Decentralized Time Perception in Animals: The Population Clock Hypothesis

Friday - July 21 2023, 18:47 UTC - 1 year ago

Researchers at Champalimaud Researchhave discovered a way to manipulate the brain's perception of time by controlling neural activity in rats, and the Population Clock Hypothesis suggests that the brain maintains a decentralized and flexible sense of time which could be influenced by patterns of activity evolving in groups of neurons during behavior. By artificially slowing down or speeding up these neural patterns, scientists were able to ahce and warp their judgement of time duration.

The Learning Lab at Champalimaud Research has discovered a way to manipulate the brain’s perception of time by controlling neural activity in rats. Their research, which has potential applications in treating diseases like Parkinson’s and Huntington’s, could also influence the fields of robotics and learning algorithms.

From Aristotle’s musings on the nature of time to Einstein’s theory of relativity, humanity has long pondered: how do we perceive and understand time? The theory of relativity posits that time can stretch and contract, a phenomenon known as time dilation. Just as the cosmos warps time, our neural circuits can stretch and compress our subjective experience of time. As Einstein famously quipped, "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." .

In new work from Champalimaud Research’s Learning Lab published in the journal Nature Neuroscience, scientists artificially slowed down, or sped up, patterns of neural activity in rats, warping their judgment of time duration and providing the most compelling causal evidence so far for how the brain’s inner clockwork guides behavior.

In contrast to the more familiar circadian clocks that govern our 24-hour biological rhythms and shape our daily lives, from sleep-wake cycles to metabolism, much less is known about how the body measures time on the scale of seconds to minutes. The study focused precisely on this seconds-to-minutes timescale at which much of our behavior unfolds, whether you’re waiting at a stop light or serving a tennis ball.

The Population Clock Hypothesis .

Unlike the exact ticking of a computer’s centralized clock, our brains maintain a decentralized and flexible sense of time, thought to be shaped by the dynamics of neuronal networks dispersed across the brain. In this "population clock" hypothesis, our brains keep time by relying on consistent patterns of activity evolving in groups of neurons during behavior.

Joe Paton, the study’s senior author, likens this to dropping a stone into a pond. "Each time a stone is dropped, it creates ripples that radiate outward on the surface in a repeatable pattern. By examining the patterns and positions of these ripples, one can deduce when and where the stone was dropped into the water." .

"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. 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." .

The researchers trained rats to distinguish between different intervals of time. They found that activity in the striatum, a deep brain region, follows predictable patterns that change at different speeds: when animals report a given time interval as longer, the activity evolves faster, and when they report it as shorter, the activity evolves more slowly.

However, correlation does not imply causation. "We wanted to test whether variability in the speed of striatal population dynamics merely correlates with or directly regulates timing behav¬ior," Paton explains.