[Speaker]

Dr. Kazuhiko Seki
Director
Department of Neurophysiology
National Institute of Neuroscience, National Center of Neurology and Psychiatry

[Abstract]

Skilled hand movements, a key evolutionary advancement in primates, require precise control of muscle activity. This control is mediated by two phylogenetically distinct corticospinal pathways: the "newer" direct corticomotoneuronal (CM) pathways and the "older" indirect pathways involving spinal premotor interneurons (PreM-INs). Despite their critical roles, the functional distinctions between these pathways remain poorly understood. Our experiments in behaving non-human primates reveal that CM cells enable the fine-tuning of individual finger muscles, while PreM-INs coordinate synergistic muscle groups to drive gross motor activity. Additionally, gross muscle activity is automatically regulated by adjusting the gain of the spinal reflex loop involving PreM-INs, which function as a closed positive feedback system. Preliminary findings further suggest that somatosensory gain control during hand movements may also be achieved through a similar dual regulation via direct and indirect sensory ascending pathways.