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This Article Full Text Full Text (PDF) All Versions of this Article: 99/5/2232    most recent 01273.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Farina, D. Articles by Enoka, R. M. PubMed PubMed Citation Articles by Farina, D. Articles by Enoka, R. M.

Discharge Variability of Motor Units in an Intrinsic Muscle of Transplanted Hand

¹Department of Health Science and Technology, Center for Sensory–Motor Interaction, Aalborg University, Aalborg, Denmark; ²Laboratorio di Ingegneria del Sistema Neuromuscolare, Dipartimento di Elettronica, Politecnico di Torino, Torino, Italy; ³Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden; ⁴Italian Institute of Hand Surgery, Monza, Italy; and ⁵Department of Integrative Physiology, University of Colorado at Boulder, Boulder, Colorado

Submitted 20 November 2007; accepted in final form 27 February 2008

The study analyzed the discharge characteristics of the motor units in an intrinsic muscle of a transplanted hand. Multichannel electromyographic (EMG) recordings were obtained in 11 experimental sessions over 16 mo starting from day 205 after a hand was transplanted in a 35-yr-old man who had lost his right hand 22 yr earlier. The action potentials discharged by single motor units were identified from the surface EMG signals of the abductor digiti minimi muscle in the transplanted hand as the individual performed 60-s maximal and linearly increasing (ramp) contractions. Discharge rate decreased from 27.1 ± 8.4 pulses per second (pps) at the start of the maximal contractions to 17.2 ± 2.9 pps at the end (P < 0.001) and increased from 17.4 ± 4.3 to 22.1 ± 5.0 pps during the ramp contractions (P < 0.05). The SD of the interspike interval (ISI) nearly related to the mean ISI with a similar regression slope for the maximal (0.49 ± 0.09) and ramp contractions (0.43 ± 0.10). The coefficient of variation for ISI was higher than values in able-bodied persons and did not change during either the maximal (36.8 ± 10.8%) or the ramp contractions (35.9 ± 7.4%). High-frequency bursts of activity with <20 ms between two and six action potentials occurred during both maximal and ramp contractions. In conclusion, motor neurons that reinnervated a muscle in a transplanted hand discharged action potentials with a high degree of variability that suggested greater synaptic noise during the voluntary contractions.