Take a moment to pay attention to your body, and all of the sensations within it. Zero in on your heartbeat and try to notice each beat. How strongly can you feel each thump-thump? Do you think you're catching each beat, or are some escaping your perception?

This ability, to feel your heartbeat, along with any other internal sensations in your body, is called interoception. It's the opposite of exteroception—which are signals we receive and process from the outside world, like sight, sound, or touch.

Interoception helps us to regulate our bodies—interoceptive cues tell us when we’re hungry, thirsty, or when we have to pee, so we can do something about it. Yet it’s more than just the body's superintendent. Our internal sensations also interact with our emotions, thoughts, and feelings in meaningful and surprising ways.

Scientists who study the way we sense our bodies are finding that the heartbeat, particularly, can be a direct line to the brain, and the mental states that reside there. Your heartbeat can influence how you feel and how intensely you feel it. It can distract you from remembering things, or make you latch onto them more strongly. And the way each individual feels their own heart beat—how accurate they are, and how accurate they think they are—could predict if they have anxiety, or other various mental health disorders. Even more intriguing, helping people learn to more precisely feel their hearts could soon be a form of treatment for those same disorders.

Throughout the day, our hearts are beating, and we may not be aware of it most of the time. (Maybe you are currently aware, because you've been asked to pay attention.) Every time your heart beats, it sends a signal to your brain, said Sarah Garfinkel, a neuroscientist at the University of Sussex, a leading expert in the heart and its relationship to emotions.

It can seem as though the opposite is true: that it's our emotional states that are in charge, and directing our heart's behavior. When we're scared, it makes our hearts beat faster. But it's actually a two-way street: Our feelings are influenced by signals that come from our bodies too.

This discussion of the connection between body and emotions goes back to William James, often called the father of American psychology. In the late 19th century, he proposed that emotions were simply the names we gave to sensations in our bodies. When our heart is pounding, for example, that physical sensation gives rise to what we know of as "fear." We don't get scared and cause our hearts to beat. Our hearts beat, and make us scared.

This makes some intuitive sense. It's hard to imagine being furious without the physical accoutrements that come with it: a flushed face, a racing heart, clenched teeth, flared nostrils. Or, to feel grief without tears, breathlessness, a pang in the heart. “A purely disembodied human emotion is a nonentity," as James put it.

Today, researchers know from brain imaging that the area of the brain that processes internal sensations, the anterior insula, is also crucial in processing emotions—supporting James' idea that emotions and body are intertwined. Northeastern University neuroscientist Lisa Feldman Barrett has similarly found in her work that emotions are shaped and defined by bodily sensations, past experiences, and emotional concepts from our parents and cultural upbringing. Our emotions are not so much reactions to the world, but inventions of our brains to explain the cause of our sensations.

Fear can be increased by your heartbeat. In 2014, Garfinkel showed study subjects pictures of faces with fearful, happy, disgusted, or neutral expressions. The people who saw the fearful faces at the same time that they were made aware of their hearts beating said they found them to be more intense.

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Interestingly, we all don't have the same abilities when it comes to feeling ourselves. Scientists who study interoception often use heartbeat detection tasks to investigate this variability. They have found differences in how accurate people are at feeling their heartbeats, how good they think they are, and whether or not their beliefs about their interoceptive abilities match their actual accuracy.

People with greater interoceptive accuracy—who can feel their heartbeats more—have more emotional intensity. This has been shown in a number of studies where people are given emotional material, like films to watch. The ones who are more accurate at feeling their heartbeats found the emotional films to be more intense. “This very much aligns with the notion that if you’re more accurate at sensing your heart then it feeds into the intensity of felt emotion,” Garfinkel said.

The fear boost that Garfinkel observed could be even greater in people with anxiety. And this is where Garfinkel's work is turning to now: Rather than just illustrating the connection between heart and mind, she's finding circumstance where a person's interoceptive abilities are somehow associated with a disorder—and thinking about how to use interoception as a tool to help.

There's still so much we don't know about interoception, Garfinkel said. People who are anxious can be overly focused on their bodily sensations. But, as a person with anxiety, am I paying more attention to my heartbeat, or is it behaving in a different way and driving my anxiety? How do we tease apart what's actually happening versus my interoceptive dial being turned all the way on?

Garfinkel and her colleagues are the first to start separating out all these different factors, rather than measuring heartbeat detection as one thing. She said they're finding that self-report measures don't necessarily map on to reality.

Anxious people are more likely to think they have accurate interoception. Just like people can be accurate at perceiving their heartbeat without knowing that they are, anxious people can think they're good at interoception when they're not. “You could think you’re great,” Garfinkel said. “But when we test you in the lab, your accuracy could be quite poor.”

They’ve found that it's this mismatch between how accurate you think you are at feeling your heartbeat and your true accuracy level that is a strong predictor for anxiety symptoms—so, both having lower interoception as well as overestimating your own abilities.

