RIGHT- AND LEFT-BRAIN HEMISPHERE. RHYTHM IN REACTION TIME TO LIGHT SIGNALS IS TASK-LOAD-DEPENDENT: AGE, GENDER, AND HANDGRIP STRENGTH RHYTHM COMPARISONS

Abstract

In healthy mature subjects simple reaction time (SRT) to a single light signal (an easy task) is associated with a prominent rhythm with τ=24 h of dominant (DH) as well as nondominant (NDH) hand performance, while three-choice reaction time (CRT), a complex task, is associated with τ=24 h of the DH but τ<24 h of the NDH. The aims of the study were to assess the influence of age and gender on the difference in τ of the NDH and DH, as it relates to the corresponding cortical hemisphere of the brain, in comparison to the rhythm in handgrip strength. Healthy subjects, 9 (5 M and 4 F) adolescents 10–16 yr of age and 15 (8 M and 7 F) adults 18–67 yr of age, active between 08:00±1 h and 23:00±1:30 h and free of alcohol, tobacco, and drug consumption volunteered. Data were gathered longitudinally at home and work 4–7 times daily for 11–20 d. At each test time the following variables were assessed: grip strength of both hands (Dynamometer: Colin–Gentile, Paris, France); single reaction time to a yellow signal (SRT); and CRT to randomized yellow, red, or green signal series with varying instruction from test to test (Psycholog-24: Biophyderm, France). Rhythms in the performance in SRT, CRT, and handgrip strength of both DH and NDH were explored. The sleep–wake rhythm was assessed by sleep-logs, and in a subset of 14 subjects it was also assessed by wrist actigraphy (Mini-Motionlogger: AMI, Ardsley NY). Exploration of the prominent period τ of time series was achieved by a special power spectra analysis for unequally spaced data. Cosinor analysis was used to quantify the rhythm amplitude A and rhythm-adjusted mean M of the power spectral analysis determined trial τ. A 24h sleep–wake rhythm was detected in almost all cases. In adults, a prominent τ of 24 h characterized the performance of the easy task by both the DH and NDH. In adults a prominent τ of 24 h was also detected in the complex CRT task performed by the DH, but for the NDH the τ was <24 h. This phenomenon was not gender-related but was age-related since it was seldom observed in adolescent subjects. Hand-side differences in the grip strength rhythms in the same individuals were detected, the τ being ultradian rather than circadian in adolescent subjects while in mature subjects the τ frequently differed from that of the rhythm in CRT. These findings further support the hypothesis that functional biological clocks exist in both the left and right hemispheres of the human cortex.

• Age
• Circadian rhythms
• Cortical hemisphere of brain
• Gender
• Handgrip strength
• Reaction time
• Task-loading
• Ultradian rhythms