Frontal Electroencephalogram Alpha Asymmetry during Mental Stress Related to Workplace Noise

Abstract

This study aims to investigate the effects of workplace noise on neural activity and alpha asymmetries of the prefrontal cortex (PFC) during mental stress conditions. Workplace noise exposure is a pervasive environmental pollutant and is negatively linked to cognitive effects and selective attention. Generally, the stress theory is assumed to underlie the impact of noise on health. Evidence for the impacts of workplace noise on mental stress is lacking. Fifteen healthy volunteer subjects performed the Montreal imaging stress task in quiet and noisy workplaces while their brain activity was recorded using electroencephalography. The salivary alpha-amylase (sAA) was measured before and immediately after each tested workplace to evaluate the stress level. The results showed a decrease in alpha rhythms, or an increase in cortical activity, of the PFC for all participants at the noisy workplace. Further analysis of alpha asymmetry revealed a greater significant relative right frontal activation of the noisy workplace group at electrode pairs F4-F3 but not F8-F7. Furthermore, a significant increase in sAA activity was observed in all participants at the noisy workplace, demonstrating the presence of stress. The findings provide critical information on the effects of workplace noise-related stress that might be neglected during mental stress evaluations.

Keywords: EEG alpha-asymmetry; electroencephalogram (EEG); noise stress; prefrontal cortex; salivary alpha-amylase.

Figure 1

Timeline of the experimental protocol (B = baseline, α = alpha-amylase, MAT = mental arithmetic task).

Figure 2

Sixteen EEG selected channels were arranged above the prefrontal cortex (PFC).

Figure 3

Mean activity of salivary alpha-amylase for stress and baseline at quiet and noisy workplaces. The error bars indicate the standard deviations and the stars indicate the significant differences (*** p < 0.001).

Figure 4

Percent performance in the MIST under stress conditions at quiet and noisy workplaces. Error bars indicate the standard deviations and stars (**) indicate significant differences ** p < 0.01.

Figure 5

Average absolute alpha power for each subject while working at quiet and noisy workplaces.

Figure 6

(a) Mean of frontal alpha asymmetry scores obtained during the quiet and noisy workplaces. Error bars indicate the standard deviations; (b) Topographical maps of alpha power for each workplace. Note: the alpha power is inversely associated with cortical activation. The asterisk (*) indicates p < 0.05.

Figure 7

Average natural log alpha power recorded from the right frontal (F4 and F8) and left (F3 and F7) at quiet and noisy workplaces. Error bars indicate the standard deviation, and stars (***) signify significant differences *** p < 0.001.