Neuroscience Letters 436 (2008) 189–192 Contents lists available at ScienceDirect Neuroscience Letters j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / n e u l e t Effects of chewing in working memory processing Yoshiyuki Hirano a,b,c,d,∗ , Takayuki Obata a , Kenichi Kashikura a,e , Hiroi Nonaka a , Atsumichi Tachibana b,c , Hiroo Ikehira a , Minoru Onozuka b,c a Department of Biophysics, Molecular Imaging Center, National Institute of Radiological Sciences, Chiba, Japan b Department of Physiology and Neuroscience, Kanagawa Dental College, Yokosuka, Japan c Research Center of Brain and Oral Science, Kanagawa Dental College, Yokosuka, Japan d Department of Morphological Neuroscience, Gifu University Graduate School of Medicine, Gifu, Japan e School of Radiological Technology, Gunma Prefectural College of Health Sciences, Maebashi, Japan a r t i c l e i n f o Article history: Received 18 January 2008 Received in revised form 6 March 2008 Accepted 7 March 2008 Keywords: Chewing Working memory Dorsolateral prefrontal cortex fMRI a b s t r a c t It has been generally suggested that chewing produces an enhancing effect on cognitive performance- related aspects of memory by the test battery. Furthermore,recent studies have shown that chewing is associated with activation of various brain regions, including the prefrontal cortex.However,little is known about the relation between cognitive performances affected by chewing and the neuronal activity in specified regions in the brain. We therefore examined the effects of chewing on neuronal activities in the brain during a working memory task using fMRI. The subjects chewed gum, without odor and taste com- ponents, between continuously performed two- or three-back ( n-back) working memory tasks. Chewing increased the BOLD signals in the middle frontal gyrus (Brodmann’s areas 9 and 46) in the dorsolateral prefrontal cortex during the n-back tasks. Furthermore,there were more prominent activations in the right premotor cortex,precuneus,thalamus,hippocampus and inferior parietal lobe during the n-back tasks after the chewing trial. These results suggest that chewing may accelerate or recover the process of working memory besides inducing improvement in the arousal level by the chewing motion. © 2008 Elsevier Ireland Ltd. All rights reserved. It was recently reported that chewing produces an enhancing effect on cognitive performances.Using tests of immediate and delayed recall of words,Wilkinson et al. showed that gum chew- ing could lead to improved performance [30]. In addition, gum chewing appeared to improve both spatial and numeric working memory. Baker et al. reported that gum chewing during encoding a word list improved their recall performance.Moreover, follow- ing gum chewing, memory functions appeared to be enhanced via context-dependent effects [3]. It was also noted that gum chewing appeared to be of benefit to verbal working memory,immediate episodic long-term memory, language-based attention and pro- cessing speed [22]. However, the processes underlying these chewing effects were not elucidated. Tucha et al. reported that sustained attention improved by the chewing of gum affects cognitive performance because chewing affects a specific aspect of attention [29]. Baker et al. argued that, following gum chewing, memory functions appeared to be enhanced via context-dependent effects [3]. Stephens and Tunney reported that gum chewing leads to cogni- ∗ Corresponding author at: Department of Biophysics, Molecular Imaging Center, National Institute of Radiological Sciences, 4-9-1 Anagawa, Chiba 263-8555, Japan. Tel.: +81 43 206 4716; fax: +81 43 206 4079. E-mail address: hirano@nirs.go.jp (Y. Hirano). tive benefits through improved delivery of glucose to the brain, but that some other mechanism is more likely to underlie the facilita- tory effect of gum chewing on delayed episodic long-term memory [22]. Thus, the relation between cognitive performances affected by chewing remains unclear, and besides that, little is actually known about this relation of neuronal activity in specified regions in the brain. Recently,fMRI has become a useful tool for the estimation of chewing effects [21,23,24],whereby it has been reported that chewing activates various regions including the prefrontal cortex [17]. We therefore examined the influence of chewing on neuronal activities in the brain during a working memory task using fMRI. Thirty-three right-handed healthy volunteers (aged 20–39) were enrolled in this study. Two subjects were excluded from the analysis due to motion artifact (>0.75 mm in any direction). There- fore, the data obtained from the remaining 18 subjects (12 males, mean age ± S.E.;24.5 ± 1.0 years) for the two-back task and 13 subjects (8 males, 24.8 ± 1.5 years) for the three-back task were used for the analysis. Written informed consent was obtained from each subject. Experiments were performed according to the ethical guidelines approved by the Committee of the National Institute of Radiological Sciences. We prepared two- and three-back (n-back) tasks with different loads for the working memory task (Fig. 1A) [6]. For the n-back task, subjects were presented a continuous stream of 15 single letters 0304-3940/$ – see front matter © 2008 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.neulet.2008.03.033