Circadian rhythm period in reaction time to light signals: difference between right- and left-hand side.

The study was designed to test the hypothesis that the prominent rhythm period tau of simple reaction time (SRT) and three-choice reaction time (CRT) to light signals may vary between the dominant (DH) and non-dominant (NDH) hand. Eleven healthy subjects, 8 males (16-74 years, including two left-handed) and 3 females (18-43 years), synchronized with a diurnal activity (approximately 07.00 h to approximately 23.00 h) and a nocturnal rest, volunteered for the study. A battery-powered ambulatory device was used to self-record SRT to a yellow light signal and CRT to yellow, green and red signals. Tests were performed 4-7 times/24 h during a 12- to 15-day span. Power spectra, ANOVA, cosinor, chi2 and correlation tests were used to individually analyze time series. Tau = 24 h in SRT rhythms of DH (8/11 cases) and NDH (6/11 cases) with chi2 = 3.5 and p > 0.05. In CRT rhythms, tau = 24 h for DH (8/11 cases) while tau = 8 h for NDH (7/11 cases), a difference which was statistically significant (chi2 = 9.4 with p < 0.02). Concordant results were obtained with other statistical tests leading to the conclusion that the rather complex cognitive task (CRT) and, to a certain extent, SRT of certain individuals, were associated with tau = 24 h for DH and tau = 8 h for NDH. These findings are in favor of the hypothesis that functional clocks are present in the human brain cortex, associated with the possible expression of rhythms with a prominent period differing from the right- and left-hand side.