Significant activation of the prefrontal cortex is only detected during the mentally more demanding task with fNIRS.

NVC responses were assessed during cognitive n-back stimulation using the functional near-infrared spectroscopy (fNIRS) methodology. Tasks were administered in the following order: 0-back→ 1-back→ 0-back→ 2-back, 0-back being the reference condition, 1-back and 2-back being the tasks with different cognitive demand. Blue dots represent detectors and red dots represent light sources of the fNIRS probe. The 3D probe structure and statistically significant different hemodynamic responses were then projected into the international 10–20 space. t–values are plotted in a color-coded manner to show differences. We observed a statistically significant increase in the oxy-hemoglobin (HbO) levels in the prefrontal cortex (PFC), an increase in the left dorsolateral prefrontal cortex (DLPFC), and a focal increase over the left motor cortex. Data were analyzed using the Brain AnalyzIR software, and a mask was applied on results to only map channels where p_FDR<0.05. t-statistic heatmaps show the significant difference between the more mentally demanding task [2-back] and the less demanding task [1-back] (Panel A). No significant neurovascular coupling response was detected when comparing the [1-back] condition to the baseline condition [0-back] (Panel B). Panel C demonstrates a significant activation during 2-back task when compared to the preceding 0-back task.