Toward a cross-species understanding of empathy

Highlights

• Signs of empathy have been observed in many mammals, including laboratory rodents.

• ‘Primal empathy’ utilizes the seven basic emotional systems of the mammalian brain.

• Affective neuroscience approaches can elucidate the underlying brain substrates.

• Continued study of primal empathy in rodents will benefit mental health practices.

• A neuro-evolutionary paradigm can illuminate how empathy is expressed in humans.

Although signs of empathy have now been well documented in non-human primates, only during the past few years have systematic observations suggested that a primal form of empathy exists in rodents. Thus, the study of empathy in animals has started in earnest. Here we review recent studies indicating that rodents are able to share states of fear, and highlight how affective neuroscience approaches to the study of primary-process emotional systems can help to delineate how primal empathy is constituted in mammalian brains. Cross-species evolutionary approaches to understanding the neural circuitry of emotional ‘contagion’ or ‘resonance’ between nearby animals, together with the underlying neurochemistries, may help to clarify the origins of human empathy.

Introduction

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, 4, 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) [6]. 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 [7]. 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’ ([8], 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 [9] and Russian evolutionist Pyotr Kropotkin [10], 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, 14, 15. Concurrently, primatologists recognized signs of empathic sensitivities 16, 17 and now neuroscientists, inspired by classic early behavioral studies 18, 19, 20, are fashioning reliable simplified models to study the evolutionary roots of empathy (Box 1 and Figure 1)