How Scratching Monkeys Can Help Us Understand Emotions and Consciousness

Article

Scientists Study Monkeys’ Self-Scratching Behavior to Understand Link between Anxiety and Pessimism

Scientists Sakumi Iki and Ikuma Adachi recently spent a lot of time watching monkeys scratch themselves. Self-scratching among non-human primates is known to indicate social tension and anxiety. The two researchers from Kyoto University, Japan, wanted to use this link to work out whether being anxious (and so scratching a lot) made their monkey subjects more pessimistic, or whether their pessimism was what drove their anxiety (and their scratching).

Findings

Their findings suggest the former is true, as the primates were more likely to make a pessimistic choice if they had scratched their body. This not only provides evidence for an important theory about how physiological changes are linked to emotional states, but also shows that monkeys’ body language can reveal some interesting cues about how animal consciousness may differ from that of humans.

Background

Several studies have previously shown that self-scratching in primates is linked to social tension and emotional state. For instance, a 1991 study found monkeys who were given an anxiety relief drug seemed to scratch themselves less, whereas monkeys who received an anxiety-inducing drug increased self-scratching.

Research

Research has also shown subordinate capuchin monkeys self-scratch more when they are approached by a dominant individual, perhaps due to the increased risk of aggression. Japanese macaques with a high tendency to scratch themselves are less likely to make peace after a conflict with their group companions.

Displacement Behavior

Self-scratching is an example of what behavioral scientists call displacement behavior, which includes yawning, lip-biting, fumbling, and face-touching. Research has shown it can also allow us to better cope with anxiety. For example, in 2012, UK researchers asked participants to do difficult (and in some cases unsolvable) arithmetic calculations in front of an audience, and found that participants who displayed higher rates of self-scratching during the test also reported a lower level of anxiety after the test.

The Study

The researchers at Kyoto University found that macaques seem to have a different relationship to displacement behavior than humans. Iki and Adachi worked with six adult Japanese macaques. They used videos of a macaque scratching themselves to induce self-scratching in their study subjects, since this behavior is contagious, similar to yawning.

The researchers trained the monkeys to choose between different options on a greyscale touchscreen. The darker the shade of grey, the more likely the monkeys were to get a food reward. When they chose the lightest shade of grey, the touchscreen temporarily blanked out. The darkest shade of grey always rewarded the monkeys with food, and the three shades in the middle had inconsistent outcomes.

Results

These stimuli tested whether the monkeys were biased towards optimism or pessimism. The monkeys who self-scratched were more likely to be pessimistic about the outcome of the inconsistent stimuli. The researchers measured pessimism in terms of reaction time. The longer it took a monkey to choose the ambiguous shades, the more pessimistic the researchers believed the monkeys to be. Monkeys didn’t seem to hesitate if they didn’t scratch. The researchers argue that scratching was a sign the monkeys were anxious and being anxious made the monkeys more pessimistic about the future.

Implications

The study supports the James-Lange theory, which argues there is a sequential connection between behavioral and physiological components of emotions and our experience of these emotions. According to this idea, behavioral and physiological responses happen first, which means, for example, that having an irregular heartbeat would make us anxious.

Conclusion

The study highlights interesting similarities, but also differences between humans and other species. A possible difference is related to consciousness. Humans have a conscious experience of their bodily responses, which affects how we respond to them. This is "possibly" a difference, as some researchers argue that other animals, like chimpanzees or elephants, may have some form of consciousness.

Frequently Asked Questions

• What is self-scratching in primates?
  • Self-scratching is a behavior observed in non-human primates, which is linked to social tension and anxiety.
• What is the James-Lange theory?
  • The James-Lange theory is a psychological theory that argues there is a sequential connection between behavioral and physiological components of emotions and our experience of these emotions.
• How does this study contribute to our understanding of animal consciousness?
  • The study shows that monkeys’ body language can reveal interesting cues about how animal consciousness may differ from that of humans. However, it also highlights the importance of studying a wide range of species to better understand what factors shape behavioral and cognitive skills in the animal kingdom.