Unlocking Unique Physiological Reactions: Novel Insights into Four Cerebral and Systemic Physiological Responses to...

For several years, our research group has been systematically investigating how changes in cerebral hemodynamics as well as systemic physiology can be induced by colored light exposure (CLE). We have observed that these physiological changes can differ between subjects for exactly the same CLE stimulus. In the present case series, we report specific physiological reactivity patterns from four subjects.

A total of 36 subjects participated in the study. These subjects were exposed to blue and red light while performing a 2-back task. For the present analysis, we selected four subjects as representative examples of distinct response patterns. We simultaneously measured changes in cerebral and systemic physiological parameters using the systemic physiology augmented functional near-infrared spectroscopy (SPA-fNIRS) method. The SPA-fNIRS method included oxygenated hemoglobin ([O₂Hb]) and deoxygenated hemoglobin ([HHb]) in the prefrontal cortex, mean arterial pressure (MAP), end-tidal carbon dioxide (P_ETCO₂), skin conductance level (SCL), and respiration rate (RR).

We identified four distinct patterns of physiological responses. Pattern 1: For all parameters except MAP, the subject's response to blue and red light remained consistent. Pattern 2: Similar to the previous case, there was no significant contrast between red and blue with respect to changes in cerebral hemodynamics. Similar patterns were also detected for P_ETCO₂ and MAP, whereas completely different patterns were found for SCL. Surprisingly, an inverse correlation was found for RR. Pattern 3: Changes in most parameters exhibited mirrored effects. Consistent trends were observed for SCL and RR. Pattern 4: Mirrored patterns were observed for [O₂Hb] and [HHb], the same patterns for P_ETCO₂ and RR, and divergent trends for MAP and SCL.

In our analysis of SPA-fNIRS measurements, we identified four subjects with specific physiological reactivity patterns to a combined CLE and cognitive task. Individual physiological reactivity or physiological constitution should be taken into account when analyzing physiological data on CLE to enable a more adequate interpretation of the results.