Phase coherence of auditory steady-state response reflects the amount of cognitive workload in a modified N-back task

Abstract

The auditory steady-state response (ASSR) is an oscillatory brain activity evoked by repetitive auditory stimuli. Previous studies have reported that the power and phase locking index (PLI) of ASSR could be modulated by the degree of workload. However, those studies used different physical stimuli for tasks of differing difficulty, and the effect of the internal workload itself has not been clearly understood. In this study, we employed the modified N-back task as a visual working memory task in order to vary the degree of difficulty while keeping the physical stimulus constant. The experiment consisted of four types of tasks: No-Load (NL), 1-back, 2-back, and 3-back tasks. The auditory stimulus was a 40 Hz click sound to induce ASSR. Sixteen healthy subjects participated in the present study and magnetoencephalogram responses were recorded using a 148-channel magnetometer system. The hit rate decreased and the reaction time increased according to the task difficulty. Grand averaged phase coherence activities showed the 40 Hz ASSR reductions accompanying an increase in the task difficulty even with the identical external stimuli. In particular, the phase coherence activities in 3-back task were significantly lower than that in the NL and 1-back tasks. Our results suggest that the ASSR can be a useful indicator for the amount of workload in the brain.

Estimation of Human Workload from the Auditory Steady-State Response Recorded via a Wearable Electroencephalography System during Walking

“…The PLI of the ASSR measured by the wearable EEG system significantly decreased as the task difficulty increased. This result is consistent with our previous MEG study (Yokota and Naruse, 2015). Moreover, the PLI was modulated not only according to task difficulty but also the block (experimental order).…”

“…They suggested that the workload related with visual modality has induced desynchronization of 40 Hz ASSR. Previously, we observed a change in the ASSR associated with cognitive load (Yokota and Naruse, 2015). Thus, it appears that the ASSR can be modulated by workload changes in several modalities.…”

“…Several previous studies have successfully used ASSR to define a relationship between workload and task difficulty (Griskova et al, 2007, 2009; Griskova-Bulanova et al, 2011; Roth et al, 2013; Yokota and Naruse, 2015). However, although many studies on EEG measurement during walking have been published, to the best of our knowledge, ours is the first study to estimate workload from the ASSR while participants were walking.…”

“…Previous studies have suggested that the phase-locking index (PLI) of an ASSR can be modulated by changes in workload (Griskova-Bulanova et al, 2011; Yokota and Naruse, 2015). Thus, we focused on the PLI of the ASSR.…”

“…In general, the ASSR is known to be most strongly evoked by a 40 Hz auditory stimulus (Galambos et al, 1981; Ross et al, 2000). Recent studies have shown that the 40 Hz ASSR changes according to the difficulty of a corresponding task (Tiitinen et al, 1993; Griskova et al, 2007, 2009; Griskova-Bulanova et al, 2011; Roth et al, 2013; Yokota and Naruse, 2015). For example, Griskova-Bulanova et al (2011) observed attenuated phase synchronization of the 40-Hz ASSR in a visual search task.…”