Trends in Neurosciences
ReviewToward a cross-species understanding of 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)
Section snippets
The vagaries of ‘empathic’ terminologies
The term ‘empathy’ continues to have a diverse as well as nebulous usage, with ‘sympathy’ and ‘compassion’ being perennial colloquialisms used to describe related phenomena. One must remember that the term is a recent contribution to the vernacular, emerging in the early 20th century from the Greek empatheia (from em- ‘in’ + pathos ‘feeling’) and translated into the German Einfühlung, namely ‘feeling into’, especially when humans aesthetically appreciate the beauty of art. The English version of
Evolutionary affective foundations of empathy: levels of analysis in the brain and mind
Clearly a detailed, constitutive understanding of the mechanisms of empathy must come from cross-species neuroscience. Given the many excellent reviews covering correlative human brain imaging of empathy 3, 11, 24, 25, 26, 27, we focus here on the primal emotional foundations of empathy in mammalian brains. The ‘primary-process’ emotional systems of the brain, which generate affective feelings (Box 2), are more accessible in animal models than in humans 23, 28. The interaction of primal
Beyond terminological and conceptual conundrums
A cross-species analysis readily synergizes with the original approach of Lipps, whereby empathy was characterized by how ‘the perception of an emotional gesture in another directly activates the same emotion in the perceiver, without any intervening labeling, associative or cognitive perspective-taking processes’ ([22], p. 2). As succinctly put by Hoffman [14], empathy is the process through which an individual generates an ‘affective response more appropriate to someone else's situation than
Top-down cognitive regulation of empathy
With maturation, guided by the affective qualities of childhood [54], humans develop the thought-related cognitive functions that vary considerably among individuals, providing diverse top-down control over social relationships 33, 55. Obviously, much having to do with empathy among humans is cognitive and elaborated by higher brain functions (e.g., sense of fairness, sympathetic perspective-taking, and compassion). However, we need to consider how those higher functions developmentally arise
Primary-process empathy
In its most basic form, empathy may be an inherent property of primal emotional systems, reflecting the fact that there is perceptually induced resonance of the same affective states in nearby animals. This may take its most poignant form in the capacity of mothers to intrinsically understand the emotional feelings of their infants. For instance, PANIC networks engender separation calls to signal psychological distress (probably a form of psychic pain evolving from pre-existing systems that
Secondary-process modulation and parsing of primal empathy
It is not clear that secondary learning and memory processes contribute anything unique to the spectrum of primal empathic responses beyond parsing those responses in terms of space, time, and intensity. This level of brain processing appears to be completely unconscious 32, 48, with well-established circuits for emotional learning (especially fear-conditioning) operating without the addition of anything new in terms of subjective emotional experiences. Learning can both intensify and moderate
Tertiary processes: the social emotions writ large
These highest levels of psychological processing are best studied in humans. There is a vast literature on human empathy, with insufficient space here to add much of significance. However, this is where research on the neurochemistries of social bonding – first opioids and subsequently oxytocin – both of which reduce separation-induced PANIC robustly (reviewed in 23, 48), may engender differential predictions about empathy – opioids may reduce empathy by dampening experienced social pain
The social foundations of empathy
Modern neuroscience is beginning to provide tools to clarify how the evolutionary sources of empathy are deeply grounded in fundamental brain processes – not only in our capacity to experience physical pains but also in the emotional networks that make us socially interdependent creatures. Although empathy has different connotations for different people, most agree that it is deeply emotional and pro-social – whereby one responds to the bodily needs, pains, and psychological losses of others
Acknowledgments
J.B.P. was supported by a National Institutes of Health (NIH) training grant (F32 MH096475) during the writing of this paper.
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