Near Infrared Spectroscopy (NIRS)

Prior to each in situ testing session, participants were fitted with a Portalite NIRS sensor (Portalite, Artinis Medical Solutions, Netherlands), which uses light in the near-infrared spectrum to measure cerebral activation. The Portalite NIRS system consists of three channels, with inter-optode distances of 30, 35, and 40 mm, enabling a penetration depth of 20 mm into the prefrontal cortex. Consistent with previous research, the sensor was positioned approximately one centimeter above the participants’ right eyebrow, to enable measurement of cerebral oxygenation in the right prefrontal cortex, while avoiding sinus cavities and hair that might interfere with the signal (Yoshitani et al., 2002; Helton et al., 2007a). As oxyhemoglobin (O2Hb) and deoxyhemoglobin (HHb) have distinct optical absorption characteristics, NIRS can be used to determine the relative amounts of each in the cerebral tissue. The ratio of O2Hb to total hemoglobin (O2Hb + HHb) is used to calculate regional oxygen saturation (rSO2), which can be used as a measure of cerebral activation (Ekkekakis, 2009).

The baseline period was 2 min prior to each testing session, during which time participants were asked to sit quietly, minimize body movements and to remain as relaxed as possible. rSO2 during the second minute of the baseline period was used as a baseline index. rSO2 scores for each of the four, 5-min work periods were calculated by comparing mean rSO2 during each period of the in situ testing to the baseline rSO2 measure. Scores represent the percentage change in rSO2 from baseline, with positive scores representing an increase in rSO2 compared to baseline, and negative scores represented a decrease in rSO2 compared to baseline.