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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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