Rodent empathy and affective neuroscience

Abstract

In the past few years, several experimental studies have suggested that empathy occurs in the social lives of rodents. Thus, rodent behavioral models can now be developed to elucidate the mechanistic substrates of empathy at levels that have heretofore been unavailable. For example, the finding that mice from certain inbred strains express behavioral and physiological responses to conspecific distress, while others do not, underscores that the genetic underpinnings of empathy are specifiable and that they could be harnessed to develop new therapies for human psychosocial impairments. However, the advent of rodent models of empathy is met at the outset with a number of theoretical and semantic problems that are similar to those previously confronted by studies of empathy in humans. The distinct underlying components of empathy must be differentiated from one another and from lay usage of the term. The primary goal of this paper is to review a set of seminal studies that are directly relevant to developing a concept of empathy in rodents. We first consider some of the psychological phenomena that have been associated with empathy, and within this context, we consider the component processes, or endophenotypes of rodent empathy. We then review a series of recent experimental studies that demonstrate the capability of rodents to detect and respond to the affective state of their social partners. We focus primarily on experiments that examine how rodents share affective experiences of fear, but we also highlight how similar types of experimental paradigms can be utilized to evaluate the possibility that rodents share positive affective experiences. Taken together, these studies were inspired by Jaak Panksepp's theory that all mammals are capable of felt affective experiences.

Figure 1

Conditioning apparatus to assess social transfer of fear among mice. Mice are habituated to the apparatus and then an observer (left) is exposed to a demonstrator (right) receiving 10 consecutive forward-pairings of a 30-sec tone and a 2-sec shock (90-sec inter-trial interval). After 2 days of conditioning, the observer is placed on the side of the apparatus where the demonstrator was conditioned and it is then exposed to 5 presentations of the CS-only followed by 5 presentations of the CS-UCS contingency. The steel bars on the demonstrator side of the apparatus deliver electrical current whereas the bars on the observer side are inactive. Conditioning and testing are conducted during the dark phase of the circadian cycle under dim red illumination.

Figure 2

Freezing behavior of mice. (a) Without conditioning or observations of fearful demonstrators, mice from both the BALB and B6 genetic backgrounds expressed minimal freezing responses to the tone. Freezing was measured for 30 sec during each CS presentation. (b) B6 mice expressed more freezing behavior than BALB mice to the CS if they had prior experience with fearful demonstrators. Freezing was measured for 30 sec during each CS presentation on trials 1–5 and for 28 sec on trial 6. (c) B6 mice that had previous experience with distressed demonstrators also expressed increased acquisition of freezing behavior relative to BALB mice when they were exposed to the CS-UCS contingency. Freezing was measured for 28 sec during each CS presentation on trials 7–10. (d) BALB mice that did not have previous experience with distressed demonstrators expressed more freezing behavior than B6 mice to the CS when it was paired with a UCS. Freezing was measured for 28 sec during each CSP presentation on all trials. Asterisks represent a significant difference (P<0.05) between the two genetic backgrounds. All data are presented as the mean ± standard error and were originally reported in Chen et al. (2009).