The Body Clock You Didn't Know You Had

Of everything I found while researching this book, this is the thing that surprised me most. It's not about your brain. It's about your heart.

In 2023, a team at Cornell University published a study that showed something remarkable. They played tones of identical duration to participants while simultaneously monitoring their heartbeats. When a tone was preceded by a shorter-than-average heartbeat, participants perceived that tone as lasting longer. When preceded by a longer-than-average heartbeat, the tone felt shorter.

Time was stretching and compressing in sync with each heartbeat. Not metaphorically. Measurably. The researchers called them "temporal wrinkles."

This finding sits inside a larger body of research on something called interoception, which is your brain's ability to sense what's happening inside your body. Heart rate. Breathing. Gut feelings. Muscle tension. Temperature. Most of this processing happens below conscious awareness. You don't decide to notice your heartbeat. But your brain is tracking it constantly, and that tracking is woven into your perception of practically everything, including time.

Marc Wittmann, a neuroscientist at the Institute for Frontier Areas of Psychology in Freiburg, Germany, has spent decades studying this connection. His key finding is straightforward and profound: bodily processes serve as an internal clock for our sense of time. Not a clock in the mechanical sense. More like a metronome. The rhythm of your body, heartbeat, breathing, arousal level, sets the tempo at which you experience each moment.

The neural real estate for this is the anterior insular cortex, a region of the brain that sits at the intersection of body awareness and time perception. Damage to the right insula reduces people's ability to perceive duration accurately. People with greater interoceptive awareness, meaning those who can more accurately sense their own heartbeat without touching their chest, also reproduce time intervals more accurately.

Your body and your sense of time share a brain region. They're not separate systems. They're intertwined.

This has immediate, practical implications.

Heart rate variability, or HRV, is a measure of the variation in time between successive heartbeats. A higher HRV generally indicates a well-regulated nervous system: your heart speeds up and slows down fluidly in response to demands. A lower HRV indicates a system under strain, locked into a narrow, rigid rhythm. Athletes tend to have high HRV. Chronically stressed people tend to have low HRV.

Research shows that higher HRV predicts more accurate time perception. People with well-regulated nervous systems experience time with better resolution. They perceive durations more faithfully. Their internal metronome is steady, and the temporal experience built on top of it is stable and detailed.

People with lower HRV, on the other hand, tend to experience time less accurately and, critically, tend to perceive it as passing more quickly. A 2025 study found that individuals with higher sympathetic nervous system activity, the branch responsible for fight-or-flight, experienced time as passing faster. Chronic stress doesn't just make you tired. It literally speeds up your experience of time.

This reframes a lot of what we covered in the last few chapters. If your nervous system is running hot, if your resting heart rate is elevated, if your HRV is low, then the metronome underneath your temporal experience is set to a faster tempo. You're not imagining that time is flying. Your body is producing that experience at the physiological level.

And here's where it gets interesting. Heart rate variability is trainable. One of the most effective methods is resonant frequency breathing, which typically lands around 5.5 breaths per minute. At this pace, your heart rate and breathing fall into a synchronised rhythm. Blood pressure oscillations align with respiratory cycles. HRV increases. The nervous system shifts from sympathetic dominance toward a more balanced state.

This isn't meditation in the traditional sense. You don't need to clear your mind or achieve any particular mental state. It's a physiological intervention. You breathe at a specific pace, and your cardiac regulation improves. You do it consistently, and your baseline HRV shifts upward over weeks.

The temporal implication is direct. If HRV predicts temporal accuracy, and if resonant frequency breathing improves HRV, then a daily breathing practice could literally change your experience of time. Not through relaxation, though that's a side benefit. Through recalibration of the physiological system that generates your sense of duration.

I find this more compelling than most mindfulness advice because it doesn't require belief, discipline, or a particular philosophy. It requires ten minutes of breathing at a measured pace. You can do it on a bus. You can do it in a meeting that's going nowhere. The mechanism is mechanical, the evidence is solid, and the intervention is simple.

There's another piece to this. Core body temperature also affects time perception. Higher body temperature correlates with faster subjective time. Lower temperature with slower subjective time. A 2019 study found that increasing core body temperature sped up temporal processing, produced underestimation of time intervals, and created a subjective experience of time pressure. The researchers could literally warm the brain's timing region, the striatum, and watch neural activity patterns warp in time.

This connects to something every runner knows intuitively. During a hard effort, when your body temperature is elevated, time seems to fly. But after you cool down, the memory of the run feels substantial and detailed. The body was hot (fast prospective time) but the brain encoded richly (long retrospective time). Exercise is temporally efficient in the same way flow states are: compressed in the moment, expanded in memory.

The broader point is this. Most of the advice on slowing down time targets your mind. Think differently. Pay more attention. Be present. But the research on interoception suggests the faster lever might be your body. Your nervous system sets the tempo. If you change the tempo, you change the experience.

I'd spent years trying to think my way to a different relationship with time. It turns out I might have been better off starting with my heartbeat.