医学・生理学賞に欧州の３人「脳の空間認識」解明
ことしのノーベル医学・生理学賞に、脳の中に、自分が今どこにいるのかを把握する神経細胞があることを発見し、脳の空間認識のメカニズムを解明したイギリスとノルウェーで活動している研究者ら３人が選ばれました。

スウェーデンのストックホルムにあるノーベル賞の選考委員会は、日本時間の午後６時半ごろ記者会見し、ことしのノーベル医学・生理学賞に、▽イギリスで活動しているジョン・オキーフ氏、▽ノルウェーで活動しているマイブリット・モゼール氏、そして夫の▽エドバルド・モゼール氏の３人を選んだと発表しました。
オキーフ氏は、動物はなぜ、自分が今いる位置を感覚的に把握できるのか、その理由を突き止めようと、ラットを使った実験を行い、まず、脳の中でも「海馬」と呼ばれる記憶に関わる部位に注目しました。
その結果、海馬の中に、自分が今どこにいるのかを把握する神経細胞があり、この細胞をつないだ神経のネットワークがあることを突き止めました。
さらに、モゼール夫妻は、大脳新皮質にも、自分の今の位置を距離も含めて把握する別の神経細胞があることを突き止め、脳が空間を認識するメカニズムを解明しました。
ノーベル賞の選考委員会は、３人を選んだ理由について、「アルツハイマー病などの患者が、はいかいするのは、これらの細胞などの脳の機能に異常が出るためだと考えられる。記憶や意識など脳の情報処理のメカニズムに迫る研究で、常識を覆す成果だ」とコメントしています。
http://www3.nhk.or.jp/news/html/20141006/k10015173391000.html

The Brain’s Navigational Place and Grid Cell System
Press Release
2014-10-06

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 (Figure 1). 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 (Figure 2). 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 (Figure 3).

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.

Key publications:
O'Keefe, J., and Dostrovsky, J. (1971). The hippocampus as a spatial map. Preliminary evidence from unit activity in the freely‐moving rat. Brain Research 34, 171-175.

O´Keefe, J. (1976). Place units in the hippocampus of the freely moving rat. Experimental Neurology 51, 78-109.

Fyhn, M., Molden, S., Witter, M.P., Moser, E.I., Moser, M.B. (2004) Spatial representation in the entorhinal cortex. Science 305, 1258-1264.

Hafting, T., Fyhn, M., Molden, S., Moser, M.B., and Moser, E.I. (2005). Microstructure of spatial map in the entorhinal cortex. Nature 436, 801-806.

Sargolini, F., Fyhn, M., Hafting, T., McNaughton, B.L., Witter, M.P., Moser, M.B., and Moser, E.I. (2006). Conjunctive representation of position, direction, and velocity in the entorhinal cortex. Science 312, 758-762.

John O’Keefe was born in 1939 in New York City, USA, and holds both American and British citizenships. He received his doctoral degree in physiological psychology from McGill University, Canada in 1967. After that, he moved to England for postdoctoral training at University College London. He has remained at University College and was appointed Professor of Cognitive Neuroscience in 1987. John O´Keefe is currently Director of the Sainsbury Wellcome Centre in Neural Circuits and Behaviour at University College London.

May-Britt Moser was born in Fosnavåg, Norway in 1963 and is a Norwegian citizen. She studied psychology at the University of Oslo together with her future husband and co-Laureate Edvard Moser. She received her Ph.D. in neurophysiology in 1995. She was a postdoctoral fellow at the University of Edinburgh and subsequently a visiting scientist at University College London before moving to the Norwegian University of Science and Technology in Trondheim in 1996. May-Britt Moser was appointed Professor of Neuroscience in 2000 and is currently Director of the Centre for Neural Computation in Trondheim.

Edvard I. Moser was born in born 1962 in Ålesund, Norway and has Norwegian citizenship. He obtained his Ph.D. in neurophysiology from the University of Oslo in 1995. He was a postdoctoral fellow together with his wife and co‐Laureate May‐Britt Moser, first at the University of Edinburgh and later a visiting scientist in John O´Keefe´s laboratory in London. In 1996 they moved to the Norwegian University of Science and Technology in Trondheim, where Edvard Moser became Professor in 1998. He is currently Director of the Kavli Institute for Systems Neuroscience in Trondheim.