Garfinkel has also looked at interoception in people with autism disorder, who frequently have anxiety, and found that they have lower interoceptive accuracy, too.

“Generally, I think interoception is a feature of psychiatric disorders that is under-recognized and under-represented in science,” said Sahib Khalsa, a neuroscientist at the Laureate Institute for Brain Research in Oklahoma. But that's beginning to change. Khalsa said in the past ten years, it’s becoming clear that interoceptive deficits are present in a wide range of disorders, like panic disorder, depression, eating disorders, somatic symptom disorders, substance use disorders, and PTSD.

Manos Tsakiris, a cognitive neuroscientist at Royal Holloway, University of London, has found that lower interoception is associated with body image dissatisfaction—even if you control for BMI. People with low heartbeat accuracy also tend to objectify their bodies more. “In other words, they tend to think about the bodies, not in terms of health and wellbeing, but in terms of sexual appeal and attractiveness," he said.

In his lab, they're looking closer at this connection: They’ll be doing a study of girls before and after puberty, measuring body image satisfaction along with interoceptive awareness to see how both change over time. He thinks that girls with decent interoception may adjust better to the changes of puberty, and won’t be body-conscious later on.

While interoceptive ability was previously considered a stable trait—one you were stuck with—Garfinkel thinks it's a skill to be improved upon. If low interoceptive accuracy is associated with anxiety or other disorders, perhaps a person could just get better at it.

She's now training people at detecting their heart, and in a forthcoming study that’s currently under peer review, Garfinkel said she's seeing that when people improve upon their accuracy, it reduces their anxiety symptoms.

Khalsa also treats people with anxiety and panic attacks using interoception—his approach is called interoceptive exposure therapy. It pushes patients to engage with their bodily sensations that usually provoke anxiety, like their hearts beating faster, and learn not to treat the signal as dangerous.

Garfinkel thinks a version of interoception therapy could help people with psychosis as well, a population that often experiences dissociation or fees like they're not connected to their body. “Someone who has schizophrenia might be experiencing visual and auditory hallucinations," Khalsa agreed. "So their perceptual faculties might be more engaged outside the body, and that might end up having a consequence on the ability to sense what's happening from within."

Interoception could also help explain why certain existing practices that involve body and mind are effective. Floatation in sensory deprivation tanks has been shown to be helpful for anxiety, with some data finding that just one hour of floating has short-term positive effects for anxiety and depression. It could be because floating briefly cuts off exteroception, or external cues, and forces a person to focus on interoceptive sensations, like your heartbeat.

Mindfulness and meditation also gets people to pay attention to their bodies, Garfinkel said, and she thinks there is an interoceptive component built into it. But the problem is that meditation doesn’t seek to help you be aware of your body better. People don’t usually start a mindfulness practice with the awareness of how good they are at detecting their bodies, it’s based on your own beliefs about your accuracy levels—which could be wrong. Garfinkel thinks that interoceptive testing and training could help make mindfulness a more evidence-based practice with clear goals.

Khalsa's research on meditators has confirmed that: he hasn’t found that meditators are any more accurate at perceiving their heartbeats. “That was really surprising to me,” he said. “What we have found, though, is that when you ask meditators to reflect on their experience of their heartbeat, they seem to talk about it and rate the quality of the experience differently.”

This is the final, important piece of the interoceptive puzzle: Even if you sense your body with greater accuracy, you still have to manage how you interpret those sensations. Sometimes a person in a flotation tank could feel more anxious when faced with their heartbeat. If feeling your heartbeat more accurately is still paired with panic about what it means, it likely won't help with anything.

“You need to just notice that your heart is beating, changing, and have precision into that signal,” Garfinkel said. “But just notice and not worry. Our hearts are awesome, and they’re always doing these sorts of accelerations or decelerations. That is a healthy thing, to have an adaptive heart that beats fast and slow.”

If you can’t make it to a research lab, and you want to know your own interoceptive accuracy, you can take your own pulse while trying to feel your heart, to get a rough sense of your accuracy levels, Garfinkel said. You could also take advantage of a moment your heart is beating quickly, when you’ve just exercised or are scared. “Then notice and see if you can still feel your heartbeat as it returns back to baseline,” Garfinkel suggested.

Even doing this simple exercise can be a reminder that it’s very different to live in your own body than it is to be in someone else's. Your best friend, your partner, your mom—those closest to you could have different levels of interoception, or ascribe different emotional meaning to interoceptive cues. A person’s emotional style, or how they frequently respond to their emotions, may have to do with how they’re feeling their bodies.

“It’s probably one of the biggest unanswered questions of neuroscience and philosophy,” Tsakiris said. “What does it feel like to be somebody? You can know your best friend or your partner better than anybody else, but still you won't really know how it feels like to be himself or herself. There's nothing wrong with that, this is how things are.”

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