I am pleased to present this year's proceedings of the
M.R. Bauer Foundation Colloquium Series, Scientific Retreat,
and Distinguished Guest Lecturer Series at Brandeis University's
Volen National Center for Complex Systems. The generous
support of the M.R. Bauer Foundation for these programs
is now in its ninth year, and it has enabled the Volen Center
to bring neuroscientists carrying out some of the most interesting
work in the field to campus. The lectures and informal interactions
that took place in the last year facilitated contacts among
Brandeis's faculty and students with leading practitioners
from the United States, Britain, Canada, Israel, and Switzerland-reflecting
the international community of neuroscientists. The following
proceedings describe, I believe, the excitement created
by many of the new investigations in key areas of neuroscience.
My colleagues at the Volen National Center join me in conveying
our sincere thanks to the M.R. Bauer Foundation for its
uninterrupted support, which has made these visits possible.
The M.R. Bauer Colloquium Series hosted seven speakers
in 2002-03. Many of the talks focused on movement, spatial
orientation, and decision-making. Michael
Graziano, Ph.D., from Princeton University's Department
of Psychology proposed that the motor cortex does not contain
a map of the muscles, as had been previously believed, but
rather a "map" of the space towards which movements are
directed. He has found that different regions in the brain,
especially the primary motor and premotor cortex, control
different types of actions in different spatial regions.
Paul Glimcher, Ph.D.,
from New York University's Center for Neural Science, reviewed
recent findings on the computational architecture for decision-making,
and suggested that a mathematical framework based in current
economic theory offers the "critical computational tool"
for understanding the neural basis of human and animal decision-making.
Using robotic modeling, Arthur
Prochazka, M.D., a member of the University of Alberta's
Division of Neuroscience, addressed one of the big unresolved
questions in motor control physiology-do simple reflex pathways,
such as the pathway underlying the tendon jerk, make a significant
contribution to the control of movement? His answer is that
reflexes can rescue a collapsing gait pattern, if the underlying
activity is weak, but they are not likely to do more than
change the body's attitude during movement—for example,
in stretching to tip-toe—if the underlying activity
is strong. Efforts to understand the neurobiology of movement
bring together work that spans molecules to behavior. That
important theme was taken up by the two Bauer Distinguished
Guest Lecturers: Rüdiger Wehner, Ph.D., and Michael
Bate, Ph.D., as described below.
Other speakers in the Colloquium Series addressed the most
recent important findings on synaptic plasticity, or the
brain's ability to reshape and rewire itself, for learning
and memory. Neal Waxham,
Ph.D., from the University of Texas Medical School's Department
of Neurobiology and Anatomy, used three-dimensional structural
analysis and live cell imaging to investigate the role of
a key enzyme, CaM-kinase 11, in synaptic plasticity. He
is seeking to pinpoint the temporal and spatial changes
that occur when this enzyme is locked into the synapse,
as new information is stored. Catherine
Dulac, Ph.D., from Harvard University's Department
of Molecular and Cellular Biology, described her work on
pheromone detection, linking genes with behavior. Pheromones,
which are detected by a structure in the nose called the
vomeronasal organ, signal the sex and dominance of animals.
Dulac estimated that the receptor gene families contain
as many as 400 to 500 pheromone receptors, which are divided
into distinct subgroups, far exceeding earlier estimates.
Her work suggests that pheromone detection involves a remarkable
molecular and cellular complexity. Haim
Sompolinsky, Ph.D., from the Racah Institute of
Physics at the Hebrew University of Jerusalem, spoke about
the balance that neural networks in the cortex achieve between
excitation and inhibition. Using statistical physics to
look at the way in which network architecture, neural dynamics,
and computation interact, Sompolinsky examined the cooperative
aspects of information processing in the brain.
Now in its fifth year, the M.R. Bauer Distinguished Guest
Lecturer Series brought two outstanding scientists to campus
in 2002-03. Rüdiger Wehner,
Ph.D., is professor and chair of the Department of Zoology
and director of the Institute of Zoology at the University
of Zürich in Switzerland. In his major work on ants,
Wehner is trying to answer a general question: How can a
tiny brain weighing about one-tenth of a milligram solve
complex computational tasks such as navigating in a featureless
desert? Wehner discovered that special photoreceptor cells
along the top of the ant's eye are tuned to the polarized
ultraviolet light of the sun. The pattern of polarized sunlight
changes in color and geometry throughout the day as the
sun changes position, giving the ants a "map" by which they
can navigate. Furthermore, Wehner found that only three
neurons integrate information from the photoreceptor cells,
and these neurons do not react to light intensity, only
to the vector orientation of light. Each point of the compass
is defined for the ant by a particular response ratio of
the three neurons (analogous to the human response to the
three basic colors). Therefore, the neural network underlying
the ant's navigation system may be similar to the human
neural network for color. The study of the ant's navigation
system shows that its brain is organized in modules or systems,
a principle that has been conserved by evolution in creatures
ranging from ants to humans. Neuroscientists refer to the
notion of "modularity" when they talk about how the brain
is organized into 5 distinct but interacting systems. In
the case of ants, "modularity" is seen in high-level tasks
that can be accomplished by lower-level solutions built
into separate parts or modules of the brain.
