How Neurons TeamUp To Recognize Patterns, Science 
One of the big open questions for the next millennium is
how the brain uses neurons to represent decisions, perceptions,
emotions and all the other things we can do with our brains. Some
claim that it is impossible at all that neuronal activity alone
can explain consciousness.
After the discovery of neurons with very specific response to
very specific sensory input (e.g. different images that somehow
represent a person looking at something on the floor) the
existence of "grandmother neurons" was postulated: there exist a
single neuron (out of the tens to hundreds of billions of neurons)
in the brain that will become active only if you see (or hear or
think of) your grandmother. That view is similar to that of the
brain as a digital computer where all bits of information are
stored at well-defined addresses on a chip. Experimental evidence
does not support this position. For instance Walter Freeman could
show that in the area of the rabbit brain that responds to
different odors that there are not different neurons for each
smell. Instead different collections (assemblies) of neurons
become active every time the animal smells a familiar odor. It
seems that these assemblies themselves change over the course of
time. Note, however, that all of these effects are very small and
buried in the chaos of spontaneous neuronal activity.
A group of scientist at the Weizman institute in Israel has
developed a technique to visualize brain activity directly with
the help of dyes that change their color under the influence of
the tiny electrical fields that are produced by the brain. In this
way they could observe the formation of neuronal cell assemblies
in cats in response to moving optical stimuli. In their current
paper they undergo a very detailed and careful data analysis to
link the activity of individual neurons to that of the cell
assembly. They could very elegantly establish a "Preferred
Cortical State (PCS)" for each neuron studied. It is defined as an
activity state of the brain (or neuronal assembly) for which the
given neuron shows maximum activity; it is in resonance with its
assembly.
The consequences of this finding is fascinating: For instance
Tsodyks et al. could show that brain states similar to the
neuron's PCS are generated intermittently and the individual
neuron will respond with an enhanced activity with or without a
stimulus. In a way it seems that the brain is spontaneously
browsing through a number of (expected?) states and if the
external stimulus actually happens it can rapidly switch to the
new state.
This phenomenon of "readiness-by-anticipation" is known for the
auditory system. It makes evolutionary sense because it shortens
the response time to visual stimuli and that can be crucial for
the question of eating or being eaten.
Linking
Spontaneous Activity of Single Cortical Neurons and the
Underlying Functional
Architecture, M. Tsodyks,
T. Kenet, A. Grinvald, A. Arieli, Science, Volume 286,
Number 5446 Issue of 3 Dec 1999, pp. 1943 - 1946
-
The earth climate system is certainly one of
the complex systems on our planet with the most severe impact on our
lives. The complex interactions of the atmosphere with factors like
the oceans, ice-shields, and of course human activity leads to and
modifies self-organized, large-scale coherent patterns like
hurricanes and the El Nino oscillation. Several articles in different
journals discuss some of the recent findings into the complexity of
climate dynamics. One of the most dramatic and erratic change
patterns of terrestrial climate are the occurrence of ice ages in the
northern hemisphere. There are a number of factors that can cause
transitions between ice ages and inter-glacial periods. One of them
could be the Arctic Oscillation (AO) an erratic (chaotic?)
oscillation of atmospheric pressure systems over the North Pole.
Another self-organized structure with significant importance
especially for the climate in Northern Europe is the "North Atlantic"
conveyor belt. It is primarily powered by cold seawater that is
formed in the North Atlantic. It because it is more dense it sinks to
the bottom of the ocean. The displaced water forms a deep ocean
current going South. There it displaces warm tropical surface water
that flows back up North (e.g. as the "Gulf Stream") and closes the
circle. If for some reason the conveyor belt slows down it will cause
a significant drop in temperature in the North and a raise in
tropical sea-surface temperatures in the South. The resulting larger
temperature difference in the atmosphere will in turn create wind and
cloud patterns that can either weaken (negative feedback) or
strengthen (positive feedback) of the weakened conveyor belt.
The team of C.
