The aims of this study were (1) to examine the consistency of the control condition using a test-retest procedure and (2) to more closely examine the hemodynamic variations as a function of task complexity and their relationships with subjective and behavioral data.
Nineteen young adults [18-22 years] performed a working memory task (n-back) with three levels of complexity (1, 2, 3-back) and a control task before (0-back1) and after (0-back2) these three levels of complexity. During each condition, an eight-channel continuous-wave fNIRS device (Oxymon MkIII-Artinis) continuously measured concentrations changes of [HbO2] and [HHb] in the right and left lateral prefrontal cortices (PFC). Behavioral performance was assessed by response time (RT in ms) and response accuracy and subjective perceived difficulty was assessed by the DP-15 [1].
The findings of the present study showed that participants improved their behavioral performance from 0-back1 to 0-back2, although their [HbO2] decreased significantly in both PFC hemispheres. Furthermore, as shown by Molteni et al. [2], participants’ behavioral performance significantly decreased as a function of task-complexity. As regards to the hemodynamic data, the results showed complex activation patterns. But overall, activation in PFC increased as function of complexity. Our results highlight the importance of stabilizing both behavioral performance and hemodynamic variations in the control condition to ensure correct comparisons with the experimental conditions. They also show the interest of using fNIRS to discriminate the activation of the PFC as a function of cognitive load.