In the present fMRI study, we required the subjects to assess the degree of goodness or badness, as well as the degree of beauty or ugliness of moral behaviors in daily life, to determine whether morality judgment and moral aesthetic judgment differ in their neural underpinnings or not. Behavioral results revealed that the rating of morality judgment was significantly higher than those of moral aesthetic judgment for the same moral behavior, indicating that people may be more inclined to make morality judgment. The fMRI results revealed that when the same experimental material was used, but varying task demands were systematically considered, the distinct nervous systems of morality judgment and moral aesthetic judgment emerge with more clarity. Specifically, direct contrasts showed specific activations for morality judgment; these were mainly located in the frontal, parietal and occipital cortex, including the bilateral SMA, IPL/SPL, MFG/pars opercularis of IFG extending onto the ventral premotor cortex (PMv), and IOG/MOG: i.e., brain regions which have been previously reported for motor representations of behavior during understanding others` behaviors (Finisguerra et al., 2021; Heleven & Van Overwalle, 2018). These areas are only sensitive to goodness and badness, but not to beauty and ugliness. In contrast, moral aesthetic judgment significantly elicited specific activations in the frontal, parietal and temporal cortex, including the bilateral ACC/mPFC/mOFC, PCC/Precuneus, TPJ and anterior insula: i.e., brain regions which have been proved to be involved in understanding other people's behavioral intentions and emotions (Heleven & Van Overwalle, 2018). These areas are only sensitive to beauty and ugliness, but not to goodness and badness. Interestingly and more importantly, when subjects judged a behavior to be good (as in contrast to bad) or to be beauty (as in contrast to ugly), the lateral OFC showed enhanced BOLD signals, which was in line with what was found in recent study that lateral OFC was commonly involved in the processing of goodness and beauty (Cheng et al., 2020). But no common brain region was found to be involved in the processing of badness and ugliness. Against the background of the literature, present findings indicate that morality judgment and moral aesthetic judgment seemly activate completely different cortical networks, although lateral OFC is commonly activated in both moral goodness and beauty.
The OFC is critical for goal-directed behavior (Dolan et al., 1996; Elliott et al., 2000; Rich & Wallis, 2014). Converging neuroimaging evidence shows differences between lateral OFC and medial OFC (Carmichael & Price, 1994, 1995; Kahnt et al., 2012; Kringelbach & Rolls, 2004; Liu et al., 2010; Neubert et al., 2015; J. O’Doherty et al., 2001; Ongür & Price, 2000; Zald et al., 2014), the medial OFC in general is concerned with monitoring reward values (Brown et al., 2011; Dio et al., 2007; Kawabata & Zeki, 2004; Kirk et al., 2009; Liang et al., 2010; Mende-Siedlecki et al., 2013; J. P. O’Doherty et al., 2003; Winston et al., 2007), but the lateral OFC connecting the anterior insula cortex is generally involved in the processing of affectively stimuli (Morrison & Salzman, 2009; Murray et al., 2007). We found that both moral goodness and moral beauty more strongly activated the lateral OFC/anterior insula, suggesting that this brain region may be involved in encoding the emotional experiences that often occur in human interactions. As moral goodness and moral beauty judgments share a very critical characteristic, that is, the object of both judgments generally refers to the positive moral behavior. This result is not surprising given that positive moral behavior is a rewarding stimulus that evokes emotional experiences.
It is important to mention, we found that the medial OFC, with strong connections with vmPFC and ACC, not only responded to moral beauty, but also responded to moral ugliness, and there was indifferent in response intensity between them. Due to strong connections among OFC, vmPFC and ACC a network was suggested – the orbital medial prefrontal cortex (OMPFC) – related to emotion processing and social cognition (Avram, 2013; Ongür & Price, 2000). Traditionally, the mOFC has commonly been suggested as an important reward-related region involved in the processing of beauty or positive stimuli (Cloutier et al., 2008; Ishizu & Zeki, 2011; Kawabata & Zeki, 2004, 2008; Kirk et al., 2009; J. O’Doherty et al., 2001), however, recent work show that the mOFC was activated by negative experiences (Plassmann et al., 2010; Tajima et al., 2010), and also was involved alike by both the beautiful and the ugly stimuli (Martín-Loeches et al., 2014). The mOFC, as a part of the medial cortical structures involved in self-referential and self-related processes (Northoff et al., 2006), has been proved not only to be involved in self-perception in social cognition (Flagan & Beer, 2013), but also engaged in coding internal motivational values, particularly in the absence of external prompts (Bouret & Richmond, 2010). Consistent with the above findings, the result that both moral beauty and moral ugliness significantly activated the OMPFC might be interpreted as the activation of neural circuits related to self vs. other-assessment (Martín-Loeches et al., 2014). In the moral aesthetic judgment, people usually evaluate the inner beauty or ugliness of others through morally behavioral understanding, in which their mental status will be perceived and be compared with ourselves. And the mOFC or OMPFC might play a crucial role in this process.
