*Interestingly two key regions, the anterior insula and anterior cingulate cortex (ACC), involved in affective processing in general and empathy in particular have singularly evolved in apes and humans. Cytoarchitectonic work by Allman and colleagues [22] indicates that a population of large spindle neurons is uniquely found in the anterior insula and anterior cingulate of humanoid primates. Most notably, they reported a trenchant phylogenetic correlation, in that spindle cells are most numerous in aged humans, but progressively less numerous in children, gorillas, bonobos and chimpanzees, and nonexistent in macaque monkeys. Craig [23] recently suggested that these spindle neurons interconnect the most advanced portions of limbic sensory (anterior insula) and limbic motor (ACC) cortices, both ipsilaterally and contralaterally, which, in sharp contrast to the tightly interconnected and contiguous sensorimotor cortices, are situated physically far apart as a consequence of the pattern of evolutionary development of limbic cortices. Thus, the spindle neurons could enable fast, complex and highly integrated emotional behaviors. In support of this view, convergent functional imaging findings reveal that the anterior insula and the anterior cingulate cortices are conjointly activated during all human emotions. This, according to Craig [24], indicates that the limbic sensory representation of subjective "feelings" (in the anterior insula) and the limbic motor representation of volitional agency (in the anterior cingulate) together form the fundamental neuroanatomical basis for all human emotions, consistent with the definition of an emotion in humans as both a feeling and a motivation with concomitant autonomic sequelae
Individuals who are self-aware, as evidenced by being able to become the object of their own attention, experience a sense of psychological continuity over time and space [65]. It has been speculated that any organisms capable of self-recognition would have an introspective awareness of their own mental states and the ability to ascribe mental states to others [66]. A clear sense of self may have evolved to solve at least two kinds of adaptive problems: 1) the self is the repository of the social feedback one receives from others and, 2) it allows one to model and understand the internal, subjective worlds of others, making it easier to infer intentions and causes that lay behind observed behaviors, thus improving interaction efficacy [67]. Interestingly, the development of self and other mental state understanding is functionally linked to that of executive functions, i.e., the processes that serve to monitor and control thought and actions, including self-regulation, planning, cognitive flexibility, response inhibition, and resistance to interference [68]. There is increasingly clear evidence of a specific developmental link between the development of mentalizing and improved self-control at around the age of 4 [69]. The development of cognitive control is related to the maturation of the prefrontal cortex [70]. In addition, there is hard evidence that a region around the paracingulate sulcus in the medial prefrontal cortex plays a specific role in mentalizing. This region contains spindle cells, a class of large projection neurons found only in great apes and humans, which are thought to be involved in coordinating widely distributed neural activity involving emotion and cognition [71]. This region has been found to be reliably activated by mentalizing tasks of various cognitive difficulties, ranging from judging the emotion in another person's gaze, to detection of intention in simple dynamic animations, attribution of intention to cartoons characters, story comprehension, detection of social transgression, and appreciation of humor [72].
Thus human empathy cannot be described only as a simple resonance of affect between the self and other. Indeed, empathy is both about sharing and understanding the emotional state of others in relation to oneself. The capacity for two people to resonate with each other emotionally, prior to any cognitive understanding, is the basis for developing shared emotional meanings, but is not sufficient for empathy. Such an understanding goes beyond this reflex-like response. It involves an explicit representation of the subjectivity of the other and a minimal self-other distinction. Recent neuroimaging investigations of the perception of pain in others support such a view (e.g., [55,57,58,112]). Indeed, all these studies have shown that part of the neural network (including the anterior cingulate cortex and the anterior insula) mediating self-experienced pain is shared when empathizing or observing the pain in others, and also that non-overlapping aspects within these regions are specifically activated for the self or the other. This supports the idea that personal and vicarious experiences at some level differ physiologically [120] and result in qualitatively distinct responses. Finally, empathy also necessitates emotion regulation in which the ventral prefrontal cortex, with its strong connections with the limbic system, dorsolateral, and medial prefrontal areas, plays an important role.
We believe that a greater understanding of the underlying computational processes and their neural underpinnings can contribute to a better characterization of empathy disorders in psychopathology.