Characterization of corticospinal activation of finger motor neurons during precision and power grip in humans

• Published in: Experimental brain research Vol. 236; no. 3; pp. 745 - 753
• Main Authors: Svane, Christian, Forman, Christian Riis, Nielsen, Jens Bo, Geertsen, Svend Sparre
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.03.2018; Springer; Springer Nature B.V
• Subjects: Adult; Biomedical and Life Sciences; Biomedicine; Correlation analysis; Electromyography; Evoked Potentials, Motor - physiology; Female; Fingers; Fingers - physiology; Grasping; Hand Strength - physiology; Humans; Magnetic fields; Male; Motor neurons; Motor Neurons - physiology; Motor units; Movement (Physiology); Muscle, Skeletal - physiology; Muscles; Neurology; Neurosciences; Observations; Physiological aspects; Pyramidal tracts; Pyramidal Tracts - physiology; Research Article; Synchronization; Transcranial magnetic stimulation; Transcranial Magnetic Stimulation - methods; Young Adult; PSTH; Pinch; Corticomotoneuronal cells; Synchronization; Grasp; Coherence
• ISSN: 0014-4819; 1432-1106; 1432-1106
• DOI: 10.1007/s00221-018-5171-0

Direct and indirect corticospinal pathways to finger muscles may play a different role in control of the upper extremity. We used transcranial magnetic stimulation (TMS) and coherence analysis to characterize the corticospinal drive to the first dorsal interosseous (FDI) and abductor pollicis brevis (APB) when active during a precision and power grip task. In experiment 1, single motor units were recorded during precision grip and power grip in 20 adults (25.2 ± 7.1 years). Post-stimulus time histograms (PSTH) were obtained following TMS. In experiment 2, coherence and cross-correlation analysis of the FDI and APB surface EMG were used to investigate the temporal organization of corticospinal drive during precision grip and power grip in 15 adults (27.4 ± 8.1 years). We found no significant differences in PSTH peak onset (26.6 ± 1.9 vs. 26.7 ± 2.0 ms, p  = 0.75), maximal peak (27.4 ± 1.9 vs. 27.4 ± 1.9 ms, p  = 1.0) or peak duration (2.3 ± 1.1 vs. 2.3 ± 1.0 ms, p  = 0.75) for the 11 recovered motor units during precision grip and power grip. Also, no significant difference in coherence or the width of the synchronization peaks during precision grip (7.2 ± 3.7 ms) and power grip (7.9 ± 3.1 ms) could be observed ( p  = 0.59). The short duration of peaks elicited in the PSTH of single motor units following TMS and central synchronization peaks of voluntarily activated motor units during precision and power grip suggests that the direct corticospinal pathway (the corticomotoneuronal system) is equally involved in the control of both tasks. The data do not support that indirect pathways would make a larger contribution to power grip.