Multichannel Surface EMGs to Assess Function of Spinal Anterior Horn Cells

Abstract

Peristimulus time histograms (PSTHs) have been constructed from needle electromyographic (nEMG) recordings, and used to evaluate the function of spinal anterior horn cells to inputs from the corticospinal tract or Ia afferents. However, nEMG is a painful and uncomfortable technique, and to overcome these difficulties, we have recorded surface EMGs (sEMGs) from an 8 electrode array with interelectrode distances of 5 mm. With this array, we were able to record motor unit potentials (MUPs) from which the PSTHs can be constructed. The electrode array was aligned with the long axis of the right abductor pollicis brevis while transcranial magnetic stimulation (TMS) was directed to the motor area of the right hand. With a careful control of voluntary muscular contraction, a single MUP could be isolated, and PSTHs could be constructed. Our results show that the properties of these PSTHs were very similar to those constructed from nEMGs. We conclude that multichannel sEMGs can be used to construct PSTHs non-invasively, which then enables us to explore dysfunctions of the pyramidal tract such as in cases of amyotrophic lateral sclerosis.