200917 body clock

Time does fly when we’re having fun

If time seems to go more slowly when you’re boiling the kettle or waiting for a bus, it might not just be your imagination.

Scientists have discovered that time-sensitive neurons in the brain could wear out and distort our perceptions of time, publishing their findings in the Journal of Neuroscience.

These neurons, located in the brain’s supramarginal gyrus (SMG), fire in response to a specific length of time. If the neurons are continually exposed to a stimulus of fixed duration, it seems they get tired.

And because other neurons continue to fire normally, the authors suggest this skews our subjective perception of time.

This is not just an irritation if we’re waiting for something – estimating time down to the millisecond is needed for critical decisions such as those involved in motor control, speech and intricate motor sensory activities like dancing or playing music.

Lead author Masamichi Hayashi, from the University of California, US, says he has long been curious about the neural mechanism of time perception in the brain.

“Why does time pass so quickly when you are having fun? Why does time slow down when you get into a car accident?”

Back in 2015, he says, his team found neural imaging evidence of neurons sensitive to time duration in the SMG – some may respond specifically to a stimulus that lasts 300 milliseconds while others respond to a stimulus that lasts 600 milliseconds.

But it wasn’t clear whether that reflected people’s subjective experience of time or the physical stimulus itself. To test this, Hayashi and co-author Richard Ivry used an illusion of time called duration aftereffect to separate actual versus perceived time spans.

“Duration aftereffect is a phenomenon that repetitive exposure to a flash of light that stays on the screen for a few hundreds of milliseconds alters the perceived duration of the following visual stimulus,” Hayashi explains.

So, after being exposed to a visual stimulus of short duration, say 250 milliseconds, longer visual stimuli lasting between 350 to 650 milliseconds are perceived as longer than they really are.

In contrast, after exposure to longer lasting stimuli, visual stimuli are perceived as shorter than they are.

“This way, by changing the duration of stimuli for exposure, we can manipulate the subjective experience of time without changing the duration of test stimuli,” says Hayashi.

While volunteers experienced this illusion, the researchers scanned and measured their brain activity using functional magnetic resonance imaging (fMRI), discovering that those who showed a greater reduction of brain activity in the SMG also showed greater time distortion.

This suggests “the time sensitive cells in SMG reflect the subjective experience of time,” says Hayashi, adding that these neurons have been found in animals but not before in humans.

He notes that the correlation doesn’t prove that neuron fatigue caused distorted time perception, saying this is an avenue for future research.

Other interesting questions arise too, he adds. For example, how the human brain learns about timing, how people predict time, and whether subjective sense of time can be controlled using brain stimulation techniques.

Mind you, as Adam Sandler’s character in the movie Click discovered, skipping through boring periods of time might not be such a good idea.

Credit: Hayashi and Ivry, JNeurosci 2020.

The Royal Institution of Australia has an Education resource based on this article. You can access it here.

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