In the present study, people usually focus on the action itself (Ellemers, 2018; Ellemers et al., 2019) and are emotionally unmoved (Diessner et al., 2006; Güsewell & Ruch, 2012a, 2012b) when they judge whether a moral behavior is good or bad. Behaviors directed by morality judgment are cognitively experienced and judged without deep emotional involvement (Diessner et al., 2008). However, when people evaluate a person's inner beauty or ugliness according to his moral behavior, people's emotions are easily affected by his behavior: that is, if he acts good, people`s emotions are elevated (Algoe & Haidt, 2009; J. Haidt, 2003b, 2003a, 2006; J. Haidt & Keltner, 2004; Keltner & Haidt, 2003); If he acts evil, people feel contempt, anger or disgust (J. Haidt, 2002), and the emotion is unpleasant. Both morality judgment and moral aesthetic judgment are accomplished by behavioral understanding. Understanding the behaviors of others will contribute to the harmony of people`s interpersonal relationships, and is necessary for efficient communication and collaboration, which deals primarily with what they are doing, how they are doing it (i.e., behavioral states), and why they are doing it (i.e., mental states) (Chiavarino et al., 2012; Spunt et al., 2016), and is accomplished by two processes and related brain networks: motor representation of behavior and intention representation of behavior, supported by the mirror neuron system (MNS) and the mentalizing system (MZS), respectively (Heleven & Van Overwalle, 2018). Prior neuroimaging studies have shown that the MNS and the MZS are differentially activated by what/how and why questions about behaviors (Spunt et al., 2016).
Cortical areas with motor properties, including inferior frontal gyrus (IFG), ventral premotor cortex (PMv) and inferior parietal lobule (IPL), namely, the MNS, have been observed to respond to motor behaviors when they are performed and observed (G. Buccino et al., 2001; Giovanni Buccino et al., 2004; Kemmerer, 2015; Kemmerer et al., 2012; Li et al., 2020; Molenberghs et al., 2012; Pulvermüller, 2013; Rizzolatti et al., 2014; Urgesi et al., 2014), reflecting motor representation of behavior (Spunt et al., 2010, 2011; Spunt & Adolphs, 2014; Spunt & Lieberman, 2012a, 2012b). Li et al., (2020) recently used fNIRS to examine the brain activity in the frontal, motor, parietal and occipital regions, aiming to better understand the brain correlates involved in encoding motor complexity. They found that motor complexity sensitive brain regions were present in the pars opercularis IFG/PMv, primary motor cortex (M1), IPL/supramarginal gyrus and middle occipital gyrus (MOG) during behavior execution, and in pars opercularis IFG/PMv and M1 during behavior observation, suggesting that the processing of motor complexity involves not only M1 but also pars opercularis IFG, PMv and IPL, each of which plays a critical role in behavior perception and execution (Li et al., 2020). Some studies that used transcranial magnetic stimulation (Ishibashi et al., 2011; Populic et al., 2010) found that the left IPL is involved in the representation of the manipulability of the objects, while the temporal cortex includes more abstract representation of object function. Spun et al. (2012) found that there existed a dissociation between the posterior and anterior regions of IFG in their contribution to behavior representation (Badre & D’Esposito, 2009; Kilner, 2011; Spunt & Lieberman, 2012a): The pIFG/PMv is associated with the perception of behaviors and the execution of understanding behaviors, mainly manifesting in encoding more concrete representations of behaviors -- “what” and “how”; and the anterior IFG region located in the ventrolateral PFC is associated with the motive of understanding behaviors, mainly manifesting in encoding more abstract representations of behaviors - “why”. In the present study, we found that compared with moral aesthetic judgment, morality judgment, both good reaction and bad reaction, recruited motor-related areas, including MFG/IFG/PMv, SMA, SPL/IPL and IOG/MOG, indicating that morality judgments might use motor representation through “body” reading, supported by the MNS (Keysers & Fadiga, 2008; Rizzolatti & Sinigaglia, 2010; Spunt & Lieberman, 2012b; Van Overwalle, 2009) which is part of a larger sensorimotor brain network, to complete assessments of whether a moral behavior is good or bad and how good or bad it is. It is worth noting that the brain network for morality judgment is more consistent with that for the behavior execution than with that for the behavior observation.
