Reliability of transcallosal conduction time measurements at the abductor pollicis brevis

Abstract

Transcallosal conduction time (TCT) can be measured using transcranial magnetic stimulation (TMS) during a submaximal voluntary contraction of a target muscle. By evaluating the time it takes for a potential to move across the corpus callosum (CC), we hope to see changes during phenomena such as cross-education. In the present study, we stimulated the contralateral and ipsilateral primary motor cortices during a 20% maximum voluntary contraction (MVC) of the abductor pollicis brevis (APB) of both hands in apparently healthy adults (n = 10). The motor evoked potential onset latency (MEPOL) that was obtained with the contralateral M1 stimulation was subtracted from the ipsilateral silent period onset latency (iSPOL) that was obtained through ipsilateral stimulation of the M1, which results in an approximate TCT. This was calculated using measurements at the participants' dominant and non-dominant hands and repeated again after more than 48 hours. Reliability measures of between the two visits showed that these measures were not reliable between visits. With further clarification on the definition of silent period onset latency (SPOL), and improvements in manual measuring techniques, we hope that measuring TCT can be a more accessible way to evaluate changes in interhemispheric interactions.