The present work revolves around the phenomena and neural mechanisms underlying the human capability to empathize with others’ pain. It will be shown that observing or imaging others’ pain brings about the activation of neural structures largely overlapping with those activated during the experience of pain on oneself and that neural structures involved in both emotional and sensorimotor processing may be recruited during empathy for pain.

Empathy enables us to share the emotions and the sensations of others. Although empathy has long attracted the interest of psychologists and philosophers, only recently has this subject attracted neuroscientists. Current neuroscientific model of empathy states that the observation or imagination of another person in a particular mental state automatically activates a representation of that state in the observer (Preston, de Waal, 2002; Decety, Jackson, 2004; Avenanti, Aglioti, 2006). Recent studies support this resonant view of empathy by providing evidence for common neural modulations elicited when experiencing disgust, touch or pain in oneself, and when perceiving the same feelings in others (Gallese et al. 2004). These empathic “mirror” responses to the observation of others’ feelings may be related to the covert simulation of different somatomotor and emotional aspects of others’ experience.

Pain is a complex subjective feeling with sensory-discriminative (e.g. intensity, duration, localization of the noxious stimulus) and affective-motivational (e.g. unpleasantness) components. These different components are mapped in two partially separate nodes of a complex neural network referred to as the “pain matrix”. Converging lines of evidence indicate that the sensory dimension of pain is mainly coded in sensorimotor neural structures, while the affective component is mapped in several limbic areas including the anterior cingulate cortex (ACC) and the anterior insula (AI) (Peyron et al. 2000; Rainville, 2002). The neural segregation of sensory and affective components makes pain an interesting model for testing theories of empathy based on the notion of resonant “mirror” mechanisms.

A number of studies have consistently demonstrated that observing or imaging others’ pain brings about the activation of the affective division of the pain matrix suggesting a sharing of emotional components of pain (Singer et al. 2006; Saarela et al. 2006). The findings that ACC and AI activity during empathy for pain may be modulated by the type of emotional bond between individuals (Singer et al. 2006) or by specific emotional traits of the onlooker’s personality (Singer et al. 2006; Saarela et al. 2006) further hints at the affective nature of these neural responses to others’ pain.

To what extent do we share others’ pain? Do we share only the affective dimensions of pain? In a series of transcranial magnetic stimulation (TMS), somatosensory-evoked potentials (SEPs) and laser-evoked potentials (LEPs) studies, we provided evidence that empathy for pain may imply also the sharing of fine-grained somatomotor representations (Avenanti et al. 2005; Bufalari et al. 2007). We demonstrated that the direct observation of painful stimuli delivered to specific body parts of a human model brings about a suppression of corticospinal excitability similar to what found in subjects who actually received painful stimulations (Avenanti et al. 2005). These inhibitory cortico-spinal responses are specific to the body part the subjects observed being stimulated and correlate with the intensity (but not the unpleasantness) of the pain ascribed to the model, and thus likely reflect the simulation of basic sensory features of others’ pain (intensity, localization of pain) (Avenanti et al. 2005). In a similar vein, the direct observation of others’ pain may modulate specific components of somatic (SEPs) and nociceptive (LEPs) processing thus suggesting that somatosensory cortices may be crucial not only in pain perception but also in extracting sensory qualities of others’ pain (Bufalari et al. 2007).

Taken together, neuroimaging and neurophysiological studies suggest that our ability to empathize with the pain of others’ relies on neuronal systems that underpin our own both bodily and emotional states. It may be possible to think of at least two forms of empathy linked to one another in an evolutionary and developmental perspective. A comparatively simple form of empathy, based on somatic resonance, may be primarily concerned with mapping external stimuli onto one’s own body (Avenanti et al. 2005; Bufalari et al. 2007). A more complex form of empathy, based on affective resonance, may deal with emotional sharing and with the evaluation of social bonds and interpersonal relations (Singer et al. 2006).

A direct matching of specific sensory features of others’ pain occurs in sensorimotor structures of the pain matrix (Avenanti et al. 2005; Bufalari et al. 2007), while emotional components of others’ painful experiences are encoded in the affective division of the network (Singer et al. 2006; Saarela et al. 2006). Hence, empathy for pain may take different forms in different nodes of the complex neural network that represents sensations, feelings and emotions linked to the experience of pain.

Philosophers have emphasized that our bodily sensations are intrinsically private. However, neuroscientific findings suggest that, at least in humans, the social dimension may extend even to the very basic, sensorimotor level of neural processing.