Image illustrating the 2014 Medicine PrizeImage (pdf 204 Kb)

The Nobel Assembly, consisting of 50 professors at Karolinska Institutet, awards the Nobel Prize in Physiology or Medicine. Its Nobel Committee evaluates the nominations. Since 1901 the Nobel Prize has been awarded to scientists who have made the most important discoveries for the benefit of mankind.

Nobel Prize® is the registered trademark of the Nobel Foundation

Scientific Background

The Brain’s Navigational Place and Grid Cell System

The 2014 Nobel Prize in Physiology or
Medicine is awarded to Dr. John M. O’Keefe,
Dr. May-Britt Moser and Dr. Edvard I.
Moser for their discoveries of nerve cells in
the brain that enable a sense of place and
navigation. These discoveries are ground
breaking and provide insights into how
mental functions are represented in the
brain and how the brain can compute
complex cognitive functions and behaviour.
An internal map of the environment and a
sense of place are needed for recognizing
and remembering our environment and for
navigation. This navigational ability, which
requires integration of multi-modal sensory
information, movement execution and
memory capacities, is one of the most
complex of brain functions. The work of the
2014 Laureates has radically altered our
understanding of these functions. John
O’Keefe discovered place cells in the
hippocampus that signal position and
provide the brain with spatial memory
capacity. May-Britt Moser and Edvard I.
Moser discovered in the medial entorhinal
cortex, a region of the brain next to
hippocampus, grid cells that provide the
brain with an internal coordinate system
essential for navigation. Together, the
hippocampal place cells and the entorhinal
grid cells form interconnected nerve cell
networks that are critical for the
computation of spatial maps and
navigational tasks. The work by John
O’Keefe, May-Britt Moser and Edvard Moser
has dramatically changed our
understanding of how fundamental
cognitive functions are performed by neural
circuits in the brain and shed new light onto
how spatial memory might be created.

Introduction

The sense of place and the ability to navigate
are some of the most fundamental brain
functions. The sense of place gives a
perception of the position of the body in the
environment and in relation to surrounding
objects. During navigation, it is interlinked
with a sense of distance and direction that is
based on the integration of motion and
knowledge of previous positions. We
depend on these spatial functions for
recognizing and remembering the
environment to find our way.

Questions about these fundamental brain
functions have engaged philosophers and
scientists for a long time. During the 18th
century the German philosopher Immanuel
Kant (1724-1804) argued that some mental
abilities exist independent of experience. He
considered perception of place as one of
these innate abilities through which the
external world had to be organized and
perceived.

A concept of a map-like representation of
place in the brain was advocated for by the
American experimental psychologist Edward
Tolman, who studied how animals learn to
navigate (Tolman, 1948). He proposed that
animals could experience relationships
between places and events and that the
exploration of the environment gradually
resulted in the formation of a cognitive map
that enabled animals to navigate and find
the optimal path through the environment.
In this view, cognitive maps represent the
environment as a gestalt that allows the
subject to experience the room and navigate.


Tolman’s theory opposed the prevailing view
among behaviourists that complex
behaviours are achieved by chains of
sensory-motor response relationships. But it
did not address where in the brain these
functions may be localized and how the
brain computes such complex behaviours.
The advent of techniques to record from
cells in the brain of animals that were freely
moving in the environment, using chronically
implanted micro wires (Sturmwasser, 1958),
made it possible to approach these
questions.

Finding the place cells

John O’Keefe had a background in
physiological psychology, working with
Ronald Melzack at McGill University before
he moved to the laboratory of the pain
researcher Patrick Wall at University College
in London, where he started his work on
behaving animals in the late 1960s. There he
discovered the place cells, when recording
from neurons in the dorsal partition of
hippocampus, called CA1, together with
Dostrovsky, in rats moving freely in a
bounded area (O'Keefe and Dostrovsky,
1971) (Figure 1).

