Load-dependent activation of bilateral prefrontal cortex: an fNIRS study

Abstract

Objective To investigate the load-dependent activation in bilateral prefrontal cortex (PFC) during working memory tasks by functional near-infrared spectroscopy (fNIRS). Methods Thirty-four undergraduates (17 males and 17 females) completed a standard N-back task at 3 load levels (n=1, 2, 3) while fNIRS data were collected from frontal cortex. Brain activation and relative content of oxygenated hemoglobin (HbO2) in left and right prefrontal cortex was calculated respectively. Results As the load level increased, the accuracy was linearly declined and the action time was significantly prolonged in 1-back than in 2-back and 3-back, but there was no significant difference between 2-back and 3-back. Moreover, the activation of bilateral prefrontal cortex showed non-linear growth with the increase of load level. The activation of bilateral prefrontal cortex in 2-back both presented stronger when compared to 1-back, particularly in the right PFC (P < 0.05). However, there was no obvious difference in the activation of bilateral prefrontal cortex in 3-back when compared to 2-back and 1-back. The time characters of fNIRS showed that the hemodynamic response of the left prefrontal cortex was stronger in 3-back. Conclusion fNIRS could detect the differences in the activation patterns and blood oxygen response mode of bilateral prefrontal cortex under different mental loads. Right prefrontal cortex plays more important role in higher mental load tasks.

Keywords

• functional near-infrared spectroscopy
• mental loads
• brain activation
• prefrontal cortex