This work presents a critical review of the historical, theoretical, and neurobiological bases of the theory of moral emotions. Neuroimaging methods and protocols used to study the neural correlates of moral emotions and the analysis of the brain functions involved in their processing, permit the formulation of hypotheses that attempt to understand some emotional and cognitive processes related to moral emotions. One such hypothesis refers to a neuro-matrix involving sensory systems, brainstem-mediated physiological reactions and frontal brain regions processing the interaction between moral and emotional stimuli. Cross-cultural research on human facial expression has identified universal patterns to express basic emotions such as fear, anger, or happiness. Nevertheless, the experience of some emotions and their facial expressions are regulated by social and cultural mechanisms. This type of regulation is observed in moral emotions since they are linked to the interests or welfare either of society as a whole, or of persons other than the judge or agent. Two typical features that identify moral emotions are their typical elicitors and tendencies towards specific actions. The release of a moral emotion is the perception of implicit and explicit violations of social norms and stereotypes included in personal codes, attitudes, and beliefs. In turn, the actions ensuing from moral emotions are communal or prosocial, because they promote a benefit in others and/or in the social order. Although there is not a definitive taxonomy of moral emotions, four families of prosocial feelings are suggested: a) other-condem ning emotions (contempt, anger, disgust); b) self-conscious emotions (shame, embarrassment, guilt); c) other-suffering emotions (compassion); d) other-praising emotions (gratitude, awe, elevation). Such emotions are relevant to the concept of morality because this is a complex representation that includes models of prohibited actions, notions of good and bad, concepts of fairness, ideals of justice, or justifications of punitive actions. Moreover, the cognitive processes and behaviors involved in moral emotions are related to the theory of mind that refers the ability to represent the mental and emotional states of others, such as their thoughts, desires, beliefs, intentions, and knowledge. The neurobiological substrate of this capacity involves cerebral regions related to the experience of basic emotions, such as the amygdala and the cingulated cortex, and regions related to complex cognition and emotional-social contexts, such as the prefrontal cortex and the superior temporal sulcus. Neurobiological approaches to moral emotions have become relevant to study psychopathologies linked to antisocial behaviors, particularly the psychopathic or Antisocial Personality Disorder. Psychopaths show decreased emotional and physiological reactions to emotional stimuli and deficiencies to identify emotional expressions. However, they do not fail to represent or to infer others mental states or theory of mind. Therefore, the psychopathic disorder is not only linked to distortions in interpreting socially-learned moral values, but also to alterations of cognitive processes required to link the affective system to moral values. This assumption is supported by brain-imaging,studies demonstrating the involvement of areas associated to the processing of complex social stimulus and language, such as prefrontal cortex, orbitofrontal cortex, polar frontal cortex, and anterior temporal lobe in psychopathic patients. The affected-areas also include regions such as the amygdala, ventromedial hypothalamus, thalamus, and caudate nucleus involved in the experience or expression of emotions. Scientific publications directly referring to the neurobiological research of moral emotions and the evaluation of moral judgments occupy a period between 2001 and 2005. The neurobiology of moral emotions has evolved rapidly by the use neuro-imaging techniques such as Functional Magnetic Resonance Imaging (fMRI) and Positron Emission Tomography (PET). Brain images related to moral emotions are obtained by the use of moral stimuli in three types of situations: (a) while subjects resolve cognitive tasks, for example, reading moral emotional statements, (b) during passive or instructed viewing of affective pictures, or (c) during the resolution of moral dilemmas. The brain areas that become significantly active during these tasks provide a neurobiological interpretation of the mental operations involved in moral emotions. Thus, the medial frontal gyrus is activated during the elaborate personal and impersonal moral judgments produced by viewing moral pictures, attributing intentionality of movement, processing of facial expressions, and during the attribution of mental states (theory of mind). The posterior cingulated, restrosplenial, and precuneus cortex are associated with the elaboration of moral judgments elicited by viewing moral pictures and theory of mind. The superior temporal sulcus and the parietal lobe are related with moral judgments while viewing moral and emotional pictures and films, and attributing intentional movements. The superior temporal sulcus is also associated with the processing of social contexts. Orbitofronal and ventromedial frontal cortex is associated with the processing of simple moral judgments while viewing moral pictures, the evaluation of emotionally-charged social events, during empathy and attribution. The temporal pole is also associated with theory of mind, the elaboration of simple moral judgments and with the recalling of emotional situations. The amygdala is activated during the processing of moral pictures and social events based on facial expressions. Other empirical investigations involving a moral interpretation of data such as studies of general emotions, empathy, theory of mind, neurological disorders, and antisocial behavior, are also relevant to understand the brain activation patterns associated to cognitive and emotional social functions. Working models of psychopathologies that manifest antisocial behaviors are also required to interpret neuroimaging data. Meta-analyses of human behavior and proto-moral behavior in non-human species related to the elaboration of moral judgments and emotions are also relevant for the same purpose. Finally, moral emotion research requires the elaboration of accurate protocols based on psychological approaches directed to elicit particular moral emotions which enable the definition and neural substrates of its specific qualities.
