Research reportInfluence of the cortical midline structures on moral emotion and motivation in moral decision-making
Introduction
Contemporary moral psychologists have studied the integrative model of human morality that can well explain the mechanism of moral motivation and actual moral behavior. Before the beginning of the 21st century, the mainstream paradigm in moral psychology was the Kohlbergian model, which attempted to explain the generation of moral behavioral motivation from a cognitive vantage point [1], [2]. However, this model has been criticized by proponents of the role of moral emotion [3] and intuition [4], [5]; those scholars have argued that the previous model was not able to successfully bridge the gap between moral reasoning and moral behavior [6]. Thus, to address this issue, contemporary moral psychologists have proposed an integrative model of human morality, which embraces the cognitive, affective and behavioral aspects. For instance, Neo-Kohlbergians, the contemporary moral psychologists who proposed integrative model of moral functioning (e.g., [7], [8], [9]), suggested the functional components of moral sensibility, moral motivation and moral personality on top of moral judgment [7]. In addition, character educators, who have sought to develop a new model of moral psychology that is suitable to educational practice, have underscored the integration of moral cognition, emotion and behavior [10], [11].
Then, what is the core or foundation of the integrative model? Which psychological construct does orchestrates activity of individual aspects of human morality and regulate the generation of motivational force for moral behavior? Several moral psychologists have suggested moral self as a candidate [12], [13], [14]. According to their theory, moral self is a psychological construct constituted by the perception of a person’s self as a moral person, which originates from moral identity [15]. Although a person might have developed sophisticated moral reasoning, he/she does not necessarily implement the result of his/her moral judgment into action if he/she does not possess a strong sense of moral self because he/she does not prioritize moral values over other self-oriented values [13], [16]. In fact, social psychological experiments have confirmed that the strength of moral self significantly moderated the relationship between the result of moral judgment [17], [18], perceived socio-moral emotional valence [19] and actual moral behavioral outcome. The formation and development of moral self occurs through reflection upon and deliberation of beliefs, values and previous life experience, and continued commitment to moral behavior [20]. During adolescence and even beyond, a person’s moral self is being consolidated by integrating moral values into his/her self-identity [14], [21].
Neuroimaging methods will facilitate this kind of research investigating the nature of human morality [22], [23]. Neuroimaging studies have contributed significantly to our understanding of human morality because they enable us to investigate the internal processes of moral functions that underlie overt human behaviors, which have not been measured by non-biological traditional methodologies [23], [24]. These studies also aim to avoid the potential social and desirable biases of self-reporting methods that have been problematic in traditional moral psychological studies [22].
Based on the previous studies, the present study aims to examine the relationship between the cortical midline structures (CMS), which have been regarded to be associated with selfhood, and moral decision making processes at the neural level. Previous fMRI studies in the field of cognitive and social neurosciences have examined the neural correlates of human morality. For instance, diverse dimensions of morality including, but not limited to, moral judgment [25], [26], moral sensibility [27], [28], [29], moral competence [30] and moral elevation [31], [32] have been demonstrated. Furthermore, several social neuroscientists have proposed the presence of the co-activation of selfhood-related regions, particularly those in the cortical midline structures (CMS) during the processing of moral tasks. The CMS include the dorsal- and ventral-medial prefrontal cortices (MPFC) and cingulate cortex [33], [34]. Recent meta-analyses [35], [36] and fMRI studies [37], [38] have also demonstrated that the processing of self-related and familiar contexts is associated with activity in the CMS regions, including the MPFC, PCC and anterior cingulate cortex (ACC). However, some studies have shown that in certain instances, activity in the posterior medial cortices (PMC) in the CMS was not stronger in “self” conditions compared to “others” conditions; more specifically, the region showed significantly stronger activity in the distant-others condition compared to the self condition in general [36], [37]. Given these studies, it would be possible to say that the MPFC is commonly associated with selfhood-related processes, but the PMC is particularly associated with autobiographical memory processing rather than selfhood-related processes in general [37]. In studies related to morality, neuroimaging studies have also shown the relationship between the CMS regions and morality-related task conditions. In the previous fMRI studies, activity in the CMS regions was commonly associated with moral task conditions [39], [40], [41]. In addition, self-agency related to moral functioning shared neural substrates with the CMS [42]. Given these previous studies, we expect that there is significant relationship between the neural correlates of moral functioning and selfhood-related processes. The present study uses the general linear model (GLM) method to conduct the whole-brain tests; this method enables us to conduct “a diverse interrogation of functional imaging data using statistical parametric maps (p. 202)” and a diverse statistical analysis from a t-test to ANCOVA [43].
Given these studies in social neuroscience demonstrating the activation of the CMS regions in morality-related task conditions, we can expect a significant overlap between the brain circuitries associated with moral functioning and selfhood-related psychological processes. Moreover, the nature of moral dilemmas would cause increased activity in such regions compared to non-moral dilemmas. Usually, moral dilemmas are regarded as problem sets that deal directly with “what we have to do” or “what we ought to do,” while non-moral dilemmas are in the realm of fact, instead of value [44]. Particularly, moral-personal dilemmas (e.g., Footbridge dilemma) are closely associated with the possible violation to concrete human lives; on the other hand, moral-impersonal dilemmas (e.g., Trolley dilemma) do not directly request subjects to make decisions affecting concrete human lives, but are similar to mathematical calculation problems [25], [26], [45]. Since moral dilemmas are more likely to urge us to deliberate upon our moral beliefs and values, they would induce stronger activity in the CMS regions compared to non-moral dilemmas.
