Hamsters can experience happiness, optimism, sadness and depression much the way that we do, suggests a new study that describes a method for determining the feelings of these cute and cuddly popular pets.
While the tests are best left to scientists, the end results are clear: hamsters love extra comforts, such as comfy hammocks, ample bedding material, ledges, chew toys and snacks. Without these and other perks, the furry rodents show signs of depression, indicates the study, which is published in the new issue of Royal Society Open Science.
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Authors Emily Bethell and Nicola Koyama of Liverpool John Moores University explain that "cognitive measures may detect shifts in emotion not apparent from behavioral observation or traditional behavioral tests of emotion alone."
In other words, a person could spend all day watching a hamster, and not really know what it is feeling. This is not to say that the rodents don't experience many emotions. Instead, we do not easily detect their social cues. It's not as though a hamster can look up, flash a smile and say, "I feel great today!"
To get around this problem, scientists have developed a "go/no-go" task to measure levels of optimism that, in turn, are linked to feeling of happiness or sadness in humans and other animals.
In this case, the researchers trained 30 captive-born male Syrian hamsters to approach a drink station at one location to obtain a reward (i.e., to go toward sugar water) and to refrain from approaching a drink at another location to avoid an aversive liquid ("no go"). The scientists then created ambiguous situations in which it was unclear to the hamster if the drinker offered a reward or the bad-tasting liquid.
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The scientists included a number of controls and additional behavioral tests to overcome possible limitations, such as odors released by the drinks.
Before the tests, some of the hamsters were raised with multiple comforts, such as soft extra bedding, while the others just received basic care. Hamsters given the added "enrichments" repeatedly exhibited more optimism in their decision-making throughout the study.
Bethell and Koyama wrote that "the addition of extra cage enrichment leads to a more ‘optimistic' judgment bias in the hamsters. Removal of the additional enrichment items (back to standard enrichment condition which hamsters were used to) resulted in a negative shift."
Similar studies have involved rats, mice, cats, dogs, dairy calves, sheep, chickens, honeybees, rhesus macaques, marmosets, starlings, pigs, horses and goats.
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The researchers explained, "So far, studies have revealed that manipulations presumed to create a negative state (such as disrupted housing conditions or dehorning in calves) lead to reduced responses (more ‘no-go's) to the ambiguous probes. This negative shift in judgment bias is presumed to arise from a negative shift in underlying emotion state."
They continued, "Positive manipulations (e.g. addition of environmental enrichment) generally lead to increased responses (more ‘go's) at one or more of the ambiguous probes. This is presumed to arise from positive shifts in judgment bias and underlying emotion state."
It is known that happy people make more optimistic decisions, while depressed individuals tend to make more negative assumptions, so studies on humans support the new research's overall findings.
You might say that it's common sense that a pampered person or pet will be happier than those without such comforts, but, as mentioned earlier, proving this for animals whose visual and audible communications we don't understand is difficult.
The researchers hope that their work will "lead to improved welfare assessment across species."