Relation between working memory performance and evoked cerebral blood oxygenation changes in the prefrontal cortex evaluated by quantitative time-resolved near-infrared spectroscopy.

OBJECTIVES The lateral prefrontal cortex (LPFC) plays a central role in working memory (WM). In the present study, we employed quantitative, near-infrared time-resolved spectroscopy (TRS) to evaluate the relation between LPFC activity during WM and the task performance in 19 healthy, middle-aged, female subjects (mean age of 46·8±2·1 years). METHODS Concentration changes of oxyhemoglobin (oxy-Hb), deoxyhemoglobin, and total hemoglobin in the bilateral LPFC were measured by means of TRS during performance of Sternberg tests (ST) of one digit and six digits. The oxy-Hb changes were compared to performance in ST. In addition, we evaluated whether pathlength of the forehead and baseline concentration of oxy-Hb influenced WM performance. RESULTS TRS revealed increases in oxy-Hb in association with a decrease in deoxy-Hb during ST. We found a significant negative correlation between the reaction time of six-digit ST and oxy-Hb changes in the bilateral LPFC (left, P = 0·0061; right, P = 0·0029); however, no significant correlation was observed with one-digit ST. In contrast, accuracy of ST did not correlate with the oxy-Hb changes in the prefrontal cortex. The optical pathlength of the forehead and concentration of oxy-Hb at rest in the LPFC did not correlate with either reaction time or accuracy in ST. CONCLUSION The present results indicate that oxy-Hb changes in the LPFC during a WM task, as measured by TRS, correlated with WM performance. TRS is compact and less expensive than functional magnetic resonance imaging, and may be a useful tool to evaluate neural correlates of WM in normal adults.