Ruehlemann et al. did a careful investigation into the history of
past sea surface temperatures in the Northern Atlantic. They wanted
to find out if climate changes happened uniformly over the Atlantic
or if there was indeed a cooling in the North while there was a
warming in the South. The first option they identified with
greenhouse gases the second one with a breakdown of the conveyor
belt. They could provide convincing evidence that indeed the conveyor
belt action was a good indicator for climate change. Is this an
argument against greenhouse gases as contributing factors for climate
change? As the primary cause that makes the conveyor belt stop the
authors mention fresh surface water in the North Atlantic. Since cold
fresh water is not as heavy as cold salt water the surface water will
not sink to the bottom of the ocean and the primary driving force has
vanished.
C. Ruehlemann
et al. did not discuss where the fresh surface water was coming
from. R.A.
Kerr mentions that runoff from melting sea ice could be one large
freshwater source. Sea ice has been melting at the alarming rate of
15% per decade. Arctic ice has lost 40% of its volume over the past
30 years. Instead of an average thickness of 3.1 meter arctic ice is
currently down to about 1.6 meter. Changes in the temperature could
have caused changes in storm tracks, therefore changes in cloud
coverage and therefore changes in precipitation patterns. Which in
turn will affect the sea ice runoff.
K.Y.Vinnikov
et al. have done large-scale computer simulations of the chaotic
fluctuations of climate change over a period of 5000 years. They
conclude from their results that the chance that the current sea ice
meltdown is just a large natural swing that will correct itself after
a while is 1:1000.
Therefore it is predictable when at the
current rate all arctic ice cover will be gone. The fourfold change
in albedo from white ice to black water will induce a correspondingly
increased heating of the surface water in Polar Regions. This will in
turn reduce the mixing of surface and deep water, which means that
the oceans will not act as CO2 and heat reservoir.
All these complex feedback loops are classical
ingredients of complex systems. The challenge will be to apply
methods from complexity theory to attack the problem. Will control of
chaos applied to geo-engineering help to get the conveyor belt
jump-started again?
1.
Arctic
Thawing May Jolt Sea's Climate
Belt, William K. Stevens,
NY Times, December 7, 1999
2. Will
the Arctic Ocean Lose All Its
Ice? Richard A. Kerr,
Science, Volume 286, Number 5446 Issue of 3
Dec 1999, p 1828,
3.
Global
Warming and Northern Hemisphere Sea Ice
Extent, Konstantin Y.
Vinnikov, Alan Robock, Ronald J. Stouffer, John E. Walsh,
Claire L. Parkinson, Donald J. Cavalieri, John F. B.
Mitchell, Donald Garrett, Victor F. Zakharov, Science,
Volume 286, Number 5446 Issue of 3 Dec 1999, pp. 1934
- 1937,
4.
Warming
of the tropical Atlantic Ocean and slowdown of
thermohaline circulation during the last
deglaciation
Carsten Rühlemann, Stefan Mulitza,
Peter J. Müller,
Gerold Wefer & Rainer Zahn,
Nature 402, 511 - 514 (1999),
Predicting the Next Move of Flu Viruses, Science
Biology does not have the reputation of being a terribly
predictive science. Arrogant physicists even joke that biological
research consists of replacing a mystery by a miracle. But
biological systems are intrinsically complex since they typically
evolve and adapt. And me know already from simple, non-linear,
iterative function systems and cellular automata that it is
basically impossible to predict how the behavior of a system will
change in response to a modification of its dynamical rules.
One of the most visible examples of this
problem is the common flu: Apparently it is easier to send a man
to the moon than finding a cure for the common cold. While the
moon doesn't try to hide or change its orbit the influenza virus
developed a whole bag of tricks to fool our immune system.
For instance the influenza A virus has
developed a stealth technology to hide from our immune system so
that it has a greater chance to spread every flu season before it
gets detected. Also immunization based on last year's flu is
largely ineffective because the virus has already mutated to a new
form that is not recognized by the immune system. Bush and Fitch
studied the mechanism by which influenza A is doing this trick.
The immune system recognizes the virus with the help of a protein
(hemagglutinin), on the surface of the virus. By comparing
different virus generations over a number of years the researchers
could recognize a pattern in how the successful viruses mutated.
They tested their hypothesis over eleven flu seasons and came out
with a highly significant match. That means they have now a
predictive tool to anticipate the virus' next move. That does not
imply that they know what strain of viruses will hit in the next
flu season (certain strains persist for several years) but at
least they have some idea what sort of vaccines to develop to be
ready for the next influenza mutation. It would be interesting to
see if in this biological arms race the virus will be able to
adapt to this move of human science and change its mutation
patterns.