Figure 1. Place cells. To the right is a schematic of the
rat. The hippocampus, where the place cells are
located is highlighted. The grey square depicts the
open field the rat is moving over. Place cells fire when
the animal reaches a particular location in the
environment. The dots indicate the rat’s location in
the arena when the place cell is active. Different place
cells in the hippocampus fire at different places in the
arena. F:\N 2014\final\images for sci back\Fig1.jpg

The firing pattern of these cells was
completely unexpected. Place cells were
active in a way that had not been seen for
any cells in the brain before. Individual place
cells were only active when the animal was
in a particular place in the environment,
namely their place field. By systematically
changing the environment and testing
different theoretical possibilities for the
creation of the place fields O’Keefe showed
that place cell firing did not merely reflect
activity in sensory neurons, but that it
represented a complex gestalt of the
environment.

Different place cells could be active in
different places and the combination of
activity in many place cells created an
internal neural map representing a particular
environment (O'Keefe, 1976; O'Keefe and
Conway, 1978). O’Keefe concluded together
with Nadel that place cells provide the brain
with a spatial reference map system, or a
sense of place (O'Keefe and Nadel, 1978). He
showed that the hippocampus can contain
multiple maps represented by combinations
of activity in different place cells that were
active at different times in different
environments. A specific serial combination
of active place cells may therefore represent
a unique environment, while other
combinations represent other environments.
Through O’Keefe’s discoveries, the cognitive
map theory had found its representation in
the brain.

A prerequisite for O’Keefe’s experiments
was the development of appropriate
recording techniques to be used in freely
moving animals. Although O’Keefe was an
early user of these techniques, he was not
the first to record from hippocampal or
other nerve cells in intact animals (see
O’Keefe and Nadel 1978). However,
researchers mostly used restricted
behavioural task or strict stimulus-response
protocols. In contrast, O’Keefe recorded the


cellular activity during natural behaviour,
which allowed him to observe the unique
place fields and relate the neural activity in
the place cells to represent the sense of
place.

In subsequent experiments, O’Keefe showed
that the place cells might have memory
functions (O'Keefe and Conway, 1978;
O'Keefe and Speakman, 1987). The
simultaneous rearrangement in many place
cells in different environments was called
remapping and O’Keefe showed that
remapping is learned, and once it is
established, it can be stable over time (Lever
et al., 2002). The place cells may therefore
provide a cellular substrate for memory
processes, where a memory of an
environment can be stored as specific
combinations of place cells.

At first, the proposition that the
hippocampus was involved in spatial
navigation was met with some scepticism.
However, it was later appreciated that the
discovery of place cells, the meticulous
demonstration that these cells represent a
mental map far from primary sensory input,
and the proposal that hippocampus contains
an inner map that can store information
about the environment, were seminal.
O’Keefe’s discovery sparked a large number
of experimental and theoretical studies on
how place cells are engaged in generating
spatial information and in spatial memory
processes. The general notion from these
studies is that the key function of the place
cells are to create a map of the environment,
although they may also be involved in
measuring distance under some
circumstances (Ravassard et al., 2013).

From hippocampus to grid cells in the
entorhinal cortex

Through the 1980s and 1990s the prevailing
theory was that the formation of place fields
originated within the hippocampus itself.
May-Britt Moser and Edvard Moser, who
were studying the hippocampus, both during
their PhD work in Per Andersen’s laboratory
in Oslo and afterwards both as visiting
scientists in Richard Morris’ laboratory in
Edinburgh and John O’Keefe’s laboratory in
London, asked whether the place cell firing
can be generated from activity outside
hippocampus. The major input to the
hippocampus comes from a structure on the
dorsal edge of the rat’s brain, the entorhinal
cortex. A large part of the output from the
entorhinal cortex projects to the dentate
gurus in hippocampus, which in turn connect
to the region in the hippocampus called CA3,
and further to CA1 in the dorsal
hippocampus. Interestingly, this is the same
the part of the brain in which John O’Keefe
first found the place cells. In 2002, the
Mosers found that disconnecting projections
from the entorhinal cortex through CA3 did
not abolish the CA1 place fields (Brun et al.,
2002). These findings, and the knowledge
that medial entorhinal cortex is also directly
and reciprocally connected to the CA1
region, prompted May-Britt Moser and
Edvard Moser to look in the medial
entorhinal cortex for place coding cells. In a
first study they established, similar to what
others had shown, that the medial
entorhinal cortex contained cells that shared
characteristics with the place cells in
hippocampus (Fyhn et al., 2004). However,
in a later study using larger encounters for
the animals to move in, they discovered a
novel cell type, the grid cells, that had
unusual properties, (Hafting et al., 2005).

