Toward a cross-species understanding of empathy

Abstract

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.

Keywords: affective neuroscience; anterior cingulate cortex; contagion; emotion; reciprocity; rodent; social behavior.

Figure I

Nested hierarchies of control within the brain. A summary of circular, bottom-up and top-down causation by which lower BrainMind functions (e.g., primal emotional systems) are integrated, through bottom-up control, with higher-order MindBrain functions that then provide top-down regulatory control. Primary processes are shown as red squares, secondary process learning as green circles, and tertiary processes as blue rectangles (adapted from [33]).

Figure 1

Experimental approaches for assessing primal empathy in laboratory rodents. Nearly all of the studies that tap into some aspect of empathy processing in rodents utilize a painful sensory experience that can result in fear. As outlined in this cartoon depiction, the general approach entails presenting a noxious stimulus (often a shock) to a ‘target’, while an ‘observer’ witnesses this experience. Measures of behavioral responsiveness in an observer occur during the actual experience, or subsequently when a conditioned stimulus (CS) is presented, or when the target expresses a conditioned response (CR) to the CS. For example, (A) mice increase responsiveness to a painful unconditioned stimulus (US) when a familiar conspecific is concurrently exposed [62]. (B) Rodents increase freezing or express correlated freezing responses when observing a conspecific receiving a US [38,41,61]. (C) Prior social interaction coupled with a subeffective dose of morphine produces thermal analgesia [92], whereas observing a social partner in pain also produces subsequent thermal analgesia [62]. (D) Observing a non-fearful conspecific within a context reduces subsequent acquisition of contextual fear [63]. (E) The presence of a non-fearful social partner reduces retrieval of a fearful memory [67]. (F) Social interaction with a fear-conditioned conspecific increases subsequent acquisition of fear [66]. (G) Experienced rats respond to a CR of fear in others with increased freezing behavior [41]. (H) The CR of a partner rat is also sufficient to engender subsequent freezing in an observer [68]. (I) Mice acquire learned fear and avoidance responses after observing others being conditioned [39,41,69]. Not illustrated above are studies that have explored the role of social factors in fear-extinction (e.g., [64,65]).