Handedness and circadian motor asymmetries in humans: preliminary findings

Previous research studies indicate that a motor activity in the first half of nocturnal sleep is lateralized to the non-dominant hand. It was suggested that such phenomenon may be due to a more pronounced homeostatic deactivation of the dominant hemisphere (referring to the hypothesis of the use-dependent recovery function of sleep). If this were the case we should expect a reversed pattern of motor activity asymmetries between right- and left-handed subjects. We tested this hypothesis in an ecological study assessing the circadian motor activity in seventeen right- and seventeen left-handed subjects. All subjects wore actigraphs on both the left and right wrists for at least twelve consecutive days. In line with previous studies, right-handed subjects showed higher motor activity in the left vs. the right hand in late evening. We did not however find a reverse pattern of results in left-handed participants. On the whole the results do not seem to support the use-dependent recovery hypothesis, and are suggestive of a different circadian phase relationship between the two hemispheres regardless of handedness.