Circadian Typology And Response Inhibition: Behavior And FMRI Study

Circadian rhythmic expression differs among individuals and can be classified by circadian typology, which can be classified as morningness, eveningness and neither type. Individual differences in circadian rhythms are treated as an interesting aspects of personality study (Randler, 2008). Although the construct presents a continuum (Natale & Cicogna,2002), two ends are viewed in a dichotomous manner contrasting ’larks’ and ’owls’.’Larks’ are morning types, getting up early, performing mentally and physically better in the morning and going to bed also early.’Owls’, on the other side, prefer to stay out late, get up at a later time, and performing best in the late afternoon or evening, both mentally and physically. Tonetti et al. (2010) considered the eveningness and personality traits such as impulsivity (Adan, Natale, Caci,& Prat,2010; Selvi et al.,2011), novelty seeking (Adan, Lachica, Caci,& Natale,2010; Caci, Robert,& Boyer,2004), and sensation seeking (Tonetti et al.,2010.)are significant correlation. These personality traits, different in name, but this difference is largely owe to the different personality models, in fact, there are similarities in the implications, that may reveal the relationships between eveningness with these personality traits are stable. The research results showed that, the morningness is more likely to be the future time orientation, and eveningness is the present time orientation (Kati & Elke,2013; Taciano & Miriam, 2014) and delayed gratification ability of eveningness is worse. Using path analysis, researchers explained that self-control may play a part in the regulation, eveningness’s low self-control ability then adjust the present time orientations and delayed gratification ability (Taciano & Miriam,2014). Response inhibition is an important aspect of executive function refers to the ability to inhibit does not meet current needs or inappropriate behavioral responses, people to make a flexible and goal-directed behavior based on changes in the environment is essential (Logan & Cowan,1984). Response inhibition are associated with self-control and impulsivity, the behavioral assessment of impulsivity will focus on objective laboratory tasks of response inhibition (Andrea & Trevor,2013), self-control is the aspect of inhibitory control that involves control over one’s behavior and control over one’s emotions in the service of controlling one’s behavior. Self-control is about resisting temptations and not acting impulsively. The final aspect of self-control-delaying gratification making yourself forgo an immediate pleasure for a greater reward later. Researchers studied from different perspectives, such as genes, lifestyle, personality, emotion, etc. However, circadian typology in higher cognitive functions, such as executive function is still poorly understood. Are there differences in the eveningness compared with the morningness on the ability of executive function will be the starting point of this study. In view of the existing research has pointed out that, eveningness in personality questionnaire of impulsiveness, sensation seeking, novelty seeking scores are high, low self-control and are more susceptible to attention deficit hyperactivity disorder, substance abuse; this study will focus on the key ingredients of executive function:response inhibition. The present study conducted two experiments and the results were follows.In the first behavioral study, we chose morningness and eveningness, which is screened by classical MEQ as the between-group variables; chose the test of time, in the morning and evening as the within-group variables, using the Stop-Signal paradigm of the classic response inhibition, task the Stop-Signal RT(SSRT) index of ability to the level of inhibit response as the dependent variable, by means of two-factor repeated measures ANOVA methods to explore the interaction between circadian typology and time of day in response inhibition performance. The results showed that, the interaction and the main effect of the two factors in Stop-Signal task, both of them were not significant. In other words, in this behavioral experiment, response inhibition is not affected by the circadian typology and time of day.Using functional magnetic resonance imaging (fMRI), the second studies still use the stop-signal paradigm same as the first experiment, in the scanning process which subjects were asked to complete the Stop-Signal task, experimental design is similar as the first experiment, to explore the neural mechanisms between circadian typology and time of day in response inhibition. The behavior results of fMRI experiments is similar as the first behavioral study, the interaction and the main effect of the two factors in Stop-Signal task, both of them were not significant. But fMRI results showed that, three factors included circadian typology, time of day and the type of reaction (go, stop) interact to activate brain regions including the typical brain areas of cognitive control, such as frontal gyrus, inferior frontal gyrus, medial forehead gyrus and inferior parietal lobule and includes temporal gyrus and subcortical regions-the caudate nucleus. ROI analysis results showed that the intensity of the activities of the various brain regions exhibited the significant interaction between circadian typology and time of day, specifically, the activity in these brain regions of morningness in the early morning is stronger than tested at night, meanwhile, the activity in these brain regions of eveningness at night is stronger than tested in the early morning. These results may reveal the activity of morningness and eveningness in response inhibition exhibited corresponding to its own biological rhythm.Comprehensively, the results showed that:(1) At the behavioral level, circadian typology and time of day two factors had no significant effect on response inhibition, but at the brain level, showing the significant effect between the two factors, results in brain activity areas of interest, circadian typology and time of day is significant interaction. (2) The neural mechanism of morningness and eveningness in the response inhibition is corresponding to their own biological rhythm. That is to say, the activity in these brain regions of morningness in the early morning is stronger than tested at night, meanwhile, the activity in these brain regions of eveningness at night is stronger than tested in the early morning. In the present study, we offered a unique perspective on combination circadian typology with response inhibition, broaden the research field of circadian typology. we believed that our research provides a new perspective and evidence in relation study between circadian typology and executive function, which could offer important scientific and practical value.