Right-Left Asymmetry of Prefrontal Cerebral Oxygenation: Does it Depend on Systemic Physiological Activity, Absolute...

We have repeatedly observed a right-left asymmetry (RLA) of prefrontal cerebral oxygenation of subjects during the resting state.

To clarify if the RLA is a reliably observable phenomenon at the group level and whether it is associated with systemic physiology, absolute tissue oxygen saturation (StO₂) or total hemoglobin concentration ([tHb]).

StO₂ and [tHb] values at the right and left prefrontal cortex (PFC) were calculated for two 5- min resting phases based on data from 76 single measurements (24 healthy adults, aged 22.0 ± 6.4 years). StO₂ and [tHb] were measured with an ISS OxiplexTS frequency domain near-infrared spectroscopy device. In addition, end-tidal CO₂ (P_ETCO₂), heart rate (HR), respiration rate (RR) and the pulse-respiration quotient (PRQ = HR/RR) were measured and analyzed for the two phases.

On the group level it was found that i) StO₂ was higher at the right compared to the left PFC (for both phases), ii) RLA of StO₂ (∆StO₂ = StO₂ (right)-StO₂ (left) was independent of P_ETCO₂, HR and PRQ, and iii) ∆StO₂ was associated with absolute StO₂ and [tHb] values (positively and negatively, respectively).

This study shows that i) RLA of StO₂ at the PFC is a real phenomenon, and that ii) ∆StO₂ at the group level does not depend on P_ETCO₂, HR, RR or PRQ, but on absolute StO₂ and [tHb]. We conclude that the RLA is a real effect, independent of systemic physiology, and most likely reflects genuine properties of the brain, i.e. different activity states of the two hemispheres.