title: Spinal premotor interneurons mediate dynamic and static motor commands for precision grip in monkeys.
abstract: The extent of spinal interneuron (IN) contribution to dexterous hand movements is unclear. Here, we studied the response patterns and force relationships of spinal premotor INs (PreM-INs) in three awake, behaving monkeys performing a precision grip task. We recorded activity from the cervical spinal cord (C5-T1) simultaneously with electromyographic (EMG) activity from hand and arm muscles during the task. Spike-triggered averaging of EMGs showed that 25 PreM-INs had postspike effects on EMG activity. Most PreM-INs (23/25) displayed movement-related firing rate modulations: 11 had phasic followed by tonic facilitation (p+t+); 4 were pure phasic; 4 were pure tonic; and 4 were deactivated, while their target muscles consistently had p+t+ activity (65/66 muscles). PreM-IN phasic activity started earlier than target muscle activity (49 ± 81.4 ms, mean ± SD), and the peak amplitude was correlated with the peak amplitude of the rate of change of grip force (4/17, p < 0.05), suggesting that they contributed to force initiation. In contrast, PreM-IN tonic activity started at almost the same time as the target muscle activity and the mean firing rate was correlated with the mean grip force during the hold period (4/15, p < 0.05), suggesting that they contributed to force maintenance. These results indicated that the neural pathway mediated by the spinal PreM-INs makes a significant contribution to the control of precision grip in primates.
authors.affiliation: Department of Neurophysiology, National Institute of Neuroscience, Tokyo 187-8502, Japan.
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Takei
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Seki
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D004576:Electromyography; D006225:Hand / Q000502:physiology; D018737:Hand Strength / Q000502:physiology*; D007395:Interneurons / Q000502:physiology*; D008252:Macaca fascicularis; D008253:Macaca mulatta; D008297:Male; D009046:Motor Neurons / Q000502:physiology; D009068:Movement / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D011930:Reaction Time / Q000502:physiology; D013116:Spinal Cord / Q000166:cytology*; D013223:Statistics as Topic