Frontal cortex activation associated with speeded processing of visuospatial working memory revealed by multichannel near-infrared spectroscopy during Advanced Trail Making Test performance

Although visuospatial working memory (VSWM) is commonly used during speeded and unconscious memory processing in daily life, most neuroimaging studies on VSWM use tasks that impose motor restrictions onto the examinees to avoid movement-related artifacts. Multichannel near-infrared spectroscopy (NIRS), however, can measure cortical activation during cognitive processing without interfering with task procedure. The purpose of this study is to determine whether multichannel NIRS can detect VSWM-induced frontal cortex activation similar to that seen in VSWM performance in daily-life activity. Using NIRS, we measured relative changes in the concentration of oxygenated hemoglobin as an index of frontal activation in 52 measurement points (channels) on the frontal area during the Advanced Trail Making Test (ATMT), a tool used to assess VSWM. The ATMT consists of two tasks, R and F, with the former assessing motor factors and the latter relating to both motor and cognitive factors involved in speeded and unconscious VSWM operations. Twenty-six healthy volunteers were enrolled in this study. Channel activation during Task F performance was observed bilaterally over the dorsolateral and ventrolateral prefrontal cortex. This distribution may reflect central executive function of working memory. Channel activation during Task R was circumscribed to part of the left ventrolateral prefrontal cortex partially overlapping with areas active during Task F performance, likely representing task-related motor factor activation. Our findings suggest that multichannel NIRS during ATMT performance is an appropriate means of measuring cortical activation induced by VSWM operations during daily activity.