The expression of emotion is limited in intensity and scope in boys and men relative to girls and women (Buck, 1977). Boys, but not girls, follow a developmental trajectory in which they increasingly inhibit facial expressions of emotion with age (Buck, 1977). In adulthood, men experience their emotions as less intense than women, particularly negative emotions, regardless of whether their emotional experience is measured via standardized self-report, behavioral observation, or physiological measurement (Bradley, Codispoti, Sabatinelli, & Lang, 2001; Schulte-Ruther, Markowitsch, Shah, Fink, & Piefke, 2008; Vrana & Rollock, 2002). They also require more intense stimuli to produce an emotional response, relative to women (Li et al., 2008). Men’s reactions to the emotional states experienced by another, i.e., empathy, may also be less intense than that experienced by women, although the methodology utilized may affect results. Empathy can be divided into two constructs, cognitive (Piaget, 1932) and affective empathy (Eisenberg & Miller, 1987). Cognitive empathy refers to the ability to understand the intentions and desires of another. Affective empathy refers to a more emotional and experiential level of empathy in which one literally feels the emotions experienced by another. While boys are not as strong as girls in either of these two skills, the gap is wider for affective empathy (Mestre, Samper, Frias, & Tur, 2009). On the other hand, recent findings indicate that while men rate themselves as less empathic than women (i.e., a subjective measurement), they may actually possess similar levels of empathy as defined by emotion recognition, perspective taking, and affective responsiveness (i.e., objective measurements; Derntl et al., 2010). Such results reveal the difficulties in measuring empathy. Self-reports are subject to social desirability, and gender differences are smaller for indices that are less self-evident regarding the skill being measured (Eisenberg & Lemaon, 1983).

Nonetheless, this relative lack of emotional experience and expression in men compared to women may be associated with sexually dimorphic patterns of psychopathology. If men tend to experience emotions less intensely, it should not be surprising that they are less susceptible to specific forms of psychopathology, such as depression (Marcus et al., 2005). This relative constriction in emotional intensity might also help to explain why, in comparison with women with depression, men with depression experience less symptom recurrence, milder comorbid affective and neurocognitive symptoms, and less perceptual biases towards negative stimuli (Barry, Allore, Guo, Bruce, & Gill, 2008; Bos et al., 2005; Marcus et al., 2005; Sarosi, 2011). This hypothesis is corroborated by hormonal data showing that in depressed samples, men do not respond as strongly as women to stimuli that are only moderately negative, as reflected by a less intense stress-related cortisol response, and by less difference in cortisol levels in recurrent versus non-recurrent depression (Bos et al., 2005; Peeters, Nicholson, & Berkhof, 2003). A similar hypothesis might be applied to bipolar disorder. While bipolar disorder is thought to have a more obvious genetic/physiological etiology than unipolar depression, it is nonetheless theorized that psychosocial stressors may trigger the onset of subsequent episodes of bipolar depression (Cohen, Hammen, Henry, & Daley, 2004). Thus, the lesser intensity of emotional experience in men may also serve as a buffer against these initial or future depressive episodes. In fact, compared to women with bipolar disorder, men are less likely to suffer from depressive symptoms, rapid cycling, or more severe forms of psychosis (Braunig, Sarkar, Effenberger, Schoofs, & Kruger, 2009; Curtis, 2005). Interestingly, men with bipolar disorder report lower levels of masculinity than those without the disorder (Sajatovic, Micula-Gondek, Tatsuoka, & Bialko, 2011), further evidence for a female susceptibility to affective disorders, one that is perhaps based on gender schema.

Men are also less susceptible to specific anxiety disorders, particularly panic disorder with agoraphobia. Again, the less expansive nature of emotional experience and expression in men may serve as a protective factor against anxiety, as men show lower normative levels of worry and rumination (Nolen-Hoeksema, 1991; Robichaud, Dugas, & Conway, 2003). Similar to what is observed in bipolar disorder, there is an association between lower levels of masculinity and greater levels of experienced psychopathology, in this, case social anxiety (Moscovitch, Hofmann, & Litz, 2005), suggesting that a less masculine gender role, or a more feminine gender role, may predispose one to anxiety.

