Time flies on some days, crawls on others: Study locates 'fatigued' neurons that influence our perception of time

On busy days, we feel like the time is not moving fast enough and on the other hand, the duration of any recreational activity feels short. So what makes us feel that time is flying by or dragging along? Some neurons in our brain can be attributed to cause this effect, according to a new study published in the Journal of Neuroscience. The research indicates that the subjective nature of our experiences of passing time are mediated by the responses from a group of neurons in the brain – where different subgroups of neurons are suited to different durations/units of time. These specialized neurons in the brain’s supramarginal gyrus (SMG) fire up in response to the passage of a specific length of time. If they are repeatedly exposed to a stimulus of a fixed duration, biochemical “fatigue” sets in these neurons. Since other neurons continue to function normally, our subjective perception of time gets shaped by this contrast between fatigued and active neurons in the SMG. [caption id=“attachment_8817791” align=“alignnone” width=“750”] The researchers located the SMG, where neurons exhibited a decrease in activity after a duration of adaptation. Image Credit: Hayashi & Ivry, JNeurosci 2020[/caption] Scientists Masamichi J Hayashi and Richard B Ivry used a functional magnetic resonance imaging (fMRI) study to examine the biological basis for the subjective perception of time in several human participants. These adult participants were told to look at a visual adaptor (a grey circle) for a certain length of time, 30 times in a row. After this, they were shown a test stimulus and told to guess the duration it was shown for. The researchers reported that if the stimulus was shown for longer, the participants underestimated the time it was shown for; conversely, if the adaptor duration was short, they overestimated the time. “These results indicate that duration-tuned neural populations in right SMG reflect the subjective experience of time,” the abstract of the study said. The study zeroed in on the right parietal cortex, where the SMG is located in the brain, as the region used to code for time, and responsible for reflecting our subjective experience of time.