Niche Construction, Biological Evolution and Cultural Change, BBS 
Abstract: We propose a model to map the causal
pathways relating biological evolution to cultural change.
Building on conventional evolutionary theory, the model emphasises
the capacity of organisms to modify sources of natural selection
in their environment (niche construction); the evolutionary
dynamic can also be broadened to incorporate ontogenetic and
cultural processes, with phenotypes playing a much more active
role in evolution. The model sheds light on hominid evolution, the
evolution of culture, altruism and cooperation. Culture amplifies
the capacity of human beings to modify sources of natural
selection in their environments to the point where that capacity
raises some new questions about the processes of human
adaptation.
Excerpt: The relationship between genetic evolution and
culture raises two causal issues: The first is concerned with the
extent to which contemporary human cultures are constrained or
directed by our biological evolutionary heritage. The second
explores whether hominid genetic evolution has itself been
influenced by cultural activities. We contend that these issues
are inextricably tied, and argue that the significance of
evolutionary theory to the human sciences cannot be fully
appreciated without a more complete understanding of how
phenotypes in general, and human beings in particular, modify
significant sources of selection in their environments, thereby
codirecting subsequent biological evolution. Our principal goal is
to delineate and explore the interactions between biological
evolution and cultural change."
One example of gene-culture co-evolution is the fact that the
cultural practice of dairy farming in the past has selected for
lactose tolerance in humans. A current "cultural practice" mostly
in Asia is the parental preference for boys over girls. Sex
selective abortions as well as sex-biased parental investment have
led to significant increases in male/female sex ratios .
Heritability At The Ecosystem Level, PNAS
Excerpt: In the first article of the first volume
of Annual Review of Ecology and Systematics, Lewontin
(1)
points out that any level of organization that can be grouped into
a population of units has the potential to evolve by natural
selection. Evolution by natural selection has been seen in
experimental studies of individual and group selection, and now
Swenson et al. (2)
have demonstrated that selection acting at the level of the
ecosystem can cause evolutionary change.
Lewontin describes the three properties of a population that
are necessary and sufficient for evolution by natural selection to
occur. Briefly, these properties are that (i) there must be
phenotypic variation, (ii) the different phenotypic variants must
be associated with different fitnesses, and (iii) fitness must be
heritable. Lewontin goes on to explain that, in principle, any
level of biological organization can exhibit these three
properties; thus, any level of organization that can be grouped
into a population of units has the potential to evolve by natural
selection. He then concludes that it is unlikely that natural
selection acting above the level of the individual will be an
important evolutionary force, in part on the grounds that it is
the higher level units that are unlikely to exhibit heritability
of fitness. (...)
Genetic Diversity And Disease Control In Rice, Nature
Excerpt: The
results of Chinese field trials reinforce the accepted scientific
wisdom that planting different varieties of a crop in the same
field holds down the spread of certain diseases and improves
yields. And this time researchers seem to have convinced farmers,
too.
Zhu Youyong, a plant pathologist at the Phytopathology
Laboratory of Yunnan Province at Yunnan Agricultural University in
Kunming, China, and colleagues report in the 17 August issue of
Nature on a 2-year experiment that involved mixing two varieties
of rice in the same field. Their work, involving thousands of
local rice farmers, found an 18% rise in overall productivity,
including greater profits for a premium-priced variety that is
particularly susceptible to rice blast from a fungus.
Excerpt:
Crop heterogeneity is a possible solution to the vulnerability of
monocultured crops to disease1-3. Both theory4 and observation2, 3
indicate that genetic heterogeneity provides greater disease
suppression when used over large areas, though experimental data
are lacking. Here we report a unique cooperation among farmers,
researchers and extension personnel in Yunnan Province,
China-genetically diversified rice crops were planted in all the
rice fields in five townships in 1998 and ten townships in
1999.
- Genetic
Diversity And Disease Control In
Rice, Youyong Zhu,
Hairu Chen, Jinghua Fan, Yunyue Wang, Yan Li, Jianbing
Chen, Jinxiang Fan, Shisheng Yang, Lingping Hu, Hei
Leung, Tom W. Mew, Paul S. Teng, Zonghua Wang &
Christopher C. Mundt, Nature 406, 718 - 722
(2000)
- Variety
Spices Up Chinese Rice
Yields Dennis Normile,
Science, Vol 289, Nor 5482, 18 Aug 2000, pp.
1122-1123
Learning Motor Synergies Makes Use Of Information On Muscular Load, Learn. Mem.
Abstract: Prism adaptation, a form of procedural
learning, requires the integration of visual and motor information
for its proper acquisition. Although the role of the visual
feedback has begun to be understood, the nature of the motor
information necessary for the development of the adaptation
remains unknown. In this work we have tested the idea that
modifying the arm load at different stages of the adaptation
process, and the ensuing change of motor information perceived by
the subjects, would modify the final properties of the adaptation.
We trained a set of subjects to throw balls to a target while
wearing prism glasses and varied the weight of their arms at
different time points during the task. We observed that the
acquisition of the adaptation was not affected by the change in
load. However, its persistence (i.e., the aftereffect) was reduced
when tested under a weight condition different from the training
trials. Furthermore, when the training weight conditions were
restored later during testing, a second, late aftereffect was
unmasked, suggesting that the missing aftereffect did not
disappear but had remained latent. Our results show that the
internal representation of a motor memory incorporates information
about load conditions and that the memory stored under a specific
weight condition can be fully retrieved only when the original
training condition is restored.
Information Shortcuts In Neurons, PNAS
Abstract: Neocortical pyramidal neurons have
extensive axonal arborizations that make thousands of synapses.
Action potentials can invade these arbors and cause calcium influx
that is required for neurotransmitter release and excitation of
postsynaptic targets. Thus, the regulation of action potential
invasion in axonal branches might shape the spread of excitation
in cortical neural networks. To measure the reliability and extent
of action potential invasion into axonal arbors, we have used
two-photon excitation laser scanning microscopy to directly image
action-potential-mediated calcium influx in single varicosities of
layer 2/3 pyramidal neurons in acute brain slices. Our data show
that single action potentials or bursts of action potentials
reliably invade axonal arbors over a range of developmental ages
(postnatal 10-24 days) and temperatures (24°C-30°C).
Hyperpolarizing current steps preceding action potential
initiation, protocols that had previously been observed to produce
failures of action potential propagation in cultured preparations,
were ineffective in modulating the spread of action potentials in
acute slices. Our data show that action potentials reliably invade
the axonal arbors of neocortical pyramidal neurons. Failures in
synaptic transmission must therefore originate downstream of
action potential invasion. We also explored the function of
modulators that inhibit presynaptic calcium influx. Consistent
with previous studies, we find that adenosine reduces
action-potential-mediated calcium influx in presynaptic terminals.
This reduction was observed in all terminals tested, suggesting
that some modulatory systems are expressed homogeneously in most
terminals of the same neuron.
Synthesis Of Organs: In Vitro Or In Vivo?, PNAS
Excerpt: With its rapid conceptual leaps,
cell/molecular biology has converged with the accelerating
trajectory of bioengineering, and the outcome of this encounter
suggests that replacement of organs is either here or not faraway.
Historically, five methods have been used to tackle the problem of
the missing organ: transplantation, which suffers from depletion
of organ donors; autografting, excising part of a patient's organ
to graft and restore organ function in another part of the anatomy
where it is needed more; replacement with a permanent prosthesis,
which turns out not to be permanent at all, requiring revision
surgery after a few to several years of implantation; in vitro
synthesis, a popular research direction, in which an organ is
first largely synthesized in culture and then is implanted; and in
vivo synthesis, which depends