Not only are the experiential and expressive aspects of emotion less intense in men relative to women, but men also possess a relative weakness compared to women in another area with important implications for psychological functioning and wellness, social cognition (Hall & Matsumoto, 2004; Hampson, van Anders, & Mullin, 2006). Social cognition refers to cognitive skills that enable the understanding of another’s thoughts and feelings (Brothers, 1990). In various domains of social cognition, men perform worse than women throughout their lifespan (Hu, Chan, & McAlonan, 2010; Lee et al., 2013; Walker, 2005). While recent data with more precise methodology have raised questions about the consistency of these findings, when a sex-linked strength in social cognition exists, it is often in a direction that favors girls/women, relative to boys/men (Hall & Matsumoto, 2004; Hampson et al., 2006; Montagne, Kessels, Frigerio, de Haan, & Perrett, 2005; Rehnman & Herlitz, 2007). Additionally, the functional neuroanatomical basis of social competence differs across the sexes. While the social brain, a reference to the neural networks needed for social perception, may be similar across gender, how and when these networks are utilized, and to what extent they are utilized in a manner towards achieving positive social outcomes, appear to differ in a sexually dimorphic manner (Koch et al., 2007).

One area of social cognition that has received much study is the processing of facial stimuli. Sex differences in the processing of facial stimuli are evident quite early in development. At five years of age, boys exhibit a level of facial emotion decoding that girls possess more than a year and a half earlier (Boyatzis, Chazan, & Ting, 1993). These findings are not unequivocal, and may vary depending upon methodology and task parameters. For instance, girls from 7 to 13 years of age displayed greater speed in processing facial information but also compromised accuracy (Rosenberg-Kima & Sadeh, 2010). Regardless, the weight of the evidence suggests that boys and men are simply not as skilled as girls and women in recognizing, recalling, or labeling emotions in facial expressions (Hall & Matsumoto, 2004; Hampson et al., 2006; Montagne et al., 2005; Rehnman & Herlitz, 2007), and tend to rate emotions expressed in faces as less intense (Biele & Grabowska, 2006; Knyazev, Bocharov, Slobodskaya, & Ryabichenko, 2008). There is also a subgroup of men with specific deficits in the processing of certain facial expressions, deficits that are as severe as those observed in cases of damage to the amygdala (Corden, Critchley, Skuse, & Dolan, 2006). Interestingly, the female advantage for facial processing is reduced when faces are inverted (McBain, Norton, & Chen, 2009). This suggests a possible bias towards local feature processing of faces in men, a somewhat unexpected finding given reports showing a more piecemeal approach to spatial cognition tasks in women relative to men (Roalf, Lowery, & Turetsky, 2006). On the other hand, it is suggestive of findings in individuals with autism spectrum disorders (ASD). In ASD, there is a piecemeal approach to facial processing that results in deficits compared to typically developing peers, deficits which are eliminated when faces are presented upside-down (Tantam, Monaghan, Nicholson, & Stirling, 1989). Thus in men, it is possible that social stimuli represent a unique category of stimuli to which typical rules of cognitive processing may not apply.

The relative weakness men possess in perceiving emotions is not limited to the perception of emotional stimuli in faces. Theory of mind is a broader construct which refers to the ability to attribute mental states to oneself and to others, and to recognize that the mental states of others (e.g., beliefs, desires) may differ from one’s own. By three years of age, boys lag behind girls on tasks measuring theory of mind (Walker, 2005), and continue to lag behind girls throughout later childhood and early adolescence (Calero, Salles, Semelman, & Sigman, 2013; Hu et al., 2010). In adulthood, men have other difficulties in social perception relative to women, such as in reading nonverbal cues in body language, although these difficulties vary with the emotion expressed (Sokolov, Kruger, Enck, Krageloh-Mann, & Pavlova, 2011). Men also have relative difficulties differentiating friendliness from sexual interest and vice versa (Farris, Treat, Viken, & McFall, 2008).

