Fig. 4

Effect of irradiance level of light on brain responses of younger and older individuals performing an auditory two-back task. Statistical results (p < 0.001 uncorrected) overlaid over the mean structural image of all participants. Significant changes in responses as a function of irradiance level are displayed in yellow for younger individuals (Y) and in red for older individuals (O), whereas group differences (Y > O) are in blue. Panels a–e represent estimates [a.u. ± standard error of the mean (SEM)] of the brain responses while exposed to blue light independent of the irradiance change. Panels f–j represent estimates (a.u. ± SEM) of the linear change in brain responses with change in irradiance level. Panels k–o consist of a schematic representation of the composite of both components (responses to light and irradiance change) showing the evolution of the responses with change in irradiance level. Panels m–o only includes younger  individuals because responses were not significantly affected by irradiance change in older individuals in the brain regions considered. *Significantly activated, p < 0.05 corrected for multiple comparisons over small volumes of interest; ^#significant group differences, p < 0.05 corrected for multiple comparisons over small volumes of interest; n.s. non significant group difference. Abbreviations: a & f CALC calcarine sulcus, b, e, g, & j IOG/MOG/SOG inferior/middle/superior occipital gyrus, c & h FPC frontopolar cortex, d & i CEREB cerebellum. Please refer to Table 3 of [113] for brain clusters coordinates. Reproduced with permission from [117]