Humans Have a ‘Sixth Sense’ You’ve Probably Never Heard Of – And It Appears to Be Key For Mental Health : ScienceAlert

We all know that humans have five senses. But a growing body of research shows we have a sixth one that almost nobody talks about – and it may be just as important for our wellbeing as any of the others.

It’s called interoception: the body’s ability to sense and interpret its own internal signals.

This sense detects things that seem ‘invisible’ but are happening constantly: your heart rate, your breathing, your hunger, the temperature running through your body.

“Although we don’t take much notice of it, it’s an extremely important sense as it ensures that every system in the body is working optimally,” psychologists Jennifer Murphy of Royal Holloway University of London and Freya Prentice of University College London wrote in The Conversation in 2022.

“It does this by alerting us to when our body may be out of balance, such as making us reach for a drink when we feel thirsty or telling us to take our jumper off when we’re feeling too hot.”

So far, so simple.

But researchers are now beginning to realize that interoception goes beyond simply regulating our biological needs, and may play a part in a range of mental health conditions – including anxiety, depression, PTSD, and eating disorders.

It’s still early days, but the general idea is that our awareness of things such as our muscle tension, breathing and heart rate can give us important clues about when a situation is ‘safe’ or ‘unsafe’.

When interrupted, this process could contribute to mental health conditions.

Humans Have a 'Sixth Sense' You've Probably Never Heard Of – And It Appears to Be Key For Mental Health — (Maria Korneeva/Moment/Getty Images)

For example, someone with anxiety might be acutely aware of their heart rate in a situation such as a social interaction, which makes them feel uncomfortable in that situation.

Murphy and Prentice’s 2022 analysis of 93 studies found that interoception differs significantly between men and women – with women showing lower accuracy on heart-based tasks in particular.

This may partly explain why conditions like anxiety and depression are more prevalent in women than men from puberty onward, they wrote for The Conversation, though they stressed that the relationship is complex and not fully understood.

But they’re not the only ones exploring this link.

An experiment published in eBioMedicine this year looked at how hunger impacted mood, and showed that people with strong and accurate interoception experienced fewer mood swings than those with poor interoception.

“This does not mean they never felt hungry – they just seemed better at keeping their mood levels stable,” medical psychologist and corresponding author Nils Kroemer from the University of Tübingen in Germany wrote for The Conversation.

One of the most striking pieces of evidence about interoception comes from research on people with anorexia nervosa by scientists at UCLA.

The idea is that in people with anorexia, they have stopped being able to ‘listen’ to their own internal hunger signals.

By testing this interoception with an ingestible vibrating pill, the researchers were actually able to show that this was indeed the case – even after the patients put weight back on.

“People with anorexia nervosa do not simply ignore signals from the body,” said Sahib Khalsa, the study’s senior author and a neuroscientist at UCLA.

“Rather, their nervous system may process gut sensations differently, making those signals harder to detect, trust and learn from. Over time, that may contribute to the persistence of symptoms even after weight is restored.”

However, not everyone is so convinced – an opinion published in Frontiers in Psychology in 2024 claimed “There is no such thing as interoception“.

The authors, led by cognitive scientist Felix Schoeller from MIT, admitted their headline was designed to grab attention, but in reality they believe that researchers may be oversimplifying many different factors under the broad term of this interoceptive sixth sense.

“While the title of this article is intentionally provocative, it serves to highlight a critical issue in the field: namely that the term ‘interoception’ is often used in ways that belie the complexity and diversity of the phenomena it purports to describe,” the team wrote.

And they may have a point. Barry Smith from the University of London claims humans actually have up to 33 different senses.

What we can say for sure is that humans are much more sensory than we give ourselves credit for. Even if we don’t have a name for those senses as yet, they’re already playing a bigger role in our wellbeing than we realize.

“Better understanding all the factors that affect interoceptive ability may be important for someday developing better treatments for many mental health conditions,” wrote Prentice and Murphy.

This article was fact-checked by Michael Irving and edited by Peter Dockrill. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.