Why does time fly on some days, but drags on others?

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  • Scientists have been trying to understand how the human brain perceives time
  • In a new study, a pair of researchers finally found some answers
  • With further research, our subjective sense of time could even be manipulated

We’ve all experienced it, depending on the activity, time flies by, while in other situations, such as waiting in a long queue, it just seems to drag on.

A new study, published in the Journal of Neuroscience, answers this puzzling question: time-sensitive neurons get worn out, skewing our perception of time.

This discovery was made after researchers studied people's brain activity during tasks where time was manipulated. According to the findings, neurons in the supramarginal gyrus (SMG) fire in response to a specific length of time. The SMG forms part of the parietal lobe of the brain, and plays a role in phonological processing and emotional responses.

If repeatedly exposed to a stimulus of a fixed duration, the researchers found that the neurons fatigue. And since other neurons continue firing normally, it is our subjective perception of time that becomes skewed, they wrote.

What led to the discovery

In a previous, separate study by the Kavli Institute for Systems Neuroscience, researchers explained that clocks, created by humans, allow us to "measure" time and so, by social contract, we agree to coordinate our own activities according to clock time.

However, they go on to explain that our brain does not perceive the duration of time in the way a wristwatch, for instance, standardises units of minutes and hours. Instead, time in the context of our experiences and memories belongs to an entirely different kind of temporality.

In the case of the recent study, the researchers, Dr Masamichi Hayashi and Dr Richard Ivry, from the Department of Psychology, University of California, measured brain activity with functional magnetic resonance imaging (fMRI) as participants engaged in a time-comparison task.

Healthy adult participants were asked to view a visual adaptor (a grey circle) for a set length of time, 30 times in a row.

Following this, they were shown a test stimulus and indicated its duration.

If the adaptor duration was long, the participants underestimated time, and if the adaptor duration was short, they overestimated time.

The extent of skewed time perception was shown to correlate with how much the activity in the SMG decreased – greater fatigue led to greater time distortion.

brain,time

Image Credit: Hayashi & Ivry, JNeurosci 2020

The subjective nature of our experiences of passing time can, therefore, be said to be mediated by the responses from a group of neurons in the brain, where different subgroups of neurons are suited to different units of time.

Hayashi told Inverse that their discovery is "only the first step" towards fully understanding the neural mechanisms of subjective time experiences, but that their results show some practical takeaways, including that we shouldn’t trust our sense of time, "... especially after you were exposed to stimuli with a constant interval that can lead to neural fatigue of time-sensitive neurons in your brain," he said.

With additional research, scientists may one day be able to manipulate people's subjective sense of time by stimulating these time-sensitive neurons. 

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