Neuroscientist Albert Tsao and his colleagues at the Norwegian University of Science and Technology’s Kavli Institute for Systems Neuroscience have discovered a network of brain cells that express our sense of time within experiences and memories. The researchers observed a neural clock deep inside the brain that organized the flow of experiences into a sequence of events, and published their findings in a paper titled, “Integrating time from experience in the lateral entorhinal cortex” published in Nature in 2018.
The scientists discovered that the region where the brain is timestamping our experiences is in the lateral entorhinal cortex (LEC). The LEC is next to the brain’s positioning system in the medial entorhinal cortex (MEC), where the brain’s “grid cells” are located. This was not a coincidence.
Nobel Prize-winning scientists May-Britt and Edvard Moser worked on the research with Tsao and others. In 2005, the Mosers discovered grid cells, a type of neuron that produce a coordinate system that enables pathfinding and positioning in the medial entorhinal cortex (MEC). Tsao was inspired by the Mosers’ discovery and set out in 2007 to understand the function of the area right next to the MEC, the LEC. The Mosers were awarded the 2014 Nobel Prize in Physiology or Medicine along with John O’Keefe at University College London for their discoveries of cells that constitute the brain’s positioning system. John O’Keefe discovered “place cells” in the hippocampus in 1971. Place cells are nerve cells that forms a map of the surrounding space. Place cells and grid cells in combination enable the brain to position and navigate our environment.
Initially, it wasn’t clear to the research team what the LEC’s purpose was due to frequent changes of cell signals, and the lack of a pattern of activity. A little over a half a decade later, it became apparent to the researchers that it was likely that the signal was changing with time, hence the seeming lack of pattern. The team hypothesized that the LEC network coded for episodic time.
Episodic time is distinctly different from clock time. Episodic time organizes memories in an orderly sequence of event. It is subjective time, based on our brain’s perception, and is related to episodic memories. Episodic memories is the collection of experiences that happened at a particular location and time.
In 2016, researcher Jørgen Sugar tested this theory using laboratory rodents. Initially, a pattern wasn’t readily evident, due to the fact that hundreds or thousands of cells work in unison to create a time signal. In order to find a pattern in the complexity, the team ran big data through detailed statistical analysis. What the team concluded was that the brain uses changes in the environment to determine how much time has elapsed — the less activity, the more difficult it is for the brain to create a time signal. The researchers discovered that by changing activities in an experience, you can alter the time signal in the LEC, and change how the brain perceives time itself. The researchers believe that their discovery will herald an entirely new genre of neuroscientific research in the future.