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Mind & Brain Scientific American Mind Volume 26, Issue 3 Head Lines

The Brain Cells behind a Sense ofDirectionGoal-direction cells add to Nobel Prizewinning discoveries to reveal our internal navigationsystem

By Simon Makin | Apr 9, 2015

After wandering around an unfamiliar partof town, can you sense which direction totravel to get back to the subway or your car?If so, you can thank your entorhinal cortex,a brain area recently identified as beingresponsible for our sense of direction.Variation in the signals in this area mighteven explain why some people are betternavigators than others.

The new work adds to a growingunderstanding of how our brain knowswhere we are. Groundbreaking discoveriesin this field won last year's Nobel Prize inPhysiology or Medicine for John O'Keefe, aneuroscientist at University CollegeLondon, who discovered place cells in the hippocampus, a brain region mostassociated with memory. These cells activate when we move into a specific location, sothat groups of them form a map of the environment.

O'Keefe shared the prize with his former students Edvard Moser and May-Britt Moser,both now at the Kavli Institute for Systems Neuroscience in Norway, who discoveredgrid cells in the entorhinal cortex, a region adjacent to the hippocampus. Grid cellshave been called the brain's GPS system. They are thought to tell us where we arerelative to where we started.

A third typehead-direction cells, also found in the entorhinal regionfires when we

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face a certain direction (such as toward the mountain). Together these specializedneurons appear to enable navigation, but precisely how is still unclear. For instance, inaddition to knowing which direction we are facing, we need to know which direction totravel. Little was known about how or where such a goal-direction signal might begenerated in the brain until the new study.

A team of researchers, led by Hugo Spiers of University College London, asked 16volunteers to familiarize themselves with a virtual environment consisting of a squarecourtyard with a landscape (such as a forest or a mountain) on each wall and a uniqueobject in each corner. They then scanned the participants' brains while showing themviews from the environment and asking them to indicate in which direction differentobjects lay.

The entorhinal region displayed a distinct pattern of activity when volunteers facedeach directionconsistent with how head-direction cells should behave. Theresearchers discovered, however, that the same pattern appeared whether thevolunteers were facing a specific direction or just thinking about it. The findingsuggests that the same mechanism that signals head direction also simulates goaldirection. How, exactly, the brain switches back and forth is unclear, but theresearchers think the brain probably signals which direction you are facing until youconsciously decide to think about where you want to go, at which point the same cellsthen run the simulation.

Interestingly, the more consistent the participants' goal-direction signals were, thebetter they were able to correctly recall in which direction the target objects lay,potentially offering a brain-based explanation for differences in navigational ability.Such results should be interpreted carefully, however. There are many ways worseperformance can lead to weaker effects, cautions Neil Burgess, who heads a differentgroup studying these systems at University College London. For instance, if aparticipant's attention lapses, she or he will not only perform worse but also produceless relevant brain activity.

The work may have clinical relevance. The ability to navigate is often an early casualtyof dementias such as Alzheimer's disease because the entorhinal region is one of thefirst areas to be affected. Spiers's group is working with doctors to develop tests tohelp identify deficits and potentially measure disease progression.

This article was originally published with the title "The brain's homing signal."

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