Prefrontal cortical response to verbal-spatial two-dimensional task measured by functional NIRS

Abstract

Previous PET and functional MRI studies of working memory (WM) have suggested that prefrontal cortex (PFC) helps WM processes. However, there is controversy on the roles that different PFC regions play in information processes of different materials. Here, we reported a functional near-infrared spectroscopy (NIRS) study on the PFC activation caused by a two-dimensional (verbal versus spatial) n-back task. During the task being performed, concentration changes of oxy-Hb (HbO2), deoxy-Hb (Hb), and total-Hb (HbT) in subjects' prefrontal cortex, which being correlated with cerebral activation, were examined by a 24-channel functional NIRS imager. The behavioral performances (accuracy and response time) were recorded simultaneously. Results revealed that as memory load increased, subjects showed poorer behavioral performance as well as monotonously increasing magnitudes of the PFC activations. In addition, we found that when the subject performed the task as verbal material, the left ventrolateral PFC (VLPFC) and the bilateral dorsolateral PFC (DLPFC) were significantly activated, and when the subject performed the task as spatial material, the right VLPFC and the bilateral DLPFC were significantly activated. This result not only further substantiates previous view that cerebral information processing is lateralized to the left for verbal material and to the right for spatial material, not only provides an evidence that some collaboration mechanisms likely exist between bilateral hemispheres.