Furthermore, although traditional moral psychologists did not use neuroimaging methods, their social psychological [13], [17], [18], [46] and developmental psychological studies [14], [20] have shown the moderating and monitoring role of moral self in moral functioning. Thus, we may also expect that brain activity in the CMS associated with selfhood moderates or even influences that in other regions associated with moral functioning. However, the previous studies that have shown the overlap between those two brain circuitries did not utilize analytic methods that enable us to see the interaction between or causal relationship between brain regions, such as the psycho-physiological interaction (PPI) analysis [47] and Granger causality analysis [48]. The problem of reverse inference occurs if we try to interpret findings without the application of proper experimental and analysis methods [49], [50]. Therefore, the present study aims to investigate such possible moderating and causal relationship between the CMS and other regions associated with moral functioning in morality-related task conditions, using the PPI analysis and GCA methods when subjects are making moral decisions to address moral problems.
The present study hypothesizes that first, the whole-brain tests will demonstrate that brain regions associated with emotional processes will show greater activity in the moral-personal condition compared to the moral-impersonal condition. This hypothesis originates from previous neuroimaging studies utilizing similar dilemma task conditions [25], [26], [51]. Moral-personal dilemmas are more likely to induce significant activity in regions associated with emotion (e.g., MPFC, orbitofrontal cortex (OFC), superior-temporal sulcus (STS), insula [42], [51], [52], [53], [54], [55]) compared to moral-impersonal dilemmas, because the former strongly induce negative immediate emotional responses among subjects. On the other hand, previous studies have shown that in the moral-impersonal condition, regions associated with cognition, such as mental calculation (e.g., parietal lobule), will show significantly increased activity [25], [26], [51], [56].
Second, activity in the CMS regions significantly moderates activity in other brain regions associated with moral emotion and motivation (e.g., midbrain including the ventral tegmental area, ventral striatum, insula, OFC [57], [58], [59], [60], [61]) while subjects are solving moral problems. Given previous neuroimaging studies showing the overlap between the two regions, and traditional moral psychological studies suggesting the role of moral self, the present study will be able to find significant PPI between CMS and other regions associated with morality in the moral-task condition. Particularly, the present study focuses on the MPFC and posterior cingulate cortex (PPC) in the CMS. First, the MPFC is associated with self-referencing and self-evaluation [62], [63], [64], which are fundamental to moral decision making processes. These selfhood-related psychological processes enable people to consider and reflect upon their moral belief and value and to make a decision based on them [14], [20], [65]; moral decision making also would be moderated by these processes. Second, the present study also focuses on the PCC, because this region is associated with the processing of autobiographical memory, including self-referencing [33], [37], [66], [67], [68], [69]. Of course, although the PCC would not be strongly associated with selfhood-related processes in general, because this region is associated with the autobiographical memory processing [36], [37], the core self-related process involved in moral decision making, the present uses this region as a seed region. Because moral judgment cannot be independent from and is influenced by the deliberation upon previous lifelong experience [14], [20], [70], autobiographical memory processes inevitably would be involved in moral judgment, as the proponents of moral self and moral identity suggest [71], [72]. Given these, the present study focuses on the MPFC and PPC, which are closely associated with selfhood-related psychological processes.
Third, given the role of moral self proposed by traditional moral psychologists, the present study expects causal influence from activity in the CMS to that in other brain regions associated with moral emotion and motivation. The GCA will demonstrate significant causal influence from the MPFC and PPC to brain regions associated with moral emotion and motivation. More specifically, among all brain regions associated with morality, the present study concentrates on the insula regions, including both the anterior (AI) and posterior insula (AI). First, previous experiments have demonstrated that the PI is the core of the immediate processing of affective responses and the induction of subjective feelings [73], [74], particularly negative emotions (e.g., pain and disgust) [73], [74], [75], [76], [77], that play fundamental roles in moral cognition [42], [53]. Moreover, the AI is closely associated with the integration of cognition and emotion [78], [79], [80], [81], [82], conscious and interceptive awareness, monitoring of aroused emotional responses [28], [83], [84], and finally, the modulation of motivational force [60], [61], [85]. Given these previous works, the present study chooses the AI and PI as the regions of interest for the GCA.
Section snippets
Subjects
The present study recruited sixteen subjects at a college located in Northern California, using university mailing lists and Facebook. Only healthy right-handed subjects were included to control for any possible compounding effect originated from a history of physical or mental illness and handedness. Subjects' physical and mental health condition (e.g., allergies, kidney problems, seizures, claustrophobia) was tested using a standard self-reporting questionnaire developed by The Richard M.
Whole brain analyses
We conducted whole-brain t-tests to examine whether the present experiment replicated well previous studies that used a similar dilemma set. Two contrasts (i.e., moral-personal versus control and moral-impersonal versus control) applied to the analyses. Furthermore, we also compared brain activity between those two dilemma types. The results are summarized in Table S2 and displayed in Fig. 2. These results demonstrated that the MPFC and ACC showed significantly great activity under the
Discussion
First, the present study compared the neural-level activity under the moral-personal, moral-impersonal and control conditions through whole-brain t-tests. The comparison showed that the MPFC was particularly activated under the moral-personal condition, while the parietal lobule regions were significantly activated under the moral-impersonal condition. These whole-brain t-tests successfully replicated previous fMRI investigations that utilized similar moral dilemmas [25], [26], [51]. Second, we
Conclusion
The present study demonstrates significant interactions developed between the CMS (PCC and MPFC) and other moral-related regions including AI and PI while subjects are solving moral dilemmas. These results can support the moral psychological accounts regarding the role of moral self in moral decision-making processes. Particularly, motivational processes for moral decision-making is coupled with activity in CMS regions, which is regarded as an indicator of the involvement of selfhood-related
Disclosure
The authors report no conflicts of interest.
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