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Laughing Rats Are Optimistic

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  • Rafal Rygula
  • Helena Pluta
  • Piotr Popik

Abstract

Emotions can bias human decisions- for example depressed or anxious people tend to make pessimistic judgements while those in positive affective states are often more optimistic. Several studies have reported that affect contingent judgement biases can also be produced in animals. The animals, however, cannot self-report; therefore, the valence of their emotions, to date, could only be assumed. Here we present the results of an experiment where the affect-contingent judgement bias has been produced by objectively measured positive emotions. We trained rats in operant Skinner boxes to press one lever in response to one tone to receive a food reward and to press another lever in response to a different tone to avoid punishment by electric foot shock. After attaining a stable level of discrimination performance, the animals were subjected to either handling or playful, experimenter-administered manual stimulation – tickling. This procedure has been confirmed to induce a positive affective state in rats, and the 50-kHz ultrasonic vocalisations (rat laughter) emitted by animals in response to tickling have been postulated to index positive emotions akin to human joy. During the tickling and handling sessions, the numbers of emitted high-frequency 50-kHz calls were scored. Immediately after tickling or handling, the animals were tested for their responses to a tone of intermediate frequency, and the pattern of their responses to this ambiguous cue was taken as an indicator of the animals' optimism. Our findings indicate that tickling induced positive emotions which are directly indexed in rats by laughter, can make animals more optimistic. We demonstrate for the first time a link between the directly measured positive affective state and decision making under uncertainty in an animal model. We also introduce innovative tandem-approach for studying emotional-cognitive interplay in animals, which may be of great value for understanding the emotional-cognitive changes associated with mood disorders.

Suggested Citation

  • Rafal Rygula & Helena Pluta & Piotr Popik, 2012. "Laughing Rats Are Optimistic," PLOS ONE, Public Library of Science, vol. 7(12), pages 1-6, December.
  • Handle: RePEc:plo:pone00:0051959
    DOI: 10.1371/journal.pone.0051959
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    References listed on IDEAS

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    1. Joseph J. Paton & Marina A. Belova & Sara E. Morrison & C. Daniel Salzman, 2006. "The primate amygdala represents the positive and negative value of visual stimuli during learning," Nature, Nature, vol. 439(7078), pages 865-870, February.
    2. Emma J. Harding & Elizabeth S. Paul & Michael Mendl, 2004. "Cognitive bias and affective state," Nature, Nature, vol. 427(6972), pages 312-312, January.
    3. Nygren, Thomas E. & Isen, Alice M. & Taylor, Pamela J. & Dulin, Jessica, 1996. "The Influence of Positive Affect on the Decision Rule in Risk Situations: Focus on Outcome (and Especially Avoidance of Loss) Rather Than Probability," Organizational Behavior and Human Decision Processes, Elsevier, vol. 66(1), pages 59-72, April.
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    1. Vanessa Kloke & Rebecca S Schreiber & Carina Bodden & Julian Möllers & Hanna Ruhmann & Sylvia Kaiser & Klaus-Peter Lesch & Norbert Sachser & Lars Lewejohann, 2014. "Hope for the Best or Prepare for the Worst? Towards a Spatial Cognitive Bias Test for Mice," PLOS ONE, Public Library of Science, vol. 9(8), pages 1-12, August.

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