Gender Differences in Neural Mechanisms Underlying Moral Sensitivity
Gender Differences in Neural Mechanisms Underlying Moral Sensitivity
Researchers have proposed that females and males differ in the structure of their moral attitudes, such that females tend to adopt care-based moral evaluations and males tend to adopt justice-based moral evaluations. The existence of these gender differences remains a controversial issue, as behavioral studies have reported mixed findings. The current study investigated the neural correlates of moral sensitivity in females and males, to test the hypothesis that females would show increased activity in brain regions associated with care-based processing (posterior and anterior cingulate, anterior insula) relative to males when evaluating moral stimuli, and males would show increased activity in regions associated with justice-based processing (superior temporal sulcus) relative to females. Twenty-eight participants (14 females) were scanned using fMRI while viewing unpleasant pictures, half of which depicted moral violations, and rated each picture on the degree of moral violation that they judged to be present. As predicted, females showed a stronger modulatory relationship between posterior cingulate and insula activity during picture viewing and subsequent moral ratings relative to males. Males showed a stronger modulatory relationship between inferior parietal activity and moral ratings relative to females. These results are suggestive of gender differences in strategies utilized in moral appraisals.
The existence of gender differences in moral reasoning has been an issue of much controversy and debate. Gilligan (1977) claimed that men and women speak in a different ‘moral voice’. Specifically, women are believed to typically approach moral dilemmas with a care-based orientation that emphasizes maintenance of interpersonal relationships and is guided by social emotions including empathy and altruism (Robertson et al., 2007), whereas men typically approach moral dilemmas with a justice-based orientation that emphasizes maintenance of order and adherence to rules and obligations. However, despite numerous behavioral studies comparing moral decision-making in males and females, little evidence has been found to support Gilligan's arguments (Jaffee and Hyde, 2000; Hyde, 2005; but see Skoe et al., 2002).
Previous research investigating gender differences in moral reasoning has been limited primarily to behavioral techniques such as coding verbal responses to hypothetical moral dilemmas (Jafee and Hyde, 2000). Complementary techniques, such as neuroimaging, have the potential to yield new insight into gender differences in moral reasoning, since behavior can be considered the sum result of all neural activity (Canli and Amin, 2002). In other words, patterns of brain activity during moral processing might differ for males and females despite similar behavioral outcomes. Although researchers have begun investigating the neural basis of moral emotion and cognition (Greene et al., 2001,2004; Moll et al., 2002a,2002b; Heekeren et al., 2003,2005; Harenski and Hamann, 2006; Schaich Borg et al., 2006), the neural basis of gender differences in moral processing has not been explored.
Functional neuroimaging studies of moral appraisal have identified a consistent set of brain regions that are involved in processing different types of moral stimuli including moral dilemmas, statements and pictures (Greene and Haidt, 2002; Moll et al., 2005; Raine and Yang, 2006). These stimuli typically describe or show examples of ‘moral violations’, such as one person intentionally causing harm to another. Tasks that involve processing these types of stimuli reliably activate regions of inferior parietal cortex, including the posterior superior temporal sulcus and temporo-parietal junction, which may represent the contribution of theory of mind processes to moral decision-making, and the medial prefrontal cortex, which may represent the integration of emotional responses into moral decision-making (Greene and Haidt, 2002; Moll et al., 2005; Koenigs et al., 2007). Another region, the posterior cingulate (and adjacent precuneus region), has been implicated in moral appraisal in some studies (Greene et al., 2001,2004; Heekeren et al., 2005; Harenski and Hamann, 2006) but not others (Moll et al., 2002a,2002b; Heekeren et al., 2003). It has been suggested that this region may represent emotion and memory processes in the context of moral appraisal (Greene and Haidt, 2002). This region has also been implicated in other affective and cognitive processes including autobiographical emotional recall (Fink et al., 1996; Maddock, 1999), and is believed to link emotion and memory processes (Maratos et al., 2001; Maddock et al., 2003). More recently, activity in this region has been shown to contribute to experiential self reflection (Johnson et al., 2006).
