NOBEL PRIZE : POSITIONING SYSTEM IN THE BRAIN
The Nobel Assembly at
Karolinska Institutet has today decided to award The 2014 Nobel Prize in
Physiology or Medicine with one half to John O´Keefe and the other half jointly
to May-Britt Moser and Edvard I. Moser for their discoveries of cells that
constitute a positioning system in the brain
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? This year´s Nobel Laureates have discovered a positioning
system, an "inner GPS" in the brain that makes it possible to orient
ourselves in space, demonstrating a cellular basis for higher cognitive
function.
In 1971, John O´Keefe discovered the
first component of this positioning system. He found that a type of nerve cell
in an area of the brain called 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.
More than three decades later, in
2005, May-Britt and Edvard Moser discovered another key component of the
brain's positioning system. They identified another type of nerve cell, which
they called "grid cells," that generate a coordinate system and allow
for precise positioning and pathfinding. Their subsequent research showed how
place and grid cells make it possible to determine position and to navigate.
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?
How do we experience our
environment?
The sense of place and the ability
to navigate are fundamental to our existence. The sense of place gives a
perception of position in the environment. During navigation, it is interlinked
with a sense of distance that is based on motion and knowledge of previous
positions.
Questions about place and navigation
have engaged philosophers and scientists for a long time. More than 200 years
ago, the German philosopher Immanuel Kant argued that some mental abilities
exist as a priori knowledge, independent of experience. He considered the
concept of space as an inbuilt principle of the mind, one through which the
world is and must be perceived. With the advent of behavioural psychology in
the mid-20th century, these questions could be addressed experimentally. When
Edward Tolman examined rats moving through labyrinths, he 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?
John O´Keefe and the place in space
John O´Keefe was fascinated by the
problem of how the brain controls behaviour and decided, in the late 1960s, to
attack this question with neurophysiological methods. When recording signals
from individual nerve cells in a part of the brain called the hippocampus, in
rats moving freely in a room, O'Keefe discovered that certain nerve cells were
activated when the animal assumed a particular place in the environment. He
could demonstrate that these "place cells" were not merely
registering visual input, but were building up an inner map of the environment.
O'Keefe concluded that the hippocampus generates numerous maps, represented by
the collective activity of place cells that are activated in different
environments. Therefore, the memory of an environment can be stored as a
specific combination of place cell activities in the hippocampus.
May-Britt and Edvard Moser find the
coordinates
May-Britt and Edvard Moser 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. Here, 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.
Together with other cells of the entorhinal cortex that recognize the direction
of the head and the border of the room, they form circuits with the place cells
in the hippocampus. This circuitry constitutes a comprehensive positioning
system, an inner GPS, in the brain.
A place for maps in the human brain
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
ensembles 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.
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