Monkeys can sense their own heartbeats just like humans, study finds

Rhesus macaques can perceive their own heartbeats, a new study has found. It suggests the research can lead to new animal models to better understand mental illnesses such as anxiety and depression.

The study, published on Monday in the journal PNAS, leads to the development of a first-of-its-kind animal model of interoception, which is the ability to sense the body’s internal state, such as perceiving one’s own heartbeat, breathing, or blushing cheeks.

“Interoception, or the self-monitoring of your physiological systems, is involved in all aspects of human life,” study co-author Eliza Bliss-Moreau from the University of California Davis said in a statement.

This ability to sense the body’s internal state can indicate issues needing attention, and an impaired interoception is linked to less capacity to regulate emotions and increased susceptibility to mental illnesses like anxiety.

Researchers say the findings can lead to new ways of studying psychiatric and neuropsychiatric dysfunctions such as anxiety, depression, and Alzheimer’s disease.

In the study, scientists monitored four rhesus monkeys that sat in front of an infrared eye tracker displaying stimuli that bounced and generated a sound either synchronously or asynchronously (faster or slower) with the monkeys’ heartbeats.

The experiment worked on the basis that monkeys and human babies look for longer at things that they find surprising or unexpected.

Scientists found that all four monkeys spent more time looking at the stimuli presented out of rhythm with their heartbeats, compared to stimuli in sync with their heartbeats.

This suggests that the monkeys sensed the out-of-rhythm stimuli to be surprising based on the expected rhythm of their heartbeats. The result was consistent with previous evidence shown in human infants.

The extent to which the four monkeys paid more attention to out-of-sync stimuli than the in-sync ones was also very close to the difference in human babies, scientists reported in The Conversation.

“These findings strongly suggest that monkeys have an innate sense of their own heartbeats,” they wrote.

Based on the results of the experiment, researchers said rhesus monkeys have a human-like interoceptive sense – which has been found to be key to human emotional experiences, having a sense of self, and even consciousness.

“Interoception is hugely important for emotion regulation and mental health in adults, and yet we know very little about how it develops in early infancy or comes to be across evolutionary time,” Manos Tsakiris, another co-author of the study, said.

In future experiments, scientists hope to understand if some monkeys are better than others at sensing their own heartbeats, and whether variation among the primates in this ability translates to other psychological features.

Since monkeys also have shorter life spans than humans, researchers hope to further study using this animal model how the interoception develops, what environmental features shape it, and what neural systems underlie it – tracking the animals “from womb to tomb”.

“If we can measure interoception, we can track it as a behavioural biomarker of disease progression,” Dr Bliss-Moreau explained.