The objective of this study was to examine the association between sleep bruxism and psychological stress. The subjects consisted of 76 volunteers, who were divided into those with and without bruxism according to the diagnostic criteria for sleep bruxism outlined by the American Academy of Sleep Medicine (AASM). Stress sensitivity was evaluated before and after an experimental stress task, which involved simple mathematical calculations. It was assessed objectively by measuring the subjects' salivary chromogranin A (CgA) levels and subjectively using a ten-division visual analog scale (VAS). Compared with those observed before the stress task, the mean salivary CgA levels of the non-bruxism group (n = 54) were not significantly increased after the stress task. Conversely, the mean salivary CgA levels of the bruxism group (n = 22) were significantly increased after the stress task (P < 0.01). The mean VAS scores of the groups without (n = 54) and with (n = 22) bruxism were significantly (P < 0.01) increased after the stress task compared with those observed before the stress task, but no differences were detected between the two groups in the stress task. These findings suggest that there is an association between sleep bruxism and psychological stress sensitivity.Oral habits such as bruxism are thought to affect temporomandibular disorders (TMD) and might have a relatively strong effect on the durability of prosthetic appliances (20,30). Bruxism, which is defined as clenching or grinding of the teeth, or a combination of both, is a diurnal or nocturnal parafunctional activity and has long been regarded as requiring treatment (5). It is thought that bruxism is associated with psychological stress (1,2,8,10,22). On the other hand, some studies did not find any association between bruxism and stress (15,19). The following reasons might explain this disagreement. In most of the above studies, diurnal bruxism and sleep bruxism were not distinguished from each other, and there were variations in the methods used to evaluate oral habits. In addition, differing definitions of stress and various methods for assessing stress were employed in these studies (17). Also, in these studies, stress was evaluated subjectively, such as by self-reporting, questionnaires, etc. Thus, the relationship between bruxism and stress is much more complex than previously imagined and involves many psychosocial factors (17). When humans are exposed to psychological stressors, the hypothalamic-pituitary-adrenal (HPA) axis and the sympathoadrenal medullary (SAM) system are activated (9,13,26). This results in changes of biomarkers, e.g., cortisol and/or chromogranin, etc., being secreted into the serum or saliva. Therefore, stress can be objectively evaluated by analyz-

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Intertidal fishes have elaborated spatial cognitive abilities. In this study, we developed an appetitive conditioning paradigm for an intertidal fish species (the chameleon goby; Tridentiger trigonocephalus) that involves spatial components and ethologically relevant cue stimuli. The gobies rapidly acquired the conditioned anticipatory behaviour after only a few trials of paired presentations of virtual tidal changes and food rewards (which were only available in specific locations during a simulated high tide). The conditioned responses were retained after exposure to a 1 month period without trainings or tidal changes. The rapid acquisition and long-term retention of the conditioned responses indicates that the learning paradigm, which used a combination of water level changes and food availability in specific spatial locations, is biologically significant for this species. Taken together, these results suggest that spatial tasks combined with virtual tidal changes provide a suitable paradigm for evaluating spatial cognitive mechanisms in intertidal fishes.