1.Predicting
the Evolution of Human Influenza
A, Robin M. Bush,
1* Catherine A. Bender, 2 Kanta
Subbarao, 2 Nancy J. Cox, 2 Walter
M. Fitch 1, Science, Volume 286, Number
5446 Issue of 3 Dec 1999, pp. 1921 - 1925
2.
Predictive
Evolution, David M.
Hillis, Science, Volume 286, Number 5446 Issue of 3 Dec
1999, pp. 1866 - 1867,
Chaos Theory Helps To Predict Epileptic Seizures, U. Florida
Inspired by an intriguing mathematical
concept known as chaos theory, researchers at the University of
Florida Brain Institute and the Malcom Randall Veterans Affairs
Medical Center in Gainesville have developed a technique for
predicting some types of epileptic seizures minutes to hours
before they begin.
Their work, under development for more than
a decade and now the basis of a U.S. patent application, opens the
door to the creation of implantable devices that can detect signs
a seizure is approaching and deliver medication, or electrical or
magnetic stimulation to try to prevent it.
"We had determined some years ago that
there was a theoretical potential for predicting seizures," said
Dr. J. Chris Sackellares, a VA neurologist and a UF professor of
neurology, neuroscience and biomedical engineering who has been
researching temporal lobe epilepsy with Leonidas D. Iasemidis, a
VA research engineer and UF research assistant professor of
electrical and computer engineering, and neuroscience. "But it has
only been in the past year that we have really been able to
demonstrate that we can do so reliably. And it has only been
recently that we realized that the state of transition to a
seizure could last for many hours."
(…)
The researchers began to suspect in 1988
that the emerging field of chaos science would be able to shed
light on epilepsy. In a nutshell, chaos theory offers a
mathematical approach for seeing a kind of order in events that
previously had appeared to be random. Early in the 1990s, the
approach enabled Sackellares and Iasemidis to be the first to
identify the existence of a pre-seizure transition period.
In their early research the scientists were
looking for such transitions to occur seconds to minutes before a
seizure began. But in the past year, by analyzing electrical
activity in the brain recorded for a 10-day period, they have
identified a warning stage developing anywhere from minutes to
many hours ahead of time.
Their technique involves using
sophisticated mathematical formulas to sort through the brain's
complex electrical signals, which can be recorded by
electroencephalograms, or EEGs. The scientists theorize that a
seizure's function is to correct a neural system gone awry. Though
it may sound counterintuitive, a buildup of organized, harmonious
signals is what apparently needs to be fixed to return the brain
to its naturally chaotic state.
To predict seizures, Iasemidis, who directs
the Gainesville VA's Brain Dynamics Laboratory, and Sackellares
look for signs of communication between the site where a patient's
seizure begins and elsewhere in the brain. When an increasing
number of electrode pairs begin oscillating together during an
EEG, it signals a seizure is on its way.
(…)
Iasemidis noted that their goal is to be
able to identify a window of opportunity for preventing seizures.
"Predicting exactly when a seizure will occur is not the main
question," he said. "We're interested to see if we can knock the
system out of its route to the seizure. We'd like to see if we can
intervene with either electricity or medication to try to get the
system to reset itself right at the beginning of the buildup of
the pre-seizure transition.
(…)
But Sackellares and Iasemidis say it is
realistic to think that implantable devices can be developed to
detect the preseizure state and automatically act to thwart it.
They noted that such devices have been developed for other
conditions, including diabetes.
A scientist who collaborated with
Sackellares and Iasemidis in the early 1990s said he had been
skeptical back then that the computational difficulties of the
line of research could be overcome.
"It seems that they have been able to press
ahead and realize their long time-dream of making the methods
associated with chaos theory practical," said William J. Williams,
a professor of electrical and biomedical engineering and computer
science at the University of Michigan. "No one else has pursued
this direction of research so persistently in order to achieve
such an advanced understanding of epilepsy. The practical
applications of their work will likely have a lasting beneficial
effect on many people who suffer from epilepsy.
