Rats seem to sigh with relief when an expected electrical shock fails to come, a study has found. Scientists trained rats to expect a shock after a signal, by repeatedly administering a shock after the signal. But during part of the training, the researchers also sometimes gave a second signal, which meant that the expected shock wouldnât come. Thus the rats were trained to associate this signal with a reprieve. After that second signal, the researchers found, the rats often took a deep breathâan act that in humans is correlated with relief.The researchers, with the Nencki Institute of Experimental Biology in Warsaw, wrote a paper on their findings published in the July 20 advance online issue of the research journal Physiology & Behavior. They described the shocks they gave as mild.
A deep breath, or a sigh, is a common action in many mammals that provides extra air to under-ventilated parts of the lungs, wrote the researchers, Stefan Soltysik and Piotr Jelen. âSighs are also correlated with emotions,â they added, including anxiety, anger and resentment âand obviously, judging from the expressionâsigh of reliefâin many languages, with relaxation or relief.â
If sighs can be shown to occur particularly often in conjunction with a specific mood, this might mean theyâre a sign of that mood, they added. The researchers found that rats sighed more than seven times as often during the situation of relief, after the second signal, than during a situation of fear. They also sighed 20 times as often during relief as between trials, they added. âThis clear correlation of sighs with relief (from fear of the tail shock) supports our hypothesis that sighs in social mammals may function as signals of safety,â they wrote.
