Rhesus monkeys ‘can perceive their own heartbeats’

Rhesus macaques are able to perceive their own heartbeats, according to a new study, in a discovery that could lead to breakthroughs in treating dementia. 

The research creates a first-of-its-kind animal model of interoception, which refers to the ability to sense the internal state of one’s body, such as observing when your heart races or breathing quickens. 

Experts say their findings could support future psychiatric and neuropsychiatric research because impairments in interoception are associated with anxiety, depression, and Alzheimer’s disease. 

The study was carried out by the California National Primate Research Center at the University of California, Davis, and Royal Holloway, University of London.

Researchers monitored four rhesus monkeys sitting in front of an infrared eye tracker that displayed stimuli which bounced and generated a sound either synchronously or asynchronously (faster and slower) with the monkeys’ heartbeats. 

Such an experiment capitalises on the fact that monkeys and human babies look for longer at things that they find surprising or are unexpected, the experts said.

All four monkeys spent more time looking at the stimuli presented out of rhythm with their heartbeats compared to stimuli in rhythm with their heartbeats – suggesting that they sensed that the out of rhythm stimuli were surprising based on the expected rhythm of their heartbeats. 

The results are consistent with evidence previously shown in human infants using a similar method. 

It is the first behavioural evidence that rhesus monkeys have a human-like capacity to perceive their heartbeats and have an interoceptive sense.

‘Why do we care? Interoception, or the self-monitoring of your physiological systems, is involved in all aspects of human life,’ Bliss-Moreau said.

The ability to sense our internal state can indicate issues within the body that require our attention. 

Impaired interoceptive awareness is associated with less capacity to regulate emotions and increased susceptibility to mental health issues such as anxiety and depression.

For example, people with anxiety are aware of their interoceptive signals but they don’t necessarily read them accurately. 

They may misinterpret a small change in heart rate as being much bigger than it really is, which can lead them to ‘catastrophise’ their feelings and amplify their sense of panic. 

Researchers monitored four rhesus monkeys sitting in front of an infrared eye tracker that displayed stimuli which bounced and generated a sound either synchronously or asynchronously (faster and slower) with the monkeys’ heartbeats

‘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,’ Tsakiris said. 

‘The work we present here represents a first successful attempt to fill these gaps.’

Deficits in interoception have also been linked to neurodegenerative diseases like Alzheimer’s disease.

‘This model will be used in future translational studies of neurodegenerative diseases, including Alzheimer’s,’ Bliss-Moreau said. 

‘If we can measure interoception, we can track it as a behavioral biomarker of disease progression.’

The study provides insights into how the rhesus macaque model may be used to further our understanding of brain and body function.

‘A next step is to study the mechanism by which interoception may be involved in different psychiatric and neuropsychiatric conditions,’ Tsakiris said. 

The study has been published in the journal Proceedings of the National Academy of Sciences.