University
Of Florida Health Science
Center,
Victoria White , Office Of Public
Information
Another Miraculous Property of Water, Nature
It is no accident that researchers look for signs of
water on other planets to determine the possibility for life. Its
amazing properties make water indeed a very special liquid.
Woutersen and Bakker added another miracle property to the list
that confirms that water is indeed the perfect environment for
life-like processes. They could show that water can act as
extremely fast conductor of energetic states between and within
molecules especially bio-molecules. Many organic molecules have OH
groups (i.e. pairs of an oxygen atom connected to a hydrogen)
attached to them. Their structure and state determine many of the
chemical properties of the molecule.
The OH groups also acts as a springs that
can store energy in the form of stretch-vibrations. Exactly which
of the many OH groups in a large bio-molecule are in such a
vibration mode and how much energy is stored determines which
reactions will take place and which ones will be suppressed.
Therefore the fast and effective transfer of energy between
different OH vibrations can be crucial for many of the central
processes in living systems. Once excited an OH vibration looses
its energy already after about 740 femto-seconds. That is more
than a thousand times shorter than the time it takes the fastest
Pentium chip to complete one elementary operation. During that
time the OH spring oscillates less than a hundred times.
With the help of different mixtures of
light and heavy water the researchers could demonstrate the
because of the special properties of water it can transfer the
energy stored in these vibrations fast enough to prevent it from
being dissipated. Although the experimental evidence is quite
convincing that the energy transfer happens it is still not clear
how exactly this works. It seems clear, however, that non-linear
resonance phenomena are essential in this process.
Resonant
intermolecular transfer of vibrational energy in liquid
water,
Sander Woutersen, Huib J. Bakker,
Nature 402, 507 - 509 (1999)
Physicists and Astronomers Prepare for a Data Flood, Science
The spread of the Internet spawned an increasing number
of publications that speculate about a new evolutionary level of
organization of humans, networked together via the Internet. One
question naturally comes up about the need for such a
superstructure. What problems could be solved that cannot be
solved by traditional team working?
The paper by Mark Sincell might provide one
answer: A new generation of data-recording devices in science and
especially in particle physics and astronomy will provide a stream
(better: torrent) of information that goes orders of magnitudes
beyond ordinary human experiences. The planned Large Hadron
Collider at CERN in Geneva will write data to a disk-based
database at a rate of 100MB per second up to a total of 100
petabytes = 1017 bytes that is the equivalent of about 10 million
feature length movies (in DVD resolution). Or, according to Arthur
C. Clark's science fiction novel "3001", the totality of all
experiences of a human being during the whole life span i.e. an
old person's brain content if that person had perfect memory.
Although particle physics is notorious for
collecting tons of data in order to detect a handful of
"interesting events" -like the trace of a Higgs particle- this
example demonstrates the domains of information processing that
will be happening in the next millennium.
Astronomers are expected to collect data
about 200 million galaxies in the amount of a mere 40 Terabytes.
They are also known to actually do something with their data like
collecting statistics and detecting patterns in their positions
and motions. Storing the data at a central location and
downloading them to individual users (today's standard
client-server model) is not feasible for that amount of data. A
new, hierarchical structure in the data storage organization will
move data closer to the user in several tiers depending on the
actual use patterns. The concept of linking data storage with
usage is not new: memories in the brain are stored in a way that
critically depends on usage frequencies.
Because of the globally accessible enormous
quantities of information some researchers predict that new
discoveries will emerge with the help of automated search software
that would have been beyond the capabilities of humans.
Physicists
and Astronomers Prepare for a Data
Flood, Mark Sincell,
Science, Volume 286, Number 5446 Issue of 3 Dec 1999, pp.
1840 - 1841
The DNA sequence of human chromosome 22, Nature
The human genome project is to biology what high energy
physics is to physics: Big Science where the length of the list of
authors of becomes a major fraction of the publication of the
research results.
To decode the software that assembles us
humans is an ongoing global collaboration that predictably will be
finished in the very early part of the third millennium. This
predictability of the research results is also a feature common
with elementary particle physics where one can predict the date at
which enough events will be collected to be published in the first
rate journals.
