Circadian motor asymmetries in humans

Previous research studies indicate that motor activity during sleep is lateralized to the non-dominant hand. We put forward the hypothesis that the relative superiority of the non-dominant hand movements during night could arise from a different circadian phase relationship between the two hemispheres, independently of the sleep condition. The present study evaluated whether actigraphic data are consistent with such hypothesis. A total of 58 right-handed university students wore actigraphs (AMI 32K) on both left and right wrist for 3 consecutive days. Mesor and acrophase were computed using cosinor analysis. Moreover, factorial analysis of variances were carried out on side (left versus right) and time of day. The results indicated that the left hand circadian rhythm had a significant phase delay in comparison to the right hand one. The mean activity of the left hand was significantly higher than that of the right hand from 20:00 until 04:00 h. The results are suggestive of a different circadian activation between the two hemispheres and are discussed in relation to models of circadian regulation of sleep/wake cycle.