The present study yields several new insights into the role of social understanding and alexithymia for aggressive behaviour. Firstly, men with a history of aggressive behaviour showed decreased sharing of negative affect with others, indicating diminished empathy, and reduced compassion after emotionally negative videos. Secondly, no ToM deficit was found, demonstrating intact cognitive perspective-taking in men with a history of aggressive behaviour. These results were observed both when comparing men with and without a history of aggressive behaviour and when correlating aggression severity with empathy, compassion and ToM. Thirdly, the empathy deficit in men with a history of aggressive behaviour was mediated by increased alexithymia.

The results of the present study confirm the hypothesised link between aggression and impaired social understanding, showing that it is a deficit in feeling another person’s pain, but not the reasoning about their motives, intentions, and goals, that allows crossing personal boundaries and inflicting bodily harm. Thus, the present data clarify the on-going questions of whether and how aggression relates to impaired social understanding. While previous meta-analyses yielded largely inconsistent evidence22, 24, the clear results observed here speak for an experimental operationalization of social understanding, which, in contrast to the mostly applied questionnaire assessments, is not subject to response tendencies, for example related to social desirability. It also seems critical to test the different aspects of social understanding within the same individuals to allow conclusions about their specific impairment. Lastly, replicating group differences with correlational data validates the observed relationships as suggested by Vachon et al.24 and by Mariano et al.43.

The observed deficit in healthy men with a history of aggressive behaviour in affective social understanding is in line with evidence from psychopathology. For instance, psychopathy, which is characterised by severe antisocial behaviour, has been related to reduced empathic responses, while Theory of Mind performance is not affected44,45,46,47,48,49. A similar pattern has been reported in patients with narcissistic personality disorder, who also show reduced prosocial behaviour50, 51. A primary lack of empathy and compassion is also found in frontotemporal dementia and, more generally, the frontal lobe syndrome. Paralleling our present findings, studies of these conditions reported a lack of empathy and compassion associated with elevated levels of aggressive behaviour52,53,54,55,56.

Violent behaviour toward others and themselves has also been reported in some patients with autism spectrum disorder57, 58, which is mainly associated with deficits in ToM, but not empathy37, 59, 60. However, prevalence for alexithymia is largely increased in autism and can lead to reduced empathic responses in autistic individuals as well31, thus raising the question of whether the aggressive behaviour is primarily associated with the ToM deficits or rather alexithymia37. The present findings highlight that the relationship between lack of empathy and aggressive behaviour is not confined to people with psychiatric disorders but is also crucial in understanding aggression in healthy individuals, such as criminal offenders.

In line with our findings, recent studies reported that criminal offenders had no deficits in judging other people’s behaviour as right or wrong – possibly indicating intact ToM – but had deficits in sharing the suffering of other people43, as well as deficits in emotion recognition and empathy in ecological, context-sensitive measures61.

Our findings are also in line with investigations that link enhanced social understanding to prosocial behaviour4, 23, 62, 63, 64 possibly through enhanced early detection of others’ emotions13, 20. While the specific and relative contributions of empathy, compassion and ToM to prosocial behaviour are not yet entirely clear, some first evidence demonstrated that training in compassion-focused meditation can increase helping and non-selfish behaviour in interactive game paradigms65, 66. This may be an avenue for future intervention studies in chronically aggressive individuals.

Alexithymia has already been shown to play an important role in empathic responses, which was replicated in this study28, 36, 38, 39, 67. In General, alexithymia, as the ability to empathise with other people’s emotional states relies on parts of those networks that are involved when the emotional states are experienced by oneself, difficulties in identifying one’s own feelings seem to be paralleled by reduced empathy31. The present findings suggest that the empathy deficit in men with a history of aggressive behaviour is mediated by increased alexithymia, suggesting that it may actually be aberrant alexithymia that brings about reduced empathic responses. Further suggestions for the relation of alexithymia to aggression have been made by Zillmann68, assuming that monitoring one’s own level of excitement is crucial for leaving dangerous situations, which people with high levels of alexithymia may consequently be unable to do69. Furthermore, awareness of one’s own emotions is correlated with tolerating negative emotions70, and a reduced capacity to identify emotions results in more maladaptive coping-styles71, 72. Training emotional awareness may, therefore, be another promising approach in psychotherapeutic intervention.

There are some limitations to the present study. On average the group of men with history of aggressive behaviour scored lower on all measures of education and intelligence. When years of education and verbal IQ were used as covariates in our analyses, the results of the group-by-valence interaction and the group difference in the negative valence condition remained largely the same, while the mediating effect of alexithymia on empathic responding did not remain significant. It is thus acknowledged that we cannot fully exclude that differences in education and IQ may play a role and that future studies in groups matched for education and IQ will have to replicate the present findings. In line with conceptual considerations, the present data did, however, not reveal a correlation between empathy measures and years of education or IQ nor between compassion measures and years of education or IQ, when the two groups were analysed separately (see Supplement S8). Thus, empathy and compassion and the deficits therein observed in the group of men with a history of aggressive behaviour seem not to be linked with education and intelligence. In contrast, one may rather have expected differences in education and IQ to affect performance in ToM73. Strikingly, we found no group difference in ToM measures, suggesting again that, in the present study, group differences do not simply and unspecifically occur due to differences in education and intelligence74.

A second point concerns the ratings in the EmpaToM, which are still subjective in nature. However, the EmpaToM ratings have previously been shown to directly trace neural responses in empathy related brain regions on a trial-wise level and also correspond to changes in heart rate20. Future studies in aggression should, nevertheless, include more of such objective measures, in particular to elucidate the influence of differences in alexithymia on subjective and objective affective social understanding. Despite the exclusion of DSM-IV Axis I and II disorders, psychopathy67 and other inter-individual difference characteristics such as cognitive schemata and scripts75, 76 were not assessed. Future research should include such measures to test the specific relations to aggressive behaviour. Lastly, we only tested aggression in men. While the prevalence for physical aggression, in particular, is much lower in women77, it still remains to be tested whether the same mechanisms observed here can be generalised to women.

To conclude, based on the finding that affective and cognitive routes to understanding others are distinct and can be assessed separately20, we investigated the role that deficits in these social functions play for aggressive behaviour. We observed a selective deficit in affective responses, but not cognitive perspective-taking, in men with a history of aggressive behaviour, which suggests that it is the sharing of others’ emotions and feeling for them, that inhibit aggression. Deficits in cognitive understanding of others’ mental states, however, do not play a critical role for aggressive behaviour. Selectivity of the impairment also corroborates the separation of affective and cognitive routes to social understanding. Furthermore, as alexithymia mediates reduced empathic responses in men with a history of aggressive behaviour, the present results underline the importance of awareness of one’s own emotions for affect sharing and allow suggestions for future developments in psychotherapeutic treatment to include emotional awareness training.