Effects of chewing on cognitive processing speed
Highlights
► Chewing accelerates cognitive processing speed. ► fMRI BOLD response in the anterior cingulate and left frontal gyrus for executive network after chewing. ► Chewing affects motor-related brain regions for attentional network test.
Introduction
Recently, behavioral studies were performed to examine the relationship between chewing and cognitive performance including memory, attention and executive function. With regard to memory, it has been reported that gum chewing improves episodic and working memory during chewing, suggesting at least in part that chewing promotes regional cerebral blood flow and glucose delivery (Stephens and Tunney, 2004, Wilkinson et al., 2002, Zoladz and Raudenbush, 2005). However, the existence of enhanced performance of episodic memory task by context-dependent effects induced by chewing has remained controversial (Baker et al., 2004, Johnson and Miles, 2007, Johnson and Miles, 2008, Stephens and Tunney, 2004). As for attention, it was reported that sustained attention (Smith, 2009a, Smith, 2010, Tucha et al., 2004) and language-based attention (Stephens & Tunney, 2004) were improved by chewing. On the other hand, Tucha et al. (2004) claimed not only that memory functions were not improved but also that tonic and phasic alertness were adversely affected by chewing. With respect to executive function, a study claimed that chewing gum does not appear to be of benefit to word association executive function (Stephens & Tunney, 2004), but another study reported a beneficial effect (Onyper, Carr, Farrar, & Floyd, 2011).
To elucidate these inconsistent results and their mechanisms, several functional neuroimaging studies have been conducted. These studies suggested that chewing facilitated the process of working memory and also that it was related to attention (Hirano et al., 2008, Wang et al., 2009). As well, several studies mentioned that chewing affects arousal (Onyper et al., 2011, Sakamoto et al., 2009, Smith, 2010, Stephens and Tunney, 2004). Sakamoto et al. (2009) studied the effect of chewing on the central nervous system by measuring reaction time (RT) and event-related potentials (ERPs). They suggested that chewing influences the state of arousal via the ascending reticular activating system, and that it accelerates cognitive processing.
Based on these studies, we assumed that chewing also affects aspects of attention and accelerates cognitive processing. Indeed, recent studies, pointing out that reaction times were shortened by chewing in the categoric search task (Allen and Smith, 2012a, Smith, 2010), vigilance task (Allen & Smith, 2012a), language-based attention task (Stephens & Tunney, 2004), and the encoding of new information in the focused attention task (Smith, 2010). Smith (2010) speculated that positive cognitive performance may come from the fact that subjects feel more alert as described, being energetic, quick-witted and attentive, all based on mood improvement. However, some studies reported not only that the performance of sustained attention was not accelerated (Kohler et al., 2006, Smith, 2010, Tucha et al., 2010) but also that vigilance task was decelerated (Tucha et al., 2010). Tucha et al. (2010) indicated that the psychodynamics of gum chewing might be an important factor, and these conflicts of cognitive performance may originate from the duration of the study (Tucha et al., 2010) and time of the task (Allen and Smith, 2012a, Allen and Smith, 2012b, Tucha and Simpson, 2011). Indeed, Tänzer, Von Fintel, and Eikermann (2009) reported that chewing benefit in concentration performance showed up after 14 min from the initiation of the test. To elucidate the mechanism of this issue, we considered that a functional magnetic resonance imaging (fMRI) assessment might be helpful. The attentional network test (ANT) provided a way of testing for the efficiency of the alerting, orienting and executive (conflict resolution) functions of attention (Fan, McCandliss, Sommer, Raz, & Posner, 2002), and it was adapted within a single session of event-related fMRI (Fan, McCandliss, Fossella, Flombaum, & Posner, 2005). In the current study, we examined the effects of chewing on alerting and executive attention and their processing speed by comparing the behavioral and fMRI results of ANT.
Section snippets
Subjects
Nineteen healthy volunteers (aged 20–34) were enrolled for assessment by random-effect analysis (Seghier, Lazeyras, Pegna, Annoni, & Khateb, 2008) in this study. Two participants were excluded from the analysis due to motion (>0.56 mm, corresponding to 15% of voxel size in-plane) during the fMRI scan. Therefore, data from 17 healthy volunteers (mean age ± SD, 25.2 ± 4.79 years; range, 20–34 years; 8 females) were evaluated in this study. Written informed consent was obtained from all subjects. The
Behavioral analysis
Table 1 shows mean RT and accuracy for each condition. Three-way repeated measures ANOVA of RT showed that the main effects of chewing condition (F(1, 16) = 20.30, p < 0.001, effect size = 0.56), target condition (F(1, 16) = 97.29, p < 0.001, effect size = 0.86), and cue condition (F(1, 16) = 9.03, p < 0.01, effect size = 0.36) were significant. The interactions between chewing condition and target condition (F(1, 16) = 0.78, effect size = 0.05), chewing condition and cue condition (F(1, 16) = 0.12, effect size = 0.01),
Discussion
At first, the main effects of ANT were identified in both cue condition (no cue and center cue) and target condition (congruent and incongruent) in this study (Table 1). The results indicate that our version of ANT was valid with even shorter testing time than that in a past study, which we refer to as modified ANT for fMRI (Fan et al., 2005). Also, the behavioral effects (Table 2) and RT were roughly equivalent (alerting effect was 4% longer and mean RT was 13% shorter) except for conflict
Acknowledgments
We would like to thank Dr. Chihiro Sutoh for helpful discussion and Ms. Hiroko Kamada for technical assistance. This work was supported in part by Research Fellowships of the Japan Society for the Promotion of Science for Young Scientists (17-6577) and a Grant-in-Aid for Molecular Imaging Program from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japanese Government.
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