Reticulospinal involvement in force production depends on effector and degree of force modulation


The nervous system executes movements primarily through the corticospinal and reticulospinal descending tracts. Although it was previously thought that the reticulospinal tracts are predominantly used for locomotion and postural adjustments, recent evidence implicates reticulospinal involvement in voluntary movements, although in differing degrees depending on the type of movement and muscles involved. The purpose of the current study was to assess the relative degree of reticulospinal contributions to various movements executed using wrist flexors versus wrist extensors. Participants performed a bimanual force production task that required either wrist flexion, wrist extension, or wrist flexion with one arm and wrist extension with the other arm. In addition to the use of different effectors, participants either produced a constant force or were required to track an oscillating force target to assess how force modulation affected the pathways involved in movement control. Neural contributions were assessed using EMG-EMG coherence, which quantifies the relative degree of common drive to both muscles in the frequency domain. During the constant force task, results showed increased 8-20 Hz coherence for bimanual flexion movements compared to all other conditions, indicative of greater reticulospinal drive. Additionally, increased coherence in the 8-12 Hz (alpha) band was found for force tracking as compared to constant force for all movement types, which may represent continuous monitoring of force feedback and tracking error. Overall, these findings provide evidence that brainstem structures contribute to force production differentially depending on involved effectors and may be implicated in force control and error prediction.

Acknowledgments: This research was supported by the Natural Sciences and Engineering Research Council of Canada and the Ontario Ministry of Research, Innovation and Science.