I. Dunham and 215 collaborators succeeded
in decoding chromosome No. 22 (out of 46) consisting of more than
33 million bases, 545 genes, and 134 pseudogenes. It is the first
complete mapping of a human chromosome which covers almost 2% of
the genomic DNA.
This research group used the
"clone-by-clone" approach of two commonly used methods to sequence
the human DNA. It covers piece by piece parts of the DNA and
determines its complete sequence. The alternative is a "shotgun
approach" that sequences much smaller segments selected from the
whole genome.
There are some medical reasons for starting
with chromosome 22: It is the location for a number of human
congenital anomaly disorders including cat eye syndrome and the
schizophrenia susceptibility locus.
The authors call their results an "
operationally complete genomic sequence of a chromosome" but admit
that they were unable to obtain sequence over 11 small gaps using
the available cloning systems but express hope that these gaps
will be closed with improved methods.
All the results are continuously made
available to the public via the Internet: The complete sequence
and analysis is available at (http://www.sanger.ac.uk/HGP/Chr22
and http://www.genome.ou.edu/Chr22.html).
The
DNA sequence of human chromosome
22, I. Dunham
et al, Nature 402, 489 - 495 (1999)
-
The last Scientific American issue of 1999 is
dedicated to a discussion what kind of discoveries can be expected in
the first 50 years of the new millennium. It is quite adequate that
the former editor of one of the most prestigious (and oldest) science
journals of the second millennium, Sir John Maddox of Nature, gives
both a review and a preview of the most fundamental discoveries in
science.
One of the easier forecasts is the completion
of the human genome project with its tremendous implications not only
for medicine but also for the reconstruction of the genetic
reconstruction of the human race. Will it be possible to explain the
transition from great apes (having 48 chromosomes) to humans (only 46
chromosomes) and why only a single species of humans survived?
Maddox sees a second evolution related
fundamental question in the interpretation of the non-coding "junk"
parts of the DNA. It could shed some light on living things in the
"RNA world" that supposedly preceded the "DNA world" we are living in
today. He does not expect, however, that anybody will be able to
build a complete RNA organism within the next 50 years.
Another open fundamental question is that of
the origin of life. Maddox expect that a better understanding of how
solar radiation can interact with molecular cloud in outer space to
form increasingly complex molecules including fullerenes (commonly
known as "buckyballs").
He also expects that biology as a science will
become more predictive and quantitative instead beyond discovering
more "miracle" enzymes with peculiar functions. For instance the
cell-division cycle has been the subject for discovering new enzymes
at a rate of one new enzyme per week but without answering the
questions about how the enzymes which trigger the cell cycle are
triggered.
There is hope that some of the fundamental
questions of brain science will be answered in the next fifty years,
for instance which neuronal processes correspond to the act of making
a decision.
The
Unexpected Science to
Come,
Sir
John Maddox, Scientific
American, Special Issue: What Science will know in 2050,
12/99
Neanderthals Worked Themselves to Death, Discovery News Brief
If we take brain size as a measure for a species'
position on the evolutionary ladder then two completely different
candidates for the top clearly stand out: humans and cetaceans.
One of the most puzzling differences is that only a single species
of humanoids survived a mere few million years of evolution after
they separated from their closest ancestors, the great apes.
Cetaceans, on the other hand, have branched into a large number of
different species, from small dolphins to the largest mammal that
ever inhabited this planet, the Blue Whale. These numerous species
by no means peaceful creatures: dolphins gang up against porpoises
and kill them; killer whales hunt and kill other whales. But in
spite of this they have been able to coexist for tens of millions
of years in basically their current form.
The last surviving sister species of homo
sapiens, the Neanderthals went extinct just a little over 20,000
years ago after having adapted to challenging climate changes over
a period of 250,000 years and after coexisting with modern humans
for thousands of years.
Duke University anthropologist Steven
Churchill thinks that ultimately, the physical costs of their
hunting methods may have been too high for Neanderthals to
survive. Their anatomy was supposed to be less efficient that that
of Cro-Magnons for hunting large animals. Furthermore they might
have lacked the language and strategic planning skills to prevent
extensive periods of famine.
Although these hypotheses have a level of
plausibility it seems unlikely that they fully explain the mystery
of the disappearing Neanderthals.