Posterior cingulate activity in response to moral stimuli may be related to the gender composition of the study sample, such that females are more likely to show activity in this region in response to moral stimuli than are males (Harenski and Hamann, 2006). This hypothesis fits well with a recent study in which participants showed increased posterior cingulate activity in response to care-based moral dilemmas relative to justice-based moral dilemmas (Robertson et al., 2007). In contrast, increased activity during justice-based relative to care-based dilemmas occurred in the posterior superior temporal sulcus. Care-based dilemmas were designed to represent concerns regarding the welfare of others, and to elicit empathic emotions such as compassion and benevolence. Justice-based dilemmas were designed to represent concerns regarding the liberation of others from injustice, and to elicit attitudes of fairness and impartiality. Although the participants in this study were male, and gender differences were not explored, if females indeed have stronger care-based orientations to moral stimuli relative to males they should show greater posterior cingulate activity associated with moral processing (when making moral appraisals that are not explicitly designed to elicit care- or justice-based judgments). Since care-based moral appraisals are also expected to invoke empathic responses, females should also show increased neural activity associated with empathic processes. Recent studies investigating the neural correlates of empathy have implicated two primary regions; the anterior insula and dorsal anterior cingulate cortex (Botvinick et al., 2005; Singer et al., 2004,2006; Jackson et al., 2005,2006; Saarela et al., 2007; Lamm et al., 2007). Regarding males, if they indeed have stronger justice-based orientations to moral stimuli relative to females, they should show greater posterior superior temporal sulcus activity during moral processing. The current study tested these hypotheses.
In the current study, we used functional magnetic resonance imaging (fMRI) to examine gender differences in neural responses to pictures depicting moral violations. We also assessed gender differences in behavioral moral evaluations by obtaining online ratings of the severity of depicted moral violations. In contrast to most prior neuroimaging studies of moral appraisal, which have typically compared averaged neural responses to a set of ‘moral’ and ‘non-moral’ stimuli, the current study design allowed us to explore the association between neural activity in response to individual moral pictures and subsequent moral violation severity ratings. Specifically, we conducted a parametric modulation analysis in which we explored brain regions whose activity during moral picture viewing positively modulated subsequent moral violation severity ratings. Thus, the current design is sensitive to individual variation in responses to diverse moral stimuli. We explored whether activity in specific brain regions was positively correlated with moral severity ratings, and whether these regions differed for males and females. The primary hypothesis was that females would show a greater positive modulation of moral severity ratings by activity in the posterior cingulate, anterior insula, and dorsal anterior cingulate during moral picture viewing relative to males. In addition, we hypothesized that males would show a greater positive modulation of moral severity ratings by activity in posterior superior temporal sulcus during moral picture viewing relative to females. Whether we would observe gender differences in other neural correlates of moral processing, such as medial prefrontal cortex, was an open question.
Abstract and Introduction
Abstract
Researchers have proposed that females and males differ in the structure of their moral attitudes, such that females tend to adopt care-based moral evaluations and males tend to adopt justice-based moral evaluations. The existence of these gender differences remains a controversial issue, as behavioral studies have reported mixed findings. The current study investigated the neural correlates of moral sensitivity in females and males, to test the hypothesis that females would show increased activity in brain regions associated with care-based processing (posterior and anterior cingulate, anterior insula) relative to males when evaluating moral stimuli, and males would show increased activity in regions associated with justice-based processing (superior temporal sulcus) relative to females. Twenty-eight participants (14 females) were scanned using fMRI while viewing unpleasant pictures, half of which depicted moral violations, and rated each picture on the degree of moral violation that they judged to be present. As predicted, females showed a stronger modulatory relationship between posterior cingulate and insula activity during picture viewing and subsequent moral ratings relative to males. Males showed a stronger modulatory relationship between inferior parietal activity and moral ratings relative to females. These results are suggestive of gender differences in strategies utilized in moral appraisals.
Introduction
The existence of gender differences in moral reasoning has been an issue of much controversy and debate. Gilligan (1977) claimed that men and women speak in a different ‘moral voice’. Specifically, women are believed to typically approach moral dilemmas with a care-based orientation that emphasizes maintenance of interpersonal relationships and is guided by social emotions including empathy and altruism (Robertson et al., 2007), whereas men typically approach moral dilemmas with a justice-based orientation that emphasizes maintenance of order and adherence to rules and obligations. However, despite numerous behavioral studies comparing moral decision-making in males and females, little evidence has been found to support Gilligan's arguments (Jaffee and Hyde, 2000; Hyde, 2005; but see Skoe et al., 2002).
Previous research investigating gender differences in moral reasoning has been limited primarily to behavioral techniques such as coding verbal responses to hypothetical moral dilemmas (Jafee and Hyde, 2000). Complementary techniques, such as neuroimaging, have the potential to yield new insight into gender differences in moral reasoning, since behavior can be considered the sum result of all neural activity (Canli and Amin, 2002). In other words, patterns of brain activity during moral processing might differ for males and females despite similar behavioral outcomes. Although researchers have begun investigating the neural basis of moral emotion and cognition (Greene et al., 2001,2004; Moll et al., 2002a,2002b; Heekeren et al., 2003,2005; Harenski and Hamann, 2006; Schaich Borg et al., 2006), the neural basis of gender differences in moral processing has not been explored.
