Lateralized asymmetries in distribution of muscular evoked responses: An evidence of specialized motor control over an intrinsic hand muscle

Lateralized neural control over hand muscles has been associated with anatomical and physiological asymmetries in the central nervous system. Some studies suggested that the dominant cerebral hemisphere exhibit larger cortical representation areas with lower excitability, while others reported higher cortical excitability in dominant side compared to the contralateral, or even could not find any differences. Thus, neurophysiological lateral asymmetries are still controversial. This study aimed to evaluate differences in dominant and non-dominant sides in motor evoked potentials (MEPs) distribution and investigate whether conventional montages and high-density surface electromyography (HD-sEMG) provide reliable measurements of corticospinal excitability. MEPs elicited by transcranial magnetic stimulation (TMS) were recorded from dominant and non-dominant sides of healthy right-handed participants with an electrode grid over the abductor pollicis brevis muscle. MEPs amplitude distribution, amplitude, latency and resting motor threshold (MT) were evaluated. MEPs distribution significantly shifted towards the lateral direction on the dominant side. MT, amplitude, and latency did not reveal any asymmetries in functional cortical excitability. MEPs amplitude and latency were different for conventional montages and HD-sEMG. Our results suggest that laterality asymmetries manifest in both levels of cortical representation and muscle recruitment, possibly leading to a more pronounced abduction movement on dominant hemisphere compared to the non-dominant side in right-handers. Furthermore, the use of HD-sEMG provided additional insights over conventional electrode montages. A better understanding of laterality asymmetries in fine motor control may help to establish specialized treatments in sensory motor disorders patients.