大鼠抑制性躲避反應的社會學習：一個探索性研究

Abstract

動物為了生存，終其一生都在學習對不同刺激做出適當反應。動物除了依據自身行為的後果進行個別學習(individual learning)外，也可藉觀察(observation)或與其他個體互動(interaction)之社會學習(social learning)過程而改變行為。本研究之目的即在於探討大鼠於實驗室情境中，透過觀察學會躲避嫌惡刺激之社會學習行為。本研究使用抑制性躲避作業發展而成的三種社會學習模型探討大白鼠之社會學習行為。各模型之基本架構如下：學習前經驗期，大鼠接受一可能有助於社會學習之學習前電擊經驗，此經驗已確認不會引起大鼠對後續社會學習時使用之穿梭箱(shuttle box)產生恐懼。學習期間，大鼠兩兩一組在一包含亮暗兩部分之穿梭箱進行社會學習。於暗箱受到電擊之大鼠為示範鼠，僅在一旁觀察之大鼠為觀察鼠。測試期間，所有動物被放入亮箱並自由活動3分鐘，其記憶指標包括首次進入暗箱之潛伏期及3分鐘內逗留於亮箱之時間比例。研究結果發現：觀察同類遭受電擊之經驗不會改變大白鼠之潛伏期，但會增加其逗留於亮箱之偏好。除此之外，此經由觀察獲致之躲避行為只出現於平時缺乏社會互動經驗、與配對示範鼠非同胎手足且互不熟悉之觀察鼠。再者，觀察電擊之經驗不會影響爾後大鼠之痛覺敏感度，且對後續之親身經驗電擊的個別學習沒有任何保留(saving)之效果。綜合以上結果我們認為，雖然動物可透過同類遭受電擊之觀察經驗習得特定形式的躲避反應，但學習結果不若個別學習強勁(robust)。本研究初步證實動物行為會受到觀察同類經驗之影響，但效果相對薄弱。如欲進行效果的操弄，未來需要發展出更可靠之社會學習模型。

Animals can sense and respond to stimuli signaling danger or threat through observing conspecfics having the same experience, and is denoted as social learning whereby an individual may acquires fear and avoidance responses by observing others. However, there have been few studies on the behavioral or neural mechanisms of socially acquired fear to laboratory aversive stimuli. Here we investigated whether a rat can socially acquire a fear and avoidance response in an inhibitory avoidance task. We tested the effect of observing a conspecific being shocked in three different behavioral paradigms that shared basic procedure but varied in the detail. In the probe phase, rats were given a mild shock to induce an experience of being shocked but not a fear response of its own that was known to facilitate subsequent social learning. In the training phase, the “observer” rat observed a “demonstrator” being shocked in the dark compartment of the inhibitory avoidance apparatus. In the retention test, each rat was reintroduced into the lit part and allowed free exploration in the whole apparatus for 3 min. Its first entrance latency into the dark side and the total time spending in the lit part was recorded. The results showed that after observing a conspecific being shocked, the rats failed to show lengthened entrance latencies but spent more time in the lit part. Furthermore, acquisition of avoidance through social learning was only apparent in the isolation-rearing rats which socially trained with an unfamiliar (never seen each other before) and non-littermate companion. Socially-rearing, familiarity or kinship disrupted the social learning effect. Although the effect of social learning was not as robust as individual learning, our results indicated that rats could acquire some kind of preference via social learning. The social learning experience neither affected the observers’ pain sensitivity of shock nor enhanced subsequent individual learning in a saving paradigm. These data, taken together, suggest that an individual might acquire fear through observation. However, the effect was rather weak and the model needs further improvement to afford studies on the neural mechanism.