Frontal cerebral oxygenation asymmetry: intersubject variability and dependence on systemic physiology, season, and time of day.

Our study reveals that frontal cerebral oxygenation asymmetry (FCOA), i.e. a difference in the oxygenation between the right and left prefrontal cortex (PFC), is a real phenomenon in healthy human subjects at rest. To investigate FCOA, we performed a study with 134 healthy right-handed subjects with the systemic physiology augmented functional near infrared spectroscopy (SPA-fNIRS) approach. Subjects were measured 2 to 4 times on different days resulting in an unprecedented number of 518 single measurements of the absolute values of tissue oxygen saturation ( ) and total hemoglobin concentration ([tHb]) of the right and left PFC. Measurements were performed with frequency-domain functional near-infrared spectroscopy. In addition, the cardiorespiratory parameters were measured simultaneously. We found that (i) subjects showed an FCOA (higher on the right PFC), but not for tHb; (ii) intrasubject variability was excellent for both and tHb, and fair for FCOA; (iii)  correlated significantly with blood concentration, [tHb] with heart rate, respiration rate (RR), and the pulse-respiration quotient (PRQ), and FCOA with RR and PRQ; (iv) FCOA and were dependent on season and time of day, respectively; (v) FCOA was negatively correlated with the room temperature; and (vi)  and tHb were not correlated with the subjects mood but with their chronotype, whereas FCOA was not dependent on the chronotype. Our study demonstrates that FCOA is real, and it provides unique insights into this remarkable phenomenon.