FRONTAL MIDLINE THETA RHYTHM: COMMENT ON CHAN AND HSU (2010)

Summary.—That the frontal θ rhythm of EEGs increases in magnitude during various mental tasks which require focusing of attention is well-known. The task includes visual-search tasks using a visual display terminal (VDT) and Chinese characters. The purpose of the experiment by Chan and Hsu (2010) was to investigate whether working memory is reduced in a task using a visual display terminal (VDT). The authors examined behavioral performance and EEG changes associated with memory load in a visual-search task using a VDT. Performance decreased as task difficulty increased, which is con sistent with many previous reports. This finding suggests a disadvantage for the VDT task. On the other hand, the EEG analysis showed no signifi cant changes in θ and α bands with altered task difficulty. Although such results might suggest dissociation between memory load and EEG change in the VDT task, these findings were not consistent with previous reports (Gevins, Smith, McEvoy, & Yu, 1997; Onton, Delorme, & Makeig, 2005). Numerous studies have explored the effects of memory load on EEGs. Ishihara and Yoshii (1972) studied extensively θ waves recorded from the frontal areas during wakefulness. They described the θ waves in the frontal areas during mental tasks and termed them Fm θ (Frontal midline θ) rhythm. Fig. 1a shows a burst of θ waves recorded at the frontal sites during the Uchida-Kraepelin test. The amplitude of the θ waves was higher at Fz than Fp2 or Cz. These θ waves with a peak frequency of 6.6 Hz also appeared during a visual-detection task using the VDT (Figs. 1b, 1c; Sasaki Sakane, Ishida, Todorokihara, Kitamura, & Aoki, 2008). It is important that some experimental factors should be controlled. First, there is a large variability in the appearance of the Fm θ both between participants and between trials. Therefore, selection of participants or their classification is important in analyzing the homogeneous data (Ishihara & Yoshii, 1972; Asada, Fukuda, Tsunoda, Yamaguchi, & Tonoike, 1999). On the other hand, the intertrial variability may suggest that Fm θ relates some contextual factors (Onton, et al., 2005). Second, eye blinks