A Study on Empathy in Rats: Prosocial Behavior in Active Avoidance Task

同理心(empathy)意指源自其他個體的身體狀態產生的情緒反應，同理心可以促進親社會行為(prosocial behavior)，親社會行為意指自發而有利於其他個體的行為。早期行為研究試圖在實驗室複製動物的親社會行為，經常遭遇的批評是無法排除條件化、致敏化與社會促進作用三種非自主性行為的介入，最近的研究使用新的行為典範探討大鼠的親社會行為，但對它們是否真的涉入同理心並沒有直接的證據。本論文使用主動壓桿作業訓練動物學習躲避將出現的電擊或逃脫已出現的電擊，接著讓兩隻老鼠在相鄰的透明實驗箱，只由學習較佳的老鼠按壓槓桿。我們利用共軛情境訓練動物發現按壓槓桿與幫助同伴的必然關聯性，同時引入偶發的遺漏情境來測試動物是否能夠利用這個知識幫助同伴躲避或逃脫電擊，在遺漏情境中操作者按壓槓桿只幫助自己躲避或逃脫電擊，它必須再次按壓槓桿才能幫助同伴。實驗結果發現動物可以再次按壓槓桿幫助同伴逃脫電擊，但無法利用預警訊號協助同伴躲避電擊。在實驗二我們使用分隔測試來檢驗動物的行為是否來自同理心，我們發現動物確實是對於同伴的危難做出反應，而非工具反應、致敏化或社會促進作用。在實驗三我們完全移除操作者的電擊測試動物在自身安全的環境下是否能按壓槓桿幫助同伴，動物同樣可以幫助同伴逃脫電擊，但無法協助躲避。在實驗四我們讓同伴遭受隨機電擊，操作者在安全的環境下仍能按壓槓桿幫助同伴。由以上的結果我們提出動物同理心引發的親社會行為必須具備的三個基本要素：(1)意圖、(2)知識、(3)技能。Empathy is defined as a kind of cognitive and affective reactions appropriate for someone else’s situation rather than one’s own. This empathic concern of others drives human pro-social behavior, which is defined as voluntary behavior intended to benefit the in-group members. Attempting to replicate prosocial behavior in laboratory animals had encountered difficulty and had been criticized for three involuntary confounding factors: Conditioning, sensitization and social facilitation. Recent studies had found several types of pro-social behavior in rats, but whether they indeed involved empathy was still unclear. We trained rats to learn an active avoidance task (AA) depending on a non-reflexive voluntary act—lever pressing. After AA training, two rats were tested in pairs within two transparent adjacent Skinner boxes. Only one lever in one of two boxes was active to prevent or stop delivery of shock and was accessible only to the better trained rat of the pair. To train rat to acquire the contingency between lever pressing and to rescue the neighbored rat from shock, the procedure started with a lever pressing to avoid or escape of shock for both rats in a yoked condition. At the mean time an intermittent leakage condition was introduced to assess if the rat did learn that a lever pressing rescued the partner. The leakage condition was arranged such that pressing the lever saved only the pressed rat rather than both, rescue of the neighbored rat required a second press of the lever after the self-serving first press. Rats did show a higher rate of second press in the leakage condition than in the yoked condition in which the first press saved both and the second press was a random and meaningless act. In next stage, we examined if the second press behavior in the leakage condition continued if the companion partner was removed from the adjacent box. The results showed that this empathic rescuing response dropped to a chance level after the partner’s removal. We further verified that rats would continue this rescuing behavior even the rescuer was no longer endangered but the rescued rat received signaled or not-signaled shocks, even though the rescuer responded more readily to the responses of the shocked companion rather than the signals predicting the upcoming shock. Further analysis ruled out the possibility that this empathy-like sharing of emotion was confounded by conditioning, sensitization or social facilitation. We proposed that the active rescuing behavior observed in our study meets the three key factors characterized pro-social behavior driven by empathy: (1) intention, (2) knowledge and (3) skills