved in the generation and control of movement, in a task-depending manner. PAD can be evoked by the sensorimotor cortex in primates (Abdelmoumene et al, 1970), cats (Andersen et al, 1962; Carpenter et al, 1963; Andersen et al, 1964) and rats (Eguibar et al, 1994; Wall and Lidierth, 1997). These data indicate the cortex can be involved in coordinated movements by modulating sensory afferent fibers via PAD, in addition to the classical drive of motoneurons. We aimed at elucidating the neuronal pathways conveying the cortical motor command and sensory control to the hindlimb in mice
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