Functional neuroimaging studies of moral appraisal have identified a consistent set of brain regions that are involved in processing different types of moral stimuli including moral dilemmas, statements and pictures (Greene and Haidt, 2002; Moll et al., 2005; Raine and Yang, 2006). These stimuli typically describe or show examples of ‘moral violations’, such as one person intentionally causing harm to another. Tasks that involve processing these types of stimuli reliably activate regions of inferior parietal cortex, including the posterior superior temporal sulcus and temporo-parietal junction, which may represent the contribution of theory of mind processes to moral decision-making, and the medial prefrontal cortex, which may represent the integration of emotional responses into moral decision-making (Greene and Haidt, 2002; Moll et al., 2005; Koenigs et al., 2007). Another region, the posterior cingulate (and adjacent precuneus region), has been implicated in moral appraisal in some studies (Greene et al., 2001,2004; Heekeren et al., 2005; Harenski and Hamann, 2006) but not others (Moll et al., 2002a,2002b; Heekeren et al., 2003). It has been suggested that this region may represent emotion and memory processes in the context of moral appraisal (Greene and Haidt, 2002). This region has also been implicated in other affective and cognitive processes including autobiographical emotional recall (Fink et al., 1996; Maddock, 1999), and is believed to link emotion and memory processes (Maratos et al., 2001; Maddock et al., 2003). More recently, activity in this region has been shown to contribute to experiential self reflection (Johnson et al., 2006).
Posterior cingulate activity in response to moral stimuli may be related to the gender composition of the study sample, such that females are more likely to show activity in this region in response to moral stimuli than are males (Harenski and Hamann, 2006). This hypothesis fits well with a recent study in which participants showed increased posterior cingulate activity in response to care-based moral dilemmas relative to justice-based moral dilemmas (Robertson et al., 2007). In contrast, increased activity during justice-based relative to care-based dilemmas occurred in the posterior superior temporal sulcus. Care-based dilemmas were designed to represent concerns regarding the welfare of others, and to elicit empathic emotions such as compassion and benevolence. Justice-based dilemmas were designed to represent concerns regarding the liberation of others from injustice, and to elicit attitudes of fairness and impartiality. Although the participants in this study were male, and gender differences were not explored, if females indeed have stronger care-based orientations to moral stimuli relative to males they should show greater posterior cingulate activity associated with moral processing (when making moral appraisals that are not explicitly designed to elicit care- or justice-based judgments). Since care-based moral appraisals are also expected to invoke empathic responses, females should also show increased neural activity associated with empathic processes. Recent studies investigating the neural correlates of empathy have implicated two primary regions; the anterior insula and dorsal anterior cingulate cortex (Botvinick et al., 2005; Singer et al., 2004,2006; Jackson et al., 2005,2006; Saarela et al., 2007; Lamm et al., 2007). Regarding males, if they indeed have stronger justice-based orientations to moral stimuli relative to females, they should show greater posterior superior temporal sulcus activity during moral processing. The current study tested these hypotheses.
In the current study, we used functional magnetic resonance imaging (fMRI) to examine gender differences in neural responses to pictures depicting moral violations. We also assessed gender differences in behavioral moral evaluations by obtaining online ratings of the severity of depicted moral violations. In contrast to most prior neuroimaging studies of moral appraisal, which have typically compared averaged neural responses to a set of ‘moral’ and ‘non-moral’ stimuli, the current study design allowed us to explore the association between neural activity in response to individual moral pictures and subsequent moral violation severity ratings. Specifically, we conducted a parametric modulation analysis in which we explored brain regions whose activity during moral picture viewing positively modulated subsequent moral violation severity ratings. Thus, the current design is sensitive to individual variation in responses to diverse moral stimuli. We explored whether activity in specific brain regions was positively correlated with moral severity ratings, and whether these regions differed for males and females. The primary hypothesis was that females would show a greater positive modulation of moral severity ratings by activity in the posterior cingulate, anterior insula, and dorsal anterior cingulate during moral picture viewing relative to males. In addition, we hypothesized that males would show a greater positive modulation of moral severity ratings by activity in posterior superior temporal sulcus during moral picture viewing relative to females. Whether we would observe gender differences in other neural correlates of moral processing, such as medial prefrontal cortex, was an open question.