Animal and Poultry Science Department, University of Guelph, Guelph, Ontario, Canada.
PLoS One. 2012;7(11):e49180. doi: 10.1371/journal.pone.0049180. Epub 2012 Nov 14.
Animals housed in impoverished cages are often labelled 'bored'. They have also been called 'apathetic' or 'depressed', particularly when profoundly inactive. However, these terms are rarely operationally defined and validated. As a negative state caused by under-stimulation, boredom should increase interest in stimuli of all kinds. Apathy (lack of interest), by contrast, should manifest as decreased interest in all stimuli, while anhedonia (loss of pleasure, a depressive symptom) should specifically decrease interest in normally rewarding stimuli. We tested the hypotheses that mink, a model carnivore, experience more boredom, depression-like apathy, or anhedonia in non-enriched (NE) cages than in complex, enriched (E) cages. We exposed 29 subjects (13 E, 16 NE) to ten stimuli categorized a priori as aversive (e.g. air puffs), rewarding (e.g. evoking chasing) or ambiguous/neutral (e.g. candles). Interest in stimuli was assessed via latencies to contact, contact durations, and durations oriented to stimuli. NE mink contacted all stimuli faster (P = 0.003) than E mink, and spent longer oriented to/in contact with them, albeit only significantly so for ambiguous ones (treatment*type P<0.013). With stimulus category removed from statistical models, interest in all stimuli was consistently higher among NE mink (P<0.0001 for all measures). NE mink also consumed more food rewards (P = 0.037). Finally, we investigated whether lying down while awake and stereotypic behaviour (both increased by NE housing) predicted these responses. Lying awake positively co-varied with certain measures of increased exploration. In contrast, stereotypic 'scrabbling' or locomotion (e.g. pacing) did not. Overall, NE mink showed no evidence of apathy or depression, but instead a heightened investigation of diverse stimuli consistent with boredom. This state was potentially indicated by spending much time lying still but awake (although this result requires replication). Boredom can thus be operationalized and assessed empirically in non-human animals. It can also be reduced by environmental enrichment.
被关在简陋笼子里的动物通常被贴上“无聊”的标签。它们也被称为“冷漠”或“沮丧”，尤其是当它们极度不活跃时。然而，这些术语很少被操作定义和验证。作为一种由刺激不足引起的消极状态，无聊应该会增加对各种刺激的兴趣。相比之下，冷漠（缺乏兴趣）应该表现为对所有刺激的兴趣降低，而快感缺失（失去乐趣，一种抑郁症状）应该特别降低对正常奖励刺激的兴趣。我们测试了以下假设：水貂作为一种典型的肉食动物，在非丰富环境（NE）笼子中比在复杂丰富环境（E）笼子中体验更多的无聊、类似抑郁的冷漠或快感缺失。我们将 29 只水貂（13 只 E，16 只 NE）暴露在十种预先分类为厌恶（如空气冲击）、奖励（如引发追逐）或模棱两可/中性（如蜡烛）的刺激下。通过接触潜伏期、接触持续时间和定向刺激的持续时间来评估对刺激的兴趣。与 E 水貂相比，NE 水貂接触所有刺激的速度都更快（P=0.003），并在接触和定向接触它们时花费的时间更长，尽管只有对模棱两可的刺激才具有显著差异（处理*类型 P<0.013）。在将刺激类别从统计模型中去除后，NE 水貂对所有刺激的兴趣始终更高（所有测量值的 P<0.0001）。NE 水貂还消耗了更多的食物奖励（P=0.037）。最后，我们研究了在清醒状态下躺着和刻板行为（这两者都因 NE 笼养而增加）是否可以预测这些反应。清醒状态下躺着与某些增加探索的措施呈正相关。相比之下，刻板的“抓挠”或运动（如踱步）则没有。总体而言，NE 水貂没有表现出冷漠或抑郁的迹象，而是对各种刺激表现出更高的探索兴趣，这与无聊一致。这种状态可能表现为花费大量时间躺着但保持清醒（尽管这一结果需要重复）。因此，可以在非人类动物中操作化和评估无聊，并通过环境丰富化来减少无聊。