Although the human MNS is reliably active during behavior understanding, several studies have shown that it is insensitive to the intentional representation of observed behavior; rather, a separate brain system known as the ToM or mentalizing system (MZS), by inferring the internal states of other persons that typically drive behaviors, such as their goals, desires, beliefs, intentions, causal attributions and traits, appears to be critical (Brass et al., 2007; de Lange et al., 2008; Grèzes et al., 2004; Spunt et al., 2011). It is part of a larger default brain network, including the medial PFC, PCC/precuneus and the TPJ. We found no activation of brain regions associated with mentalizing in morality judgment, which is consistent with the result from a recent study (Yoder & Decety, 2014). In this study, Yoder and Decety (2014) scanned 40 healthy adults using fMRI while these subjects watched scenes in which people harmed or helped others. They found that subjects sensitive to righteous actions activated brain regions associated with (social) cognitive aspects of morality judgment, rather than with processing emotional aspects of a moral scenario. Mentalizing, in particular, empathy, may not be necessary for deciding whether moral behaviors are right or wrong, but it may still play an important role in the motivation of moral behavior (Will & Klapwijk, 2014).
The MZS is usually activated by why questions about behaviors is responsive to tasks of mental-state reasoning (Amodio & Frith, 2006; Carrington & Bailey, 2009; Gallagher & Frith, 2003; Saxe & Powell, 2006; Schurz et al., 2014; Van Overwalle & Baetens, 2009). The brain regions of the MZS are involved in the multifunctional process of distinguishing oneself from the thoughts of others and gaining an understanding of their mental status, which in turn enable people to recognize, interpret, and predict behavior (Fan et al., 2011; Singer & Lamm, 2009). In the present study, when the subjects were required to evaluate the beautiful or ugly degree of the moral behaviors, brain regions consistent with the MZS were activated, suggesting that the processing of moral aesthetics is likely to be supported by the MZS. In the process of moral aesthetic judgment, people are likely to understand the social actor`s moral behavior and make a judgment of beauty or ugliness by reasoning the mental status that typically drive behavior, such as beliefs, desire and intentions. moral aesthetic judgment may require psychological reflection or, more generally, a shift in attention to the social actor's intention. The neural mechanism for the question of how beautiful or ugly the moral behavior is seems to be the same as the neural mechanism for the question of why the behavior is done. By manipulating either behavior goals or the content of a perceived behavior (Brass et al., 2007; de Lange et al., 2008; Grèzes et al., 2004), Thioux et al. (2008) found that the MNS supported the understanding behaviors at low (how) and intermediate (what) levels of abstraction, whereas the MZS supported the understanding behaviors at high (what) levels of abstraction (Thioux et al., 2008; Vallacher & Wegner, 1987).
In addition, in moral aesthetic judgment, the beauty or ugliness of moral behavior generally refers to the beautiful or ugly of social actor's personality traits (Diessner et al., 2013), and the traits inference always involves the activiations of TPJ and mPFC (Van der Cruyssen et al., 2009; Van Duynslaeger et al., 2007). In addition to regions implicated in mentalizing, we found that moral aesthetics also recruited the activation of anterior insula. This region is not only implicated in the meta-representation of emotional states and interoceptive awareness (Cauda et al., 2012; A. D. Craig, 2002; A. D. B. Craig, 2009; Kurth et al., 2010), but also correlates with the cognitive processing of self and others (Sperduti et al., 2011), particularly is critical for the perceived intentionality of other people`s behavior (Liljeholm et al., 2014). In short, moral aesthetic judgment refers to the perceiver's judgment on the inner beauty of others, which seems to be concerned with the internal processes that underlie a perceiver’s aesthetic experience. This process has been reported to be supported by the cortical network implicated in the mentalizing system.