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Relaxation from a voluntary contraction is preceded by increased excitability of motor cortical inhibitory circuits.
J Physiol. 2004 Jul 15; 558(Pt 2):685-95.JP

Abstract

Termination of a muscle contraction is as important a part of movement as muscle activation yet the mechanisms responsible are less well understood. In the present experiments we examined the possible role of intracortical inhibitory circuits in terminating a 20% maximum isometric contraction of the first dorsal interosseous muscle (FDI) in eight healthy subjects. Subjects performed the task simultaneously with both hands and received single or pairs (at an interstimulus interval of 3 ms to evaluate short interval intracortical inhibition, SICI) of transcranial magnetic stimuli (TMS) via a focal coil over the motor hand area of the left hemisphere at different times before and after the onset of relaxation. The amplitude of the motor-evoked potential (MEP) following a single or a pair of TMS pulses was measured in the right FDI and plotted relative to the onset of relaxation as estimated from the surface electromyogram (EMG) of the left FDI. MEPs were larger during contraction than after relaxation whereas SICI was absent during contraction and reappeared after relaxation. We found that in all subjects, the time course of MEP changes during relaxation was closely fitted by a Boltzmann sigmoidal curve which allowed us to estimate the mean MEP amplitudes as well as the ratio of the amplitudes after single or pairs of TMS pulses (i.e.%SICI) at any time in the task. The data showed that the amplitude of MEPs to single pulse TMS had started to decline at about the same time as the onset of EMG silence. Furthermore, the size of the MEPs evoked by paired pulses decreased up to 30 ms beforehand. The latter suggests that an increase in SICI occurs prior to the onset of MEP changes, and hence that increased cortical inhibition may play a role in suppressing corticospinal excitability during relaxation. A subsidiary experiment showed that the time relations of changes in SICI and MEP were unchanged by a period of 10 min training on the task.

Authors+Show Affiliations

Sobell Department of Neurophysiology, Institute of Neurology, London, UK.No affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article
Research Support, Non-U.S. Gov't

Language

eng

PubMed ID

15181164

Citation

Buccolieri, Alessandro, et al. "Relaxation From a Voluntary Contraction Is Preceded By Increased Excitability of Motor Cortical Inhibitory Circuits." The Journal of Physiology, vol. 558, no. Pt 2, 2004, pp. 685-95.
Buccolieri A, Abbruzzese G, Rothwell JC. Relaxation from a voluntary contraction is preceded by increased excitability of motor cortical inhibitory circuits. J Physiol. 2004;558(Pt 2):685-95.
Buccolieri, A., Abbruzzese, G., & Rothwell, J. C. (2004). Relaxation from a voluntary contraction is preceded by increased excitability of motor cortical inhibitory circuits. The Journal of Physiology, 558(Pt 2), 685-95.
Buccolieri A, Abbruzzese G, Rothwell JC. Relaxation From a Voluntary Contraction Is Preceded By Increased Excitability of Motor Cortical Inhibitory Circuits. J Physiol. 2004 Jul 15;558(Pt 2):685-95. PubMed PMID: 15181164.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Relaxation from a voluntary contraction is preceded by increased excitability of motor cortical inhibitory circuits. AU - Buccolieri,Alessandro, AU - Abbruzzese,Giovanni, AU - Rothwell,John C, Y1 - 2004/06/04/ PY - 2004/6/8/pubmed PY - 2005/1/26/medline PY - 2004/6/8/entrez SP - 685 EP - 95 JF - The Journal of physiology JO - J Physiol VL - 558 IS - Pt 2 N2 - Termination of a muscle contraction is as important a part of movement as muscle activation yet the mechanisms responsible are less well understood. In the present experiments we examined the possible role of intracortical inhibitory circuits in terminating a 20% maximum isometric contraction of the first dorsal interosseous muscle (FDI) in eight healthy subjects. Subjects performed the task simultaneously with both hands and received single or pairs (at an interstimulus interval of 3 ms to evaluate short interval intracortical inhibition, SICI) of transcranial magnetic stimuli (TMS) via a focal coil over the motor hand area of the left hemisphere at different times before and after the onset of relaxation. The amplitude of the motor-evoked potential (MEP) following a single or a pair of TMS pulses was measured in the right FDI and plotted relative to the onset of relaxation as estimated from the surface electromyogram (EMG) of the left FDI. MEPs were larger during contraction than after relaxation whereas SICI was absent during contraction and reappeared after relaxation. We found that in all subjects, the time course of MEP changes during relaxation was closely fitted by a Boltzmann sigmoidal curve which allowed us to estimate the mean MEP amplitudes as well as the ratio of the amplitudes after single or pairs of TMS pulses (i.e.%SICI) at any time in the task. The data showed that the amplitude of MEPs to single pulse TMS had started to decline at about the same time as the onset of EMG silence. Furthermore, the size of the MEPs evoked by paired pulses decreased up to 30 ms beforehand. The latter suggests that an increase in SICI occurs prior to the onset of MEP changes, and hence that increased cortical inhibition may play a role in suppressing corticospinal excitability during relaxation. A subsidiary experiment showed that the time relations of changes in SICI and MEP were unchanged by a period of 10 min training on the task. SN - 0022-3751 UR - https://www.unboundmedicine.com/medline/citation/15181164/Relaxation_from_a_voluntary_contraction_is_preceded_by_increased_excitability_of_motor_cortical_inhibitory_circuits_ L2 - https://doi.org/10.1113/jphysiol.2004.064774 DB - PRIME DP - Unbound Medicine ER -