Page 5 - IAV Digital Magazine #416

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Scientists Explore Why Time Flies When You're Having Fun
By Brandie Weikle, CBC News
Time stands still when you're stuck in traffic. It flies when you're binge- watching Stranger Things.
A team of neuroscien- tists in Portugal has dis- covered a group of neu- rons in the brains of mice that may help explain why our percep- tion of time
passing — either slow- ly or quickly — is so subjective.
The results of the inves- tigation, conducted at the Champalimaud Centre for the Unknown in Lisbon, were pub- lished Thursday in the journal Science.
The team says its find- ings are the first to pin- point a neural circuitry that affects the judgment of elapsed time.
In order to do so, how- ever, the group spent several months training the mice to judge how much time passed between two sounds.
"We trained mice to esti- mate whether the dura- tion of an interval between two tones was shorter or longer than 1.5 seconds," said prin- cipal investigator Joe Paton in a statement about the findings. The mice indicated their choice — longer or shorter — by placing their snouts either on a left or right port.
The next step was to examine what was going
on deep in the brain when the animals made their estimates.
Using a tech- nique called fiber photome- try, the researchers began to meas- ure signals that reflected the electrical activity of dopamine neurons in a part of the brain called the sub- stantia nigra pars compacta, known to play a role in process- ing how time passes.
Scientists have understood for some time that, in humans, the substantia nigra is associated with our internal clocks. In fact, destruc- tion of this part of the brain is a cause of Parkinson's disease, one of the symptoms of which is impaired per- ception of time.
Watching this area of the brain in their rodent sub- jects was illuminating for the researchers, who found that when neural activity was high the ani- mals tended to underes- timate the amount of time that had passed. In other words, time seemed to be passing quickly.
The team then per- formed a round of exper- iments to see if they could confirm a causal link between a higher
level of neural activity and this apparent "faster" passing of time. They used light to stimulate neurons in the animals' brains and note how that impacted their performance on the task.
"We found that if we stimulated the neurons, the mice tended to underestimate duration, and if we silenced them, they tended to overesti- mate it," said Paton.
"This result, together with the naturally occur- ring signals we observed in the previous experi- ments, demonstrate that the activity of these neu- rons was sufficient to alter the way the animals judged the passage of time."
A similar phenomenon could be at work when, stuck in that traffic jam with nothing to occupy it apart from your to-do list and worrying about get- ting to your destination on time, your brain over- estimates the amount of time passed.
Paton said the research has never been more personally relevant to him than it was recently when two of his friends were in a serious accident.
"The few hours between when we knew about the accident and when we knew that they would be okay ... felt like weeks. In retrospect, I wonder what role these neurons
we have been studying might have played in that illusion," said Paton in the statement.
Perception of time plays a more critical role than simply determining if a brain is bored or enter- tained.
"Timing is important for extracting information from the environment and deciding when to expect something to happen or when to engage or disengage from an action,"
said Paton.
For example, the longer it lingers, a rabbit feed- ing in an open field increases its chances that a predator will sneak up.
While the authors say it is very likely that a simi- lar circuit is at work in the human brain, the findings are limited by the fact that the animals can't tell
researchers what they felt.
"When we study ani- mals, the only thing we can measure is the ani- mal's behaviour. But we are never sure of what they perceive," said Paton.
"We interpret this as 'a subjective experience of the animal' but it's no more than an interpreta- tion. And that's the best we can do."
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