The speed at which a minute flies by for us, and how consistently we estimate the duration of events, may be linked to resting metabolic rate, stress hormones and working memory - the ability to hold information in mind briefly. This is the conclusion of a group of scientists led by Darshana Kapri and Professor Martin Picard of Columbia University. The results were published in the journal Psychophysiology.
The study involved 95 adults aged 18 to 60: 59 healthy volunteers and 36 people with rare genetic mitochondrial diseases. These diseases disrupt energy production in cells. Participants performed time-estimation tasks: they had to either say how much time had passed or themselves mark the moment when, by their perception, the given intervals (from 8 to 60 seconds) had elapsed. They also had their resting energy expenditure measured, levels of hormones and mediators in blood and urine measured, working memory tested and brain MRI scans taken.
It turned out that on average people with mitochondrial diseases estimate time the same way as healthy people: neither the speed of the "internal timer" nor the spread in estimates between attempts differed between the groups. However, the biological and cognitive factors linked to the sense of time worked differently in them.
In healthy participants, a higher resting energy expenditure (relative to muscle mass) was associated with lower variability in time estimates, while an elevated level of noradrenaline in urine was associated with greater variability. In other words, the more actively the body burns energy at rest, the more stably a person estimates time. A high noradrenaline level, by contrast, made estimates less stable. These associations persisted after correction for multiple comparisons - a statistical procedure that reduces the risk of chance findings. In people with mitochondrial diseases, such associations were absent or had the opposite direction, although these differences between the groups were not statistically significant.
The most notable discrepancy concerned working memory. In healthy people, better results on the working memory test were associated with a faster "internal timer". In patients with mitochondrial diseases the association was reversed: the better the memory worked, the slower time seemed to pass for them. This inversion persisted after statistical correction. "This is the strongest result of the study," the authors noted. "It suggests that the brains of such patients may achieve a normal sense of time by a different route."
The researchers emphasize that the work is exploratory in nature, and the associations they found are correlational, that is, statistical, and do not by themselves prove a cause-and-effect relationship. In addition, the data were collected at a single point in time, and many analyses were preliminary. The scientists also note that participants could have been mentally counting seconds, which could have influenced the results, especially those related to working memory. Finally, markers of cellular energy were measured from blood cells, which renew quickly and may not reflect the state of long-lived neurons.
"Our sense of time is not only in the head. It is linked to both the brain and the body," the authors conclude. In their view, the data obtained are only the first clues that will point the direction for future research.