Neanderthals
Worked Themselves to
Death, Blake Edgar,
Discovery News Brief , 5 Dec. 1999
See also Youngest
Neanderthals Yet Found,
The
Fate of Neandertals
IBM’s new supercomputer, CNN/Reuters
IBM's claim to fame in the area of super-computing in the
past was not so much based on scientific discoveries or
simulations but more in the area of finding the biggest prime
numbers and beating human chess grand-masters.
This might change with the latest IBM
supercomputer -named Blue Gene- that was announced to become fully
operational in about five years. As the name suggests its design
purpose will be in one of the areas of complex systems research:
protein folding (see ComDig
99:beta4.1).
The strategy that IBM follows to achieve a
one quadrillion operations per second (two million times the speed
of the fastest microcomputer today) is not to develop faster
processors but to use current off-the shelf processors and use it
in a massively parallel way.
It is known that this route requires
special demands on software as well as on the problems for which
this speed-up can be achieved. For instance the time to multiply
two numbers will not be much faster on Blue Gene than on four
notebook computer. But for problems like protein folding where the
movement of a large number of atoms have to be tracked
simultaneously it will be possible to distribute the computational
load from the movement of different atoms to different
processors.
IBM’s
new supercomputer,
CNN/Reuters, December 06, 1999: 7:45 a.m.
ET
Ancient origins of nitric oxide signaling in biological systems, PNAS
Complex adaptive systems need efficient communication
among their sub-units or agents such as chemical trails in ant
colonies and electrical nerve pulses in neuronal systems and
brains. Just like parts of the brain show their ancient
evolutionary history it seems that also the signaling methods in
organisms have inherited some pathway from ancient evolutionary
times. Whereas it has been known for a long time that organisms
use hormones (relatively complex proteins) to regulate body
functions and emotional responses it is less known that the simple
molecule nitric oxide (NO, consisting only of the two atoms
nitrogen and oxygen, both abundant in our atmosphere) plays an
astounding signaling role in different systems of our body. For
instance it helps to keep our blood pressure constant, to stop
bleeding, and even to transmit nerve signals in a chemical and not
electrical manner. It also plays an important role in our immune
system by contributing to the activation of cellular defenses
against pathogens. Surprisingly it also is involved in a similar
function for plants. Furthermore NO helps the blood hemoglobin to
deliver oxygen to tissue that is in need of it. It does that by
causing blood vessels to dilate and thereby increase the supply
with oxygen-rich hemoglobin. Durner et al. were able to analyze in
great detail the chemical processes that make these functions
possible. The importance of NO for controlling biological
functions is also supported by the fact that a special enzyme
exists that will produce new NO in animals. In spite of the
functional similarities with plants, however, it was not possible
so far to also identify a similar enzyme produced by plants.
Ancient
origins of nitric oxide signaling in biological
systems,
Jörg Durner, Andrew J. Gow, Jonathan S. Stamler, and
Jane Glazebrook , PNAS, Vol. 96, Issue 25,
14206-14207, December 7, 1999
Immortality and Cancer, PNAS
The age of a cell can be determined from the length of
its telomeres (the end section of a chromosome, composed of
several hundred base pairs): Every cell division shortens the
telomeres until cell undergo apoptosis and die. The enzyme
telomerase can lengthen the telomeres again and extend cell life
theoretically making them immortal.
Using telomerase as a life prolonging agent
has its risks: It is known that telomerase is especially active in
cancer cells basically allowing them to continue dividing without
limit. Herbert et al. studied how agents that inhibit can indeed
cause cancer cells to age and eventually die. If telomerase is
activated for aging cancer cells the process is reverted, the
telomeres grow back to their original length and the cell is
immortal again.
The telomere age of cells has an
interesting consequence for cloning: It turns out that clone
organisms are born with the cell-age of the donor organism. That
puts a damper on the hope that cloning could be used to achieve
immortality: the cells of the cloned baby are just as old as those
of the parent.
Inhibition
of human telomerase in immortal human cells leads to
progressive telomere shortening and cell
death, B.-S. Herbert, A.
E. Pitts, S. I. Baker, S. E. Hamilton, W E. Wright, J. W.
Shay, and D. R. Corey, PNAS, Vol. 96, Issue 25,
14276-14281, December 7, 1999