The grid cells showed an astonishing firing
pattern. They were active in multiple places
in the open box that together formed nodes
of an extended hexagonal grid (Figure 2),
similar to the hexagonal arrangements of
holes in a beehive.

Grid cells in the same area of the medial
enthorinal cortex fire with the same spacing


and orientation of the grid, but different
phasing, so that together they cover every
point in the environment.

F:\N 2014\final\images for sci back\Fig2.jpg

Figure 2. Grid cells. The grid cells are located in the
entorhinal cortex depicted in blue. A single grid cell
fires when the animal reaches particular locations in
the arena. These locations are arranged in a
hexagonal pattern.

The Mosers found that the distance of the
grid fields varies in the medial entorhinal
cortex with the largest fields in the ventral
part of the cortex. They also showed that the
grid formation did not arise out of a simple
transformation of sensory or motor signals,
but out of complex network activity.

The grid pattern had not been seen in any
brain cells before! The Mosers concluded
that the grid cells were part of a navigation
or path integration system. The grid system
provided a solution to measuring movement
distances and added a metric to the spatial
maps in hippocampus.

The Mosers further showed that grid cells
were embedded in a network in the medial
entorhinal cortex of head direction cells and
border cells, and in many cases, cells with a
combined function (Solstad et al., 2008).
Head-direction cells were first described by
James Ranck (1985) in another part of the
brain, the subiculum. They act like a
compass and are active when the head of an
animal points in a certain direction. Border
cells are active in reference to walls that the
animal encounters when moving in a closed
environment (Solstad et al., 2008; Savelli, et
al. 2008). The existence of border cells was
predicted by theoretical modelling by
O’Keefe and colleagues (Hartley, et al. 2000).
The Mosers showed that the grid cells, the
head direction cells, and the border cells,
projected to hippocampal place cells (Zhang
et al. 2013). Using recordings from multiple
grid cells in different parts of the entorhinal
cortex, the Mosers also showed that the grid
cells are organized in functional modules
with different grid spacing ranging in
distance from a few centimetres to meters,
thereby covering small to large
environments.

The Mosers further explored the
relationship between grid cells and place
cells in theoretical models (Solstad et al.,
2006), lesion experiments (Bonnevie et al.,
2013; Hafting et al., 2008), and in remapping
experiments (Fyhn et al. 2007). These and
other studies by Mosers and O’Keefe, as well
as by others, have shown that there is a
reciprocal influence between grid cells in the
medial entorhinal cortex and place cells in
the hippocampus and that other spatially-
tuned cells in the entorhinal cortex, in
particular the border cells (Figure 3), may
contribute in the generation of the firing
pattern of the place cells (Brandon et al.,
2011; Koenig et al., 2011; Bush, Berry and
Burgess, 2014, Bjerkness et al. 2014).

F:\N 2014\final\images for sci back\Fig3.jpg

Figure 3. A schematic showing grid cells (blue) and
place cells (yellow) in the entorhinal cortex and
hippocampus, respectively.


The Mosers’ discovery of the grid cells, a
spatial metric coordination system, and their
identification of the medial entorhinal cortex
as a computational centre for spatial
representation, is a break-through that
opens up new avenues to advance the
understanding of the neural mechanisms
underlying spatial cognitive functions.

The grid and place cell systems are
found in many mammalian species
including humans

Since the initial description of place and grid
cells in rat and mice, these cell types have
also been found in other mammals (Killian et
al., 2012; Ulanovsky et al., 2007; Yartsev et
al., 2011, 2013;). Humans have large
hippocampal-entorhinal brain structures and
these structures have long been implicated
in spatial learning and episodic memory
(Squire, 2004). A number of studies support
the idea that the human brain has a spatial-
coding system that is similar to that found in
non-human mammals. Thus, researchers
have found place-like cells in the
hippocampus (Ekstrom et al., 2003; Jacobs
et al., 2010) and grid-like cells in the
entorhinal cortex (Jacobs et al., 2013) when
directly recording from nerve cells in the
human brain of patients with epilepsy
undergoing pre-surgical investigation. Using
functional imaging (fMRI). Doeller et al.
(2010) have also provided support for the
existence of grid cells in the human
entorhinal cortex.

