How do we know where we are? How can we find the way from one place to another? And how can we store this information in such a way that we can immediately find the way the next time we trace the same path?
In the 1940’s, Edward Tolman examined rats moving through labyrinths and found that they could learn how to navigate, and proposed that a “cognitive map” formed in the brain allowed them to find their way. But questions still lingered – how would such a map be represented in the brain?
In 1971, John O’Keefe discovered the first component of this positioning system, a type of nerve cell in the hippocampus that was always activated when a rat was at a certain place in a room. Other nerve cells were activated when the rat was at other places. O’Keefe concluded that these “place cells” formed a map of the room.
In 2005, May-Britt and Edvard Moser discovered another type of nerve cell, which they called “grid cells,” that generate a coordinate system and allow for precise positioning and pathfinding. They were mapping the connections to the hippocampus in rats moving in a room when they discovered an astonishing pattern of activity in a nearby part of the brain called the entorhinal cortex. Certain cells were activated when the rat passed multiple locations arranged in a hexagonal grid. Each of these cells was activated in a unique spatial pattern and collectively these “grid cells” constitute a coordinate system that allows for spatial navigation. This circuitry constitutes a comprehensive positioning system, an inner GPS, in the brain.
In 2014, the Nobel Prize in Physiology or Medicine was awarded to John O’Keefe and May-Britt Moser and Edvard I. Moser for their discoveries.
Recent investigations with brain imaging techniques, as well as studies of patients undergoing neurosurgery, have provided evidence that place and grid cells exist also in humans. In patients with Alzheimer’s disease, the hippocampus and entorhinal cortex are frequently affected at an early stage, and these individuals often lose their way and cannot recognize the environment. Knowledge about the brain’s positioning system may, therefore, help us understand the mechanism underpinning the devastating spatial memory loss that affects people with this disease. The discovery of the brain’s positioning system represents a paradigm shift in our understanding of how groups of specialized cells work together to execute higher cognitive functions. It has opened new avenues for understanding other cognitive processes, such as memory, thinking and planning.
The discoveries of John O’Keefe, May-Britt Moser and Edvard Moser have solved a problem that has occupied philosophers and scientists for centuries – how does the brain create a map of the space surrounding us and how can we navigate our way through a complex environment?
From: https://www.nobelprize.org/prizes/medicine/2014/press-release/
