Time Consciousness Explained

Until very recently, the question of how the brain works to enable the sense of time passing was an enigma. For many psychological functions researchers agree on basic facts related to how we perceive, think, plan, or orient ourselves in space. But the sense of time remained a mystery. In a previous post, I wrote about the reasons why it is difficult to come to conclusive answers.

2023 is an important year for the neuroscience of time perception. Independently of each other, two research groups, Naghibi et al. and Mondok & Wiener, analyzed all existing neuroimaging experiments, such as those using fMRI, to identify brain structures related to the time sense. Meta-analyses are a powerful tool since all available studies are analyzed, in the case of time perception over 100. Only two brain areas were identified to underlie the judgment of duration: the supplementary motor area (SMA) and the insular cortex. The SMA is a brain structure for controlling motor actions and the insula is the decisive brain region to sense body signals. The SMA thereafter would be involved in controlling the timing of movements, the insula would generate our subjective feeling of duration.

Not so long ago, in 2009, the brain scientist A.D. (Bud) Craig wrote for the first time about this idea: Subjective time emerges through the sense of dynamically changing body processes across time. According to Bud, the brain area regulating body feelings, the insula, also creates the sense of time. For example, when we are waiting for something to happen we intensely feel our bodily and emotional self—and time drags. Due to this theoretical background, I was able to understand my own fMRI results of 2010 where in my study the insular cortex of participants showed increasing brain activity with increasing duration—a sign that the insula represents the passage of time.

Over the last few years, the most comprehensive research agenda pointing to the insula as the decisive brain region for subjective time has been conducted by Alice Teghil from Sapienza University in Rome. Since Alice and her coworkers have accumulated such important knowledge on how the body and brain create our sense of time, I asked her to summarize their findings. Here is what she wrote:

It is common sense that we are not always accurate in estimating the passage of time, as it depends on many factors. We are better at judging duration when there is an external signal that helps us to figure out how much time has passed. The most trivial example of such an external signal is the presence of a clock, but also a traffic light predictably turning green, or a rhythmical sound, are informative about the passing of time. We are also able to perceive the passage of time in situations in which there are no external signals concerning elapsing time, like when we have to sit in the dentist’s waiting room and we strongly feel ourselves.

We know that people differ in their ability to perceive “what’s going on” inside the body. Some people can easily forget lunch if they are deeply focused on an important work project; others cannot concentrate anymore when they start feeling hungry. One way to assess this ability is by asking people how often they feel specific bodily sensations, like hunger, thirst, or pain. In one of our experiments, we assessed individual differences in this capacity (called interoceptive sensibility) and developed a novel task to assess the perception of duration when external cues on time passing are available, and when they are not.

Participants first listened to an interval marked by two tones; after that, they were presented a tone again, the beginning of the second interval, and asked to press a key on a laptop when they thought the interval now matched the duration of the first. During the intervals between the two tones, a series of numbers was presented auditorily. The critical manipulation was as follows: unbeknownst to the volunteers, in one condition the presented numbers were temporally arranged into predictable, regular patterns. In the other condition, instead, the numbers were separated by intervals of variable length, creating an irregular temporal pattern. Whereas in the former condition participants could rely on the regular pattern of presentation of the numbers to improve the temporal reproduction of the time intervals, in the latter condition they had to estimate and reproduce durations without relying on external cues on elapsing time. Individuals more sensitive towards their visceral feelings reproduced intervals more accurately. Importantly, this link between the sensibility for bodily states and the perception of time was found only for time intervals filled with irregularly presented numbers.

In another study, we assessed patterns of brain activity in a group of healthy volunteers during a resting period, using fMRI. Individual differences in patterns of brain activity at rest provide important information on neural correlates of mental processes. Outside the scanner, participants performed the same duration reproduction task with regularly and irregularly spaced numbers. We found that the strength of the functional connectivity of the right posterior insula with other regions varied with timing performance in the irregular condition: individuals more able to reproduce the intervals without externals cue also showed stronger connectivity of the posterior insula. These findings are compelling because they show how the insula plays a key role in time perception, and that is even more apparent in those people who are more sensitive to their body signals and can better estimate elapsed time independently from the external environment.

Finally, our research also shows that the insula is causally involved in perceiving time when there are no reliable duration cues. When the insula is damaged after a stroke, patients become less able to accurately reproduce the duration of time intervals filled with irregularly presented numbers.

The study results of Alice and myself show that the experience of time is deeply intertwined with the perception of our bodily states, and that the insula is the brain region responsible for this interplay. Bud Craig had predicted this in his paper from 2009. Our intrinsic ability to sense the passage of time is a result of sensing our body feelings.

In memory of A.D. (Bud) Craig (1951 - 2023).