Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
4327145 | Brain Research | 2010 | 13 Pages |
Abstract
In this experiment, the changes in excitability of motor axons produced after natural activity were measured in nine healthy subjects using 1 min of maximal voluntary contractions (MVC) of the abductor digiti minimi (ADM) by studying the relationship between stimulus intensity applied to the ulnar nerve and the size of the ADM compound muscle action potential (CMAP). On cessation of the contraction, there was a prominent right-shift of the input-output curve: the intensity required to produce a control CMAP â¼Â 60% of maximum, generated a post-contraction response â¼25% of maximum. Similar changes occurred in the input-output curves obtained by recording the ulnar nerve volley evoked by same test stimulus for CMAP. Motor-evoked potential (MEP) and F-waves (and H-reflex in one subject) were recorded from ADM before and after 1 min of MVC. On cessation of contraction, the MEP input-output curves exhibited a significant right-shift: the stimulus required to evoke a pre-contraction maximum MEP (â¼60% of maximum CMAP) generated a post-contraction response â¼Â 65% of initial values. One minute of MVC produced similar decreases of F (â¼Â 35%)- and H (â¼Â 30%)-ADM responses. All responses recovered their control value in 15-20 min after the end of contraction. The almost identical depressive effect produced by 1 min of MVC on peripherally and centrally generated muscle responses suggests a common conditioning factor. These findings are discussed within the context of activity-induced motor axonal hyperpolarizion.
Keywords
MEPTMSCNAPCMAPADMMVCRMSelectromyographyEMGstandard deviationTranscranial magnetic stimulationMotoneuron excitabilityCsApmaximal voluntary contractionstandard errorAbductor Digiti MinimiVoluntary activityMotor evoked potentialroot mean squarecompound nerve action potentialcompound muscle action potential
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Authors
Alessandro Rossi, Alessia Biasella, Cristiano Scarselli, Pietro Piu, Federica Ginanneschi,