The ability to sense the internal state of the body, known as interoception, may be linked to our mental health, and macaques appear to have similar capabilities to us
Rhesus macaques appear to be as sensitive to their own heartbeats as human babies are, suggesting the monkeys have an awareness of their own bodily systems.
The findings could open doors to a better scientific understanding of certain neurological and mental conditions in humans, says Eliza Bliss-Moreau at the University of California, Davis.
Sensing one’s own heartbeat is one of the components of interoception, the capacity to detect the internal state of the body.
Previous studies have suggested that, at least in humans, individual variations in our sensitivity to internal signals and how they are interpreted in the brain might be linked to our emotions, as well as to certain mental and neurological conditions.
Rhesus macaques (Macaca mulatta) have certain structures in the brain and nervous system that suggest they are capable of interoception, but this hasn’t previously been experimentally tested, says Bliss-Moreau.
She and her team came up with a way to test the hypothesis after hearing about a study that found evidence that human babies are sensitive to interoceptive signals.
They monitored the heartbeat of four captive-born adult rhesus macaques while they watched videos that showed a blob-like image bouncing with a rhythm that was either slower, faster or the same as each monkey’s own heartbeat. The team repeated the tests until each monkey had voluntarily completed 100 trials in exchange for sips of fruit juice.
Eye-tracking technology revealed that the monkeys watched the images for significantly longer when the blob’s beat was out of sync with their heartbeat – suggesting they found it surprising, says Bliss-Moreau. On average, the monkeys watched for long enough to see more than twice as many bounces when the beat was faster than their own heartbeat, and about one-and-a-half times as many when the beat was slower.
Like humans, there were individual differences, she says. “All the animals showed [their own] very consistent patterns and the magnitude of the patterns was totally consistent with what’s been seen with human babies,” she says. “That’s pretty exciting.”
Research has suggested that people’s responses to interoceptive signals may have a role in mental health conditions such as anxiety, depression and panic disorder, as well as neurodegenerative conditions like Alzheimer’s disease. Such responses may also have a role in autism. Bliss-Moreau suggests rhesus macaques might serve as useful models for further research into these conditions or forms of development.
The findings add to a growing level of understanding with regard to the capacity of rhesus macaques for self-awareness, says Joey Charbonneau, another member of the team at the University of California, Davis. “There’s strong evidence already that they have these sorts of feelings of knowing things in the most psychological sense, and now we’re adding sort of a physiological component to that,” he says.
Journal reference: PNAS, DOI: 10.1073/pnas.2119868119
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