Navigation is the most elemental of our skills — “Where am I?” was the first question a creature had to answer — and it’s the one that gives us our tightest connection to the world. The loss of navigational sense is also often the first sign of a mind in decay. Last week, the Nobel Committee announced that this year’s Nobel Prize in Physiology and Medicine will go to three scientists — John O’Keefe and the couple May-Britt and Edvard Moser — whose work has revealed the intricate biological underpinnings of our talent for getting around. O’Keefe discovered the brain’s place cells, which map out particular places, and the Mosers discovered the brain’s grid cells, which give us a general sense of spatial reckoning.
Here’s how I sum up the work of O’Keefe and the Mosers in the “World and Screen” chapter of The Glass Cage:
In a landmark study conducted at University College London in the early 1970s, John O’Keefe and Jonathan Dostrovsky monitored the brains of lab rats as the rodents moved about an enclosed area. As a rat became familiar with the space, individual neurons in its hippocampus—a part of the brain that plays a central role in memory formation—would begin to fire every time the animal passed a certain spot. These location-keyed neurons, which the scientists dubbed “place cells” and which have since been found in the brains of other mammals, including humans, can be thought of as the signposts the brain uses to mark out a territory. Every time you enter a new place, whether a city square or the kitchen of a neighbor’s house, the area is quickly mapped out with place cells. The cells, as O’Keefe has explained, appear to be activated by a variety of sensory signals, including visual, auditory, and tactile cues, “each of which can be perceived when the animal is in a particular part of the environment.”
More recently, in 2005, a team of Norwegian neuroscientists, led by the couple Edvard and May-Britt Moser, discovered a different set of neurons involved in charting, measuring, and navigating space, which they named “grid cells.” Located in the entorhinal cortex, a region closely related to the hippocampus, the cells create in the brain a precise geographic grid of space, consisting of an array of regularly spaced, equilateral triangles. The Mosers compared the grid to a sheet of graph paper in the mind, on which an animal’s location is traced as it moves about. Whereas place cells map out specific locations, grid cells provide a more abstract map of space that remains the same wherever an animal goes, providing an inner sense of dead reckoning. (Grid cells have been found in the brains of several mammal species; recent experiments with brain-implanted electrodes indicate that humans have them too.) Working in tandem, and drawing on signals from other neurons that monitor bodily direction and motion, place and grid cells act, in the words of the science writer James Gorman, “as a kind of built-in navigation system that is at the very heart of how animals know where they are, where they are going and where they have been.”
If “Where am I?” is the first question a creature had to answer, that suggests something else about us, something very important: memory and navigational sense may, at their source, be one and the same. The first things an animal had to remember were locational: Where’s my home? Where’s that source of food? Where are those predators? So memory may have emerged to aid in navigation. That’s something that both O’Keefe and the Mosers have thought about, and that Edvard Moser has begun to explore scientifically:
In addition to their role in navigation, the specialized cells appear to be involved more generally in the formation of memories, particularly memories of events and experiences. In fact, O’Keefe and the Mosers, as well as other scientists, have begun to theorize that the “mental travel” of memory is governed by the same brain systems that enable us to get around in the world. In a 2013 article in Nature Neuroscience, Edvard Moser and his colleague György Buzsáki provided extensive experimental evidence that “the neuronal mechanisms that evolved to define the spatial relationship among landmarks can also serve to embody associations among objects, events and other types of factual information.” Out of such associations we weave the memories of our lives. It may well be that the brain’s navigational sense — its ancient, intricate way of plotting and recording movement through space — is the evolutionary font of all memory.
That would certainly help explain why early memory loss in dementia often manifests itself in a loss of navigational sense.
It was revealing that, when journalists reported on the Nobel last week, they often summed up the scientists’ breakthroughs as involving the discovery of “the brain’s GPS” or our “inner GPS.” That’s a great example of how we often draw on recent technologies as metaphors for the workings of our bodies and minds. Of course, our brains are not receiving signals from satellites (at least not yet); they’re receiving a rich mix of sensory signals about the physical world. The danger in the metaphor is that, in implying a fundamental similarity between an external navigation system and an internal one, it also suggests that which system we use doesn’t matter. Either will get you where you want to go. Lost in the metaphor is the elemental quality of our navigational skill — its importance in connecting us to the world, in giving us a sense of place, and its possible importance to the healthy working of memory. One thing the work of O’Keefe and the Mosers tells us is that the ability to answer the question “Where am I?” through one’s own resources may not be as dispensable a skill as we assume.