The similarity of the hippocampal-entorhinal
structure in all mammals and the presence
of hippocampal-like structures in non-
mammalian vertebrates with navigational
capacity suggest that the grid-place cells
system is a functional and robust system
that may be conserved in vertebrate
evolution.

The importance of the discovery of
place cells and grid cells for research
in cognitive neuroscience

It is an emergent theme that place-coding
cells in the hippocampal structures are
involved in storing and/or retrieving spatial
memories. In the 1950s Scoville and Milner
(1957) published their report on the patient
Henry Molaison (HM), who had his two
hippocampi surgically removed for
treatment of epilepsy. The loss of
hippocampi caused severe memory deficits,
as evident by the clinical observation that
HM was unable to encode new memories,
while he could still retrieve old memories.
HM had lost what has later been named
episodic memory (Tulving and Markowitch
1998), referring to our ability to remember
self-experienced events. There is no direct
evidence that place cells are coding episodic
memory. However, place cells can encode
not only for the current spatial location, but
also where the animal has just been and
where it is going next (Ferbinteanu and
Shapiro, 2003). The past and present may
also be overlapping in time in place cells
when animals are rapidly tele-transported
between two physical different
environments (Jezek et al., 2011). An
encoding of places in the past and present
might allow the brain to remember
temporally ordered representations of
events, like in the episodic memory.

After a memory has been encoded, the
memory undergoes further consolidation,
e.g. during sleep. Ensemble recording with
multi-electrodes in sleeping animals has
made possible the study of how memories
of spatial routes achieved during active
navigation are consolidated. Groups of place
cells that are activated in a particular
sequence during the behaviour display the
same sequence of activation in episodes
during the subsequent sleep (Wilson and
McNaughton, 1994). This replay of place cell
activity during sleep may be a memory


consolidation mechanism, where the
memory is eventually stored in cortical
structures.

Together the activity of place cells may be
used both to define the position in the
environment at any given time, and also to
remember past experiences of the
environment. Maybe related to this notion is
the findings that the hippocampus of London
taxi drivers, which undergoes extensive
training to learn how to navigate between
thousands of places in the city without a
map, grew during the year long training
period and that the taxi drivers after this
training had significantly larger hippocampal
volume than control subjects (Magurie et al.
2000, Woollett and Maguire, 2011).

Relevance for humans and medicine

Brain disorders are the most common cause
of disability and despite the major impact on
people’s life and on the society, there is no
effective way to prevent or cure most of
these disorders. The episodic memory is
affected in several brain disorders, including
dementia and Alzheimer’s disease. A better
understanding of neural mechanisms
underlying spatial memory is therefore
important, and the discoveries of place and
grid cells have been a major leap forward to
advance this endeavour. O’Keefe and co-
workers have showed in a mouse model of
Alzheimer’s disease that the degradation of
place fields correlated with the deterioration
of the animals’ spatial memory (Cacucci et
al., 2008). There is no immediate translation
of such results to clinical research or practice.
However, the hippocampal formation is one
of the first structures to be affected in
Alzheimer’s disease and knowledge about
the brain’s navigational system might help
understand the cognitive decline seen in
patients with this diseases.

Conclusions

The discoveries of place and grid cells by
John O’Keefe, May-Britt Moser and Edvard I.
Moser present a paradigm shift in our
understanding of how ensembles of
specialized cells work together to execute
higher cognitive functions. The discoveries
have profoundly promoted new research
with grid and place cell systems now found
in many mammals, including humans.
Studies of the navigation system have
opened new avenues for studying how
cognitive processes are computed in the
brain.

Ole Kiehn and Hans Forssberg

Karolinska Institutet

Ole Kiehn, MD, PhD

Professor of Neuroscience, Karolinska Institutet

Member of the Nobel Committee

Member of the Nobel Assembly

Hans Forssberg, MD, PhD

Professor of Neuroscience , Karolinska Institutet

Adjunct Member of the Nobel Committee

Member of the Nobel Assembly

Illustrations: Mattias Karlen


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