LISBON, Portugal — From Aristotle to Albert Einstein, the mysteries of time have engaged human thought. As Einstein once said, “Put your hand on a hot stove for a minute, and it seems like an hour. Sit with a pretty girl for an hour, and it seems like a minute.” Now, a new study is revealing how our brains perceive time, offering the most persuasive evidence to date on the brain’s inner workings.
Researchers from Champalimaud Research’s Learning Lab manipulated neural patterns in rats to change their judgment of time, indicating how our brain perceives the passing of seconds to minutes. Unlike our biological 24-hour clock that dictates daily activities, understanding this short-term time perception is less explored.
Understanding the brain’s clock
The human brain doesn’t rely on a centralized ticking mechanism like a computer. Instead, it depends on a decentralized, flexible understanding of time, determined by active neural networks. Joe Paton, the study’s senior author, says the process is similar to the ripples caused by a stone dropped in a pond. By observing these ripples, one can deduce the stone’s location and timing.
“Just as the speed at which the ripples move can vary, the pace at which these activity patterns progress in neural populations can also shift,” Paton says in a media release. “Our lab was one of the first to demonstrate a tight correlation between how fast or slow these neural ‘ripples’ evolve and time-dependent decisions.”
In the study, rats were trained to discern between varying time intervals. Their brain activity revealed that the faster the neural “ripples” evolved, the longer the time interval seemed, and vice versa. This discovery led the researchers to wonder whether changing these neural dynamics could directly influence the rat’s time perception.
Old techniques bring out new brain insights
Tiago Monteiro, one of the study’s main authors, says researchers used an older technique for their experiments – temperature manipulation. By altering the temperature of a specific brain region, scientists were able to change the tempo of its activity, akin to altering the tempo of a song without changing its notes. This technique was applied to the rat’s striatum, a crucial part of the brain for the experiment.
“We thought temperature could be ideal as it would potentially allow us to change the speed of neural dynamics without disrupting its pattern,” Monteiro says.
Experiments revealed that cooling the striatum made the rats more likely to perceive a time interval as short, while warming it resulted in the opposite effect. Surprisingly, while the striatum has a role in motor control, changing its activity did not alter the rats’ movements. This observation led the researchers to conclude that while the striatum determines “what” action to take, “how” the action is carried out might be governed by other parts of the brain.
Discovering a link to movement disorders
Paton noted the study revealed a potential connection between their findings and movement disorders like Parkinson’s and cerebellar ataxia. While Parkinson’s affects the striatum and can impact movement initiation, sensory cues can help improve movement, likely engaging other parts of the brain. In contrast, those with cerebellar damage struggle with smooth movements but not necessarily with starting or transitioning between them.
Researchers hope this study could pave the way for better treatments for disorders like Parkinson’s and Huntington’s. The study also provides a clearer understanding of the brain’s role in discrete motor control, which may influence future robotics and learning algorithms.
“Ironically, for a paper about time, this study was years in the making,” Monteiro concludes “But there’s plenty more mystery to unravel. What brain circuits create these timekeeping ripples of activity in the first place? What computations, other than keeping time, might such ripples perform? How do they help us adapt and respond intelligently to our environment? To answer these questions, we’re going to need more of something we’ve been studying… time.”
The study was published in the journal Nature Neuroscience.