The year's second M. R. Bauer Distinguished Guest Lecturer
was Michael Bate, Ph.D.,
the Royal Society Professor of Developmental Neurobiology
at the University of Cambridge in England. Bate's work focuses
on the neuromuscular juncture during early development.
He is especially concerned with the way in which the machinery
underlying coordinated movement is assembled in the embryo.
In part, this interest involves understanding how neuron
motor circuits are generated and then begin to function.
In the earliest developmental stages, how do nerve cells
know how to make the right connections with the appropriate
muscles? One of the important findings of Bate's work is
that the motor system in the fruit fly is constructed without
the need for sensory input. Bate also addresses how the
cells of the motorneuron system are organized. The dendrites
of these cells, or the branches of neurons that receive
synaptic inputs in the central nervous system, are organized
in a highly predictable spatial array that corresponds to
the pattern of muscles on the periphery. Scientists call
this a "myotopic map," which suggests evidence of an active
process that causes dendrites of nerve cells to grow into
or target specialized areas during early development. Again,
through a series of experiments, Bate shows that the map
forms even without input from muscles. It therefore appears
to be an autonomous property of motorneurons and has nothing
to do with the periphery. This evidence provides just fragmentary
glimpses of the way that the motor system is built, but
these insights allow us to make a reasonable estimate of
the process for the first time.
The 2003 Volen Center Retreat, sponsored by the M.R. Bauer
Foundation, examined "Interesting Systems." For the first
time, the Retreat, which took place on March 3, 2003, was
held at the New England Aquarium in Boston. Eve
Marder, Ph.D., the Victor and Gwendolyn Beinfield
Professor of Neuroscience at Brandeis, took up a question
later addressed by Sompolinsky in the Colloquium Series—how
the stability of complex neural circuits is maintained during
developmental growth. Her work, based on experimental and
computational approaches, is designed to explain how cellular
and circuit homeostasis occurs in the presence of cellular
plasticity. Using experimental results from the crustacean
stomatogastric nervous system, Marder demonstrated that
the long-term maintenance of stable neural circuit behavior
requires the coordinated tuning of both intrinsic membrane
properties (the number and kind of ion channels that provide
electrical excitability) and inhibitory synapses (the connections
between neurons involved in cellular plasticity). Tim
Hickey, Ph.D., professor of computer science at
Brandeis, presented a new approach to studying nonlinear
systems. By using interval arithmetic constraints, he is
seeking to make "provably correct" inferences about the
parameters of complex mathematical systems. Hickey is currently
testing the technique on hybrid systems in which a digital
controller interacts with the physical environment. Complex
neural assemblies may offer, in Hickey's words, interesting
non-linear case studies for the solver. Robert
Malenka, Ph.D., from Stanford University's Department
of Psychiatry and Behavioral Sciences, provided an overview
of synaptic plasticity, which he defined as the ability
of experience to modify the organization and behavior of
neural circuits in the brain. Malenka described synaptic
plasticity as a complex system, in which its two best understood
forms, long-term potentiation (a long-lasting strengthening
of a synapse) and long- term depression (a corresponding
weakening of a synapse), are caused by different patterns
of neural activity. He suggested that synaptic plasticity
might also play an important role in the development of
pathological behaviors, such as addiction. Michael
Kahana, Ph.D., associate professor of psychology
at Brandeis, described experiments in spatial navigational
memory he conducted with epileptic patients who were undergoing
invasive monitoring to identify seizure points in the brain
for surgery. By playing a game in which the patients explored
a virtual space, Kahana recorded from single neurons in
various parts of the brain in order to show that the hippocampus
is specialized for spatial position while the parahippocampus
is specialized for spatial views. Kahana's work fits especially
well with the research of Graziano and Wehner, who have
demonstrated the modularity of the brain in spatial navigation.
Xiao-Jing Wang, Ph.D., associate
professor of physics at Brandeis, spoke about modeling studies
he has conducted on the mechanisms of working memory and
decision making. A major challenge for neuroscientists has
been to understand the cellular and synaptic mechanisms
of the circuits in the cortex of the brain. In order to
maintain working memory, the brain has to convert a transient
pulse-like impulse into an ongoing activity that can be
self-sustained over a much longer time. Wang's computer
modeling of this process shows a "slow reverberation" characteristic
of the neural circuits that create human cognition.
Over the past nine years, the M. R. Bauer Foundation Colloquium
and Scientific Retreat have helped to promote the exchange
of ideas and new methodologies, and, in general, to advance
the study of neuroscience. In the past five years, the M.R.
Bauer Distinguished Guest Lecturer Series has brought some
of the most accomplished neuroscientists in the world to
the University. Both programs have created a strong sense
of community among Brandeis's scientists and the visitors
from other institutions. Our faculty and students have benefited
tremendously from their interactions with the Bauer Colloquium
speakers and Distinguished Guest Lecturers, and these visitors
in turn have taken away a strong sense of the exciting research
and learning at the Volen Center. This booklet represents
an important part of the Volen Center's effort to reach
out to neuroscientists in the broader community in order
to make this work more widely known and continue to facilitate
scientific collaboration and discussions. It is with great
pleasure that I recognize the support of the M.R. Bauer
Foundation for making these activities possible through
its foresight and generosity.
Arthur Wingfield, D.Phil.
Nancy Lurie Marks Professor of Neuroscience and
Director, Volen National Center for Complex Systems
