The Clock in Your Mind:
Time Perception and the Body

Time - an Elusive Concept

At first glance, time seems straightforward. Physical clocks surround us, providing precise measurements of its passage. Yet our perception of time is far from isn’t shaped solely by objective measures.  A year can feel like it has flown by in the blink of an eye, while waiting three minutes for the microwave to beep can feel like an eternity. Since Einstein’s theory of relativity, the concept of time has been intertwined with the concept of space, with both moving together and influencing one another. Yet this connection isn’t confined to physics. Our brains also link time and space. Specialized brain cells that track elapsed time reside in the hippocampus, a brain region responsible, among other functions, for spatial perception.

Our body operates in cycles that roughly align with the length of a day.  Hormones such as melatonin and cortisol are released in a rhythmic pattern, signaling the body when to sleep and wake, respectively. But how does the body determine this timing? The answer lies in a sophisticated mechanism known as the circadian clock. This internal clock evolved in living organisms long before the invention of man-made timekeeping devices and remains synchronized with the day-night cycle.  Light-sensitive receptors in our eyes detect light and transmit this information to the hypothalamus—a brain region functioning as a "control center," regulating numerous bodily processes. In response, the hypothalamus triggers secretion of the appropriate hormones.

However, the circadian clock isn’t precise enough for the fine distinctions required in our daily dealings with time. The ability to perceive subtle time intervals—such as recognizing when a minute and a half has passed without checking a clock—relies on specialized cells in the hippocampus that estimate elapsed time.

Time-estimating cells are highly susceptible to external influences, including manipulations, as well as our subjective and emotional experiences. Many people, for instance, are familiar with the sensation that time seems to pass more quickly when they are deeply engaged in an activity, particularly an enjoyable one. However, other factors also shape our perception of time—age, for example, plays a significant role in how we experience its passage.

A questionnaire-based study that surveyed participants of different age groups with respect to their experience of the passage of time found that older individuals tend to feel that time passes more quickly. However, another study has found that short-term subjective time estimation—on the scale of seconds—actually improves with age. This suggests that the perception of time speeding up in older adults may be a retrospective impression rather than a real-time shift in perception.

Either way, it is clear that our experience of time is shaped by external factors. Surprisingly, research has shown that time perception is not just a psychological phenomenon—changes in how we perceive time can also influence physiological markers, including skin healing and blood sugar levels.

Certain brain cells in the hippocampus specialize in tracking elapsed time. The hippocampus also plays a key role in spatial perception.
Image credit: Hippocampus region in the human brain | Gray's Anatomy, Wikipedia

The Time Placebo

A growing body of research highlights the intricate connection between the mind and body. One striking example is the placebo effect—where simply believing in the effectiveness of a dummy treatment can lead to real physiological improvements, even when the substance itself has no therapeutic properties. A similar phenomenon occurs when experimental manipulations alter our perception of time.

A study published in PNAS, for instance, found that deliberately altering time perception influenced blood sugar levels in individuals with type 2 diabetes. Researchers divided participants into groups, measured their blood sugar and blood pressure levels, and then asked them to wait for approximately 90 minutes. During the waiting period, participants played computer games while facing a wall clock that displayed time at different speeds depending on their group: one group saw a clock running twice as fast as real time, another group saw a clock running at half speed, and the control group had a clock displaying time at its normal pace. Blood sugar levels were measured again afterward.

The results revealed that participants who believed more time had passed exhibited lower blood sugar levels, as if the rate of sugar clearance from their blood had increased.

Participants who perceived more time had passed exhibited lower blood sugar levels. Image credit: Woman checking blood sugar levels | Dulin, Shutterstock.

 Did You Sleep Well, or Just Think You Did? 

Another study examined how the perception of sleep duration—how long we believe we’ve slept—affects attention and brain activity. Participants spent two consecutive nights in a sleep lab, where the clocks in their rooms were deliberately set to run either faster or slower than real time.

On the first night, all participants slept for eight hours. However, one group was correctly informed that they had slept for eight hours, while the other group was told they had only slept for five hours. On the second night, all participants actually slept for five hours, but again, the information they received varied: one group was told they had slept for eight hours, while the other was informed of the true five-hour duration.

Each morning, participants completed cognitive tests to assess attention. Their brain activity was also recorded using EEG, which measures electrical activity in the brain through external electrodes and maps "brain waves."

The results revealed that participants who believed they had slept for eight hours responded more quickly in cognitive tests, even when they had only slept five hours. Conversely, response times were slower for those who thought they had slept only five hours, despite actually getting a full eight hours of rest. Additionally, a brain activity measure associated with wakefulness was higher in those who believed they had slept for eight hours, regardless of their actual sleep duration. A brain activity indicator linked to fatigue was higher after five hours of sleep compared to eight hours for all participants, but the increase was less pronounced when they believed they had slept for eight hours.

Participants recorded the appearance of their skin after self-administered cupping therapy, which resulted in bruise-like marks Image credit: Person undergoing cupping therapy | Alex Vog, Shutterstock

Shedding Light on the Skin

A study published in late 2023 provides evidence that time perception can influence the rate of skin recovery from mild bruising. Researchers from Harvard University asked participants to self-administer cupping therapy at home—a complementary medicine technique that creates a vacuum on the skin, leading to localized blood vessel dilation and leaving temporary bruise-like marks on the treated area for a few days. Over the course of a week, participants followed daily instructions to perform the treatment and document their bruises, photographing them immediately afterward and again about 30 minutes later. They then uploaded the images to a dedicated app, allowing researchers to measure bruise recovery after half an hour while also establishing participant expectations regarding the expected healing time.

Between the treatment and the second photograph, participants waited 28 minutes under three different conditions: in one, the clock ran at a normal pace; in another, it moved twice as fast; and in the third, it ran at half speed. As a result, the same 28-minute period was perceived as either 56 minutes or 14 minutes .After the waiting period, participants photographed their bruises again, and independent judges—unaware of the experimental conditions—evaluated the images. To ensure consistent results, each participant experienced all three in a varied order.

The findings were striking: in sessions where the clock suggested that 56 minutes had passed, judges rated the bruises as healing slightly faster than in other sessions, even though the actual elapsed time remained the same—28 minutes. In other words, participants’ perception of time appeared to influence the observed rate of bruise recovery.

These findings raise intriguing questions. If the body can heal itself faster, why doesn’t it do so regardless of time perception? What evolutionary advantage could there be in aligning recovery processes or metabolism with our internal sense of time? Does the circadian clock impose limits on possible time manipulations, or could slowing down the clock theoretically extend our lifespan? While these questions remain open, the study underscores a compelling truth: our perception of time doesn’t just shape our experience—it can directly influence physiological healing, highlighting the intricate link between mind and body.