Not only do men show weaknesses relative to women in specific social cognitive skills, but they also display less interest in social situations, a finding evident developmentally from a very early age. That is, in the days following birth, male infants show less eye contact than female infants (Geary, 2002), and prefer to look at toys rather than faces, whereas the opposite pattern is observed in female infants (Connellan, Baron-Cohen, Wheelwright, Batju, & Ahluwalia, 2000). Interestingly, women also tend to view themselves through a more social lens than do men (Cross & Madson, 1997). Markus and Kitayama (1991) discussed self-construals as the ways in which individuals perceive themselves and their larger role in society. They applied this construct to a comparison of eastern and western cultures. Individuals from eastern cultures construe the self as inseparable from society at large, resulting in an interdependent self-construal. In contrast, individuals from western cultures perceive themselves as separate from their broader social context, and therefore, as more autonomous, resulting in an independent self-construal. These concepts have been studied across gender and results reveal that women are more likely to develop interdependent self-construals while men are more likely to develop independent self-construals (Cross & Madson, 1997).

The relative deficits in social cognition, the greater interest in non-social stimuli, and the tendency to possess a more independent self-construal, all evident in men relative to women, may have implications for gender-specific findings in the field of psychopathology. Attention has been given to the manner in which specific forms of psychopathology, such as depression, lead to social isolation, which subsequently serves to reinforce pathological thoughts and behaviors (e.g., Coyne, 1976). Conversely, little attention has been given to the ways in which the lack of a social bias might also serve as a buffer against specific manifestations of psychopathology. For instance, men, relative to women, may be less likely to come into contact with others with personal problems because they are less socially oriented. Furthermore, if affective empathy in men is somewhat unrefined, they may be less likely to internalize the problems of others in their immediate social circles (Schuster, Kessler, & Aseltine, 1990). Similar findings may apply to anxiety. For instance, women but not men show salivary cortisol increases during a social isolation task (Stroud, Salovey, & Epel, 2002). The sexually dimorphic response to acute threat has led to a revision of the fight-or-flight hypothesis describing reactions to acute stress. That is, facing an acute threat, men may utilize aggression or fear, respectively, to directly confront or flee from the threat. However, the tendency of women to affiliate with, and nurture others, has led some to suggest that women possess a tend and befriend reaction to such stress (Taylor et al., 2000). Theoretically, the fight-or-flight response typically exhibited by men might lead to a discharge of potentially dysphoric feelings, and thus, a subsequent resolution of sensations of anxiety, whereas in women, their tendency to affiliate and nurture might result in residual anxiety and no immediate resolution of dysphoria.

In contrast to what may be observed in depression and anxiety, the absence of a social bias has negative connotations in other disorders and characterological pathologies such as schizophrenia and sociopathy. This is the case irrespective of whether a non-social orientation is a risk factor for the psychopathology, a potential agent for symptom exacerbation, or simply a manifestation of underlying psychopathology. For example, in schizophrenia, men exhibit greater difficulty with social intimacy (Mulligan & Lavender, 2010) and greater deficits in social cognition (Van’t Wout et al., 2007). These findings are important because social withdrawal is characterized as a negative symptom of schizophrenia, and negative symptoms have greater predictive power for functional outcomes than do positive symptoms such as hallucinations (Rabinowitz et al., 2012). This may be one reason why men with schizophrenia tend to have worse functional outcomes than women (Seeman, 1986). Deficits in other aspects of social cognition, specifically empathy, are the defining features of other forms of psychopathology dominated by males, such as ASD and sociopathy. Thus, in one report, in males, but not females, the antisocial behavior observed in Conduct Disorder and Antisocial Personality Disorder was directly correlated with an inability to subjectively experience the emotions of others (Dadds et al., 2009).

