nih | Empathy reflects the capacity of one animal to experience the emotional feelings of another, a process with many cognitive refinements in humans. Thus, investigators commonly distinguish between emotional and cognitive forms of empathy (see below) [1,2]. Studies of empathy make up a relatively new subdiscipline in neuroscience, with human brain imaging providing many correlates of relevant, higher psychological functions [3–5]. Neuroscience research on empathy in other animals has lagged far behind, but simplified animal behavior models based on emotional contagion, the presumed foundations of empathy, have been developed (Figure 1) . Our goal here is to summarize such novel empirical approaches for studying empathy in laboratory rats and mice, and to highlight an integrated neuro-evolutionary strategy for understanding human empathy.
Before proceeding, we consider the meteoric rise of neuro-empathy studies during the past few decades. The study of empathy was sparse in the biologically-oriented sciences of the 20th century until E.O. Wilson’s Sociobiology (1975), where constructs such as kin selection and reciprocal altruism were seen as major evolutionary explanations for individuals behaving unselfishly, even ‘altruistically’, toward others, provided that such behaviors supported the survival of one’s own genes . Indeed, in Descent of Man, Darwin suggested that ‘We are thus impelled to relieve the sufferings of another, in order that our own painful feelings may at the same time be relieved’ and ‘those communities which included the greatest number of the most sympathetic members would flourish best, and rear the greatest number of offspring’ (, p. 88). Thus, inspired by writings of philosophers such as John Stuart Mill and Adam Smith, together with American social psychologists such as William McDougall  and Russian evolutionist Pyotr Kropotkin , a prosocial perspective emerged in late 20th century suggesting that individuals might be constitutionally more cooperative and emotionally interdependent than previously considered.
By the late 1990s human brain imaging offered robust approaches for identifying brain regions aroused during emotional states, encouraging systematic neuropsychological studies of empathy [11,12] that have now yielded diverse affective, cognitive, and social neuroscience perspectives [1,13–15]. Concurrently, primatologists recognized signs of empathic sensitivities [16,17] and now neuroscientists, inspired by classic early behavioral studies [18–20], are fashioning reliable simplified models to study the evolutionary roots of empathy (Box 1 and Figure 1)