Functional relevance of the precuneus in verbal politeness
Introduction
Hierarchy is universal in social species, and organizes inter-individual interactions and communication. Social cognition of dominance and ranking has been observed in species of primates (Bergman et al., 2003), birds (Paz-y-Mino et al., 2004), fish (Grosenick et al., 2007), and ants (Blacher et al., 2010, Xu and Chen, 2010). In primates, the relevance of social hierarchy is not confined to agonistic and sexual competition. Ritualized submission cues from losers can elicit social reconciliation in potentially aggressive encounters, reinforcing the social hierarchy (de Waal, 1986). This kind of social behaviors observed in animals might be similar to human “politeness” (Brown and Levinson, 1987). However, the influence of human “politeness” is complex and sophisticated in comparison with social behaviors of animals and ranges from everyday social etiquette to formal diplomatic protocols. Politeness can be defined as a behavior that is respectful and considerate of other people. Politeness is thus not merely the social cognition of dominance, but rather social behavior that often relates to hierarchy. This context-dependent behavior modification might require self-referential cognition of social hierarchy. Politeness can be expressed in both verbal and non-verbal way. For example, the respect to the other person can be represented in special dress codes, facial expressions, gestures or bodily postures.
Regarding the verbal politeness, its formal manifestation is honorific language (verbally-expressed politeness directed toward higher-status individuals) (Fukada and Asato, 2004, Shibatani, 1990, Yoshimura and Macwhinney, 2011). Humans commonly use polite language when addressing socially superior individuals; however, some languages, including Japanese, Korean, and Tibetan, include a complex system of honorifics, which represent “grammaticalized” outputs of politeness (Brown and Levinson, 1987). In contrast to animals’ submissive behavior, human verbal politeness is very sofisticated and related to multiple dimensions of social hierarchy, such as social intimacy/distance, age, profession and family/kinship.
Neuropsychological studies have reported impairments of social-hierarchy judgment associated with prefrontal cortex damage (Karafin et al., 2004, Mah et al., 2004). Neuroimaging have also investigated the brain processing of social hierarchy (Cheon et al., 2011, Chiao et al., 2009b, Freeman et al., 2009, Marsh et al., 2009, Muscatell et al., 2012, Zink et al., 2008). However, little is known about the neural representation of verbal politeness. A functional magnetic resonance imaging (fMRI) study showed involvement of Broca's area in grammatical aspects of honorific expression (Momo et al., 2008). Moreover, a Japanese case report described a patient with semantic dementia who used honorifics in all situations (Kokuryu and Takechi, 2011). However, to the best of our knowledge, the brain representation of politeness has not previously been investigated.
We investigated the neural correlates of verbal aspect of politeness using fMRI and transcranial direct-current stimulation (tDCS) by applying the honorific judgment task. Japanese honorification employs different verb forms for socially superior individuals (Shibatani, 1990). We hypothesized that an honorific-judgment task would activate brain areas associated with verbal politeness, in addition to language- or status recognition-related networks. Cathodal or suppressive tDCS with the same task confirmed the relationship between politeness and brain activation suggested by the fMRI analysis.
Section snippets
Subjects
Thirty-two right-handed healthy native Japanese university students participated in the experiments (mean age ± standard deviation [SD], 24.4 ± 5.0 years; five females and 27 males). To control the social ranking of the subjects, we recruited only university students for this experiment. None of the subjects had a history of any neurological or psychiatric disorders according to self-report. All were right-handed as assessed by the Edinburgh scale (Oldfield, 1971). All participants gave written
Experiment 1 (fMRI)
The mean accuracy rates were 0.95 ± 0.05, 0.98 ± 0.03, 0.98 ± 0.04 and 0.99 ± 0.01 for Politeness, Semantic, Syntax and Control conditions. For the mean accuracy rate, there was no significant difference using Friedman test. The mean RTs were 1659 ± 298.2, 1745 ± 322.2, 1692 ± 307.7 and 1459 ± 323.9 ms for Politeness, Semantic, Syntax and Control conditions. A repeated measures ANOVA demonstrated the significant effect of Condition on RT [F(3,60) = 15.191, p < 0.001]. Post hoc t-test showed the significance between
Discussion
Firstly, the present fMRI study revealed the precuneus activation associated with an honorific linguistic-expression task. The strength of precuneus activation during the politeness-judgment task was correlated with task performance. The precuneus was not significantly activated by the mere social-status judgment task. Secondarily, suppressive interference of the precuneus by cathodal tDCS worsened performance of the honorific judgment task but not other linguistic tasks. These findings
Competing interest
The authors declare no competing financial interests.
Acknowledgments
This study was partly supported by Grants-in-Aid for Scientific Research (B) (24300192) and for Exploratory Research (24650226) (to T.M.) from the Japan Society for the Promotion of Science.
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