The neuroanatomical correlates of emotional experience differ in men and women (see Semrud-Clikeman and Robillard in this volume), with effect sizes that are comparable to those found in other areas of neuroscience research (Cahill, 2006). Compared to women, men show a less intense degree of neural activation to emotion-provoking stimuli (Schirmer, Zysset, Kotz, & Yves von Cramon, 2004), although as in behavioral studies, some of this is modulated by the specific emotion elicited (Wrase et al., 2003) (e.g., men tend to exhibit a greater degree of activation to pleasant pictures than do women; Sabattineli, Flaisch, Bradley, Fitzsimmons, & Lang, 2004; Wrase et al., 2003). Broad findings include a greater degree of lateralization in men relative to women during emotional perception (Killgore & Yurgelun-Todd, 2001). There are also regional differences. In a study by Lee, Liu, Chan, Fang, and Gao (2005), men consistently activated the right insula and left thalamus, whereas women’s activation patterns differed depending upon the emotion induced. Based on data showing that insular activation is associated with the induction of internal emotions, and based upon their own analysis of cognitive processes reported by participants during the task, the results were interpreted by the authors to suggest that men relied upon past emotional experiences when perceiving emotions in pictures or scenes, whereas women were able to engage brain structures responsible for emotion more directly.

Sex-linked divergence in neural activation patterns occurs with stimuli of mild intensity that are likely to induce only modest shifts in mood, if any at all. For instance, during performance of a working memory task, presentation of noxious stimuli in the form of particularly strong and unpleasant odors compromised performance across genders but did not change the neural activation patterns in men (Koch et al., 2007), which remained centered on areas associated with working memory, specifically prefrontal and parietal regions. However, in women, the same condition resulted in significantly stronger activation in brain regions responsible for processing emotion, such as the amygdala and orbitofrontal cortex. Similarly, when perceiving humor, activation patterns in women centered on a ventral limbic system directly connected with emotions, such as the amygdala, insula, and anterior cingulate cortex (Kohn, Kellermann, Gur, Schneider, & Habel, 2011). In contrast, men undergoing this task also displayed activation of a dorsal system associated with a greater degree of cognitive evaluation of the humorous stimuli. In a study by Yuan et al. (2009), both men and women displayed electrophysiological responses indicating a similar degree of conscious emotional processing of particularly negative images. However, men, but not women, lacked this electrophysiological response when viewing stimuli that were only moderately unpleasant. These results may be identifying the electrophysiological basis in the brain for the susceptibility to depression, which is thought to increase with increased exposure to relatively minor daily hassles. There also appears to be a sexually dimorphic neuroanatomical basis to the regulation of emotions. In men, conscious regulation of emotion results in lower activation in the amygdala compared to women (McRae, Ochsner, Mauss, Gabrieli, & Gross, 2008). These findings in sum appear to suggest a neuroanatomical etiology for why men are less susceptible to the emotional influences of stimuli that either lack an obvious emotional component, or whose emotional relevance is minor at best. Perhaps as a result, when attempting to regulate their emotions, men show less need for brain structures associated with emotional processing.

Sex-linked differences in neural activation have been observed during completion of empathy tasks. These differences provide some clues to the underlying thought processes in men and women concerning empathy, and further suggest that men experience lower levels of empathy. For instance, in one study, when led to believe that an unfairly behaving confederate was receiving an electric shock, female participants displayed empathy-associated activation in pain-related neural regions (i.e., fronto-insular and anterior cingulate cortices), while men showed activation in brain regions associated with reward, such as the nucleus accumbens and orbitofrontal cortex (Singer et al., 2006). Men and women react differently when playing a gambling game that results in monetary gain for themselves at the expense of monetary loss for a confederate. Women, but not men, display a medial frontal negativity component on an event-related potential, which is thought to reflect emotional categorization (Fukushima & Hiraki, 2006). Thus, even when benefitting from this outcome, women still display evidence of an emotional reaction whereas men do not.

One neural network candidate for empathy that may differ in men and women is the mirror neuron system. The mirror neuron system is a network of brain areas that becomes activated when watching another execute an action, in a regionally specific manner that correlates with the region that would be activated if the individual themselves executed the action. Based upon these findings, researchers have suggested that this system may help form a foundation for the neural basis of social cognition and empathy (see Preston & de Waal, 2002 for a review). Studies have shown differences in the pattern and intensity of neuroanatomical activity in men relative to women on tasks designed to provide behavioral correlates of this system. For instance, men relative to women show considerably less suppression of the mμ EEG rhythm when watching hand actions but this difference does not occur when the stimulus is a moving dot (Cheng et al., 2008). The mμ rhythm results from firing of sensorimotor neurons in synchrony. However, when an individual executes an action or watches another do the same, the firing becomes asynchronous and as a result the mμ rhythm is suppressed. This suppression that occurs when observing others is theorized to reflect one component of the mirror neuron system (Hari et al., 1998). Interestingly, mu suppression in the study by Cheng et al. (2008) positively correlated with a self-report measure of interpersonal distress, and negatively with a measure of systemizing tendencies. These findings suggest electrophysiological correlates of the extreme male brain theory of autism, in which men show less understanding and subjective experience of the intentions and emotions of others. Another report found that compared to women, men also showed less activation of mirror neuron system components (i.e., right inferior frontal cortex and superior temporal sulcus) when processing their own emotional expressions, while there was increased neural activity in the left temporoparietal junction in males (Schulte-Ruther et al., 2008). Furthermore, when the activation pattern that occurs during the perception of one’s own emotions is contrasted to the activation pattern that occurs during the perception of the emotions of another, only women show a difference (Schulte-Ruther et al., 2008). Thus, there are clear distinctions across the sexes in the neuroanatomical and neurophysiological basis for empathy which may contribute to sex-linked differences in behavior.

There are temporal differences in emotional processing and empathy between the sexes which have been demonstrated in electrophysiological studies. Men have been shown to possess a bias towards a pre-cognitive processing stage correlating with coarse analysis, whereas women have been shown to display a bias towards a later and more cognitive stage of processing focused on fine-grained stimulus analysis (Knyazev, Slobodskoj-Plusnin, & Bocharov, 2010). Thus, while both men and women become consciously aware and capable of cognitive processing of stimuli at equal points in time following stimulus presentation, women apparently give greater attention to stimuli at a conscious level, particularly with emotional stimuli. This may be why under certain experimental conditions, women’s P300, the portion of an evoked potential considered to reflect cognitive activity, is modulated by emotional context to a greater extent than men’s (Garcia-Garcia, Dominguez-Borras, SanMiguel, & Escera, 2008). Emotional contagion studies reveal similar results. Emotional contagion refers to a form of empathy that is behaviorally similar to what is theorized to occur neuroanatomically via the mirror neuron system. When observing the emotional state of others, such as manifested in a facial expression, an individual begins to subjectively experience the emotion represented by that expression. In one report, when stimuli were displayed for 23 ms, a duration short enough that no conscious cognitive processing is possible, no differences in responses to emotional stimuli were observed across the sexes on either the basis of verbal report or objective measurement of facial musculature (i.e., electromyography) (Sonnby-Borgstrom, Jonsson, & Svensson, 2008). At longer exposure times, however, women reported a greater degree of emotional contagion whereas men did not. Thus, electrophysiological data suggest that men, compared to women, may process some stimuli more rapidly, but in a coarse manner that does not lend itself well to the sophisticated analysis that emotional perception requires.

In summary, there are sex-linked differences in the intensity, latency, and location of neuroanatomical responses to emotion-provoking stimuli. However, the manner in which neuroanatomical divergence in emotional expression and emotional perception develops is unknown. Do societal influences lead to sexual dimorphisms in brain functioning? The social adjustment of girls but not boys is related to their emotional recognition accuracy, suggesting this property is more valued in girls (Leppanen & Hietanen, 2001). However, hormonal differences may also contribute to these sexual dimorphisms. When faced with threat-related stimuli, both behavioral responses and responses of the amygdala are correlated with testosterone level in men (Derntl et al., 2009). Thus, societal influences, biological factors, and, potentially, genetic factors, may all interact to facilitate these sex-linked differences in emotional processes in a way that is not yet fully understood. The fact that these sexual dimorphisms are relative and not absolute complicates interpretation of the findings, as there is no definitive evidence suggestive of a social brain that is uniquely and completely male or female.