For thousands of years, humans have experimented with different ways to tell time — from sundials and hourglasses to the digital clock.
But even without gadgets, humans have a sense of when things happened and in which order.
Scientists now think they know why. Researchers at the Kavli Institute for Systems Neuroscience in Norway discovered a network of brain cells that timestamps our life experiences as they unfold, allowing us to organize events in our mind.
“The most interesting question in all of science is, ‘How is it that our thoughts are being created by this mass of biological circuitry in the brain?’” said Michael Hasselmo, director of the Center for Systems Neuroscience at Boston University. “This [study] is very essential to understanding our awareness of the world and where that comes from.”
The study in Norway focused on a mysterious part of the brain called the lateral entorhinal cortex. Previous research showed that its neighboring region, the medial entorhinal cortex, plays a key role in how we perceive space and location.
Scientists surgically implanted electrical wires into a group of rats’ lateral entorhinal cortex — wires so thin that they could be wedged in between each brain cell. The rats then ran around freely and scavenged for chocolate cereal, the hat of wires and lights protruding from their skulls. Scientists use the device to record activity in their brains — which neurons were being triggered at any given time.
At first, they expected to see the same pattern of neurons triggered every time the rats repeated a task. But that’s not what they found.
Instead, brain neurons fired off in identifiable patterns that changed with time, marking each event as a new, distinguishable memory. Imagine it as a running sheet of Morse code: Different combinations of neurons indicate when specific actions happened, then that record helps their brains sequence those memories.
“In that sense, it’s a record of time passed,” said Edvard Moser, one of the study’s authors. “We think this is perhaps the way humans and most animals experience time. The brain isn’t good at inferring clock time, but it organizes time in terms of experiences.”
This way of perceiving time is part of a greater phenomenon called episodic memory. It’s the memory of autobiographical events, such as when and where things happened. In the future, the researchers’ discovery could pave the way for treating Alzheimer’s disease — a condition that, by no coincidence, causes many patients to get lost or forget life events.
“The [medial and lateral entorhinal cortex] are among the very first regions damaged in Alzheimer’s disease,” Moser said. “By understanding the mechanisms here better, it will help us find out how Alzheimer’s disease starts and how to detect it earlier.”
Kelly Kasulis is a freelance journalist. Follow her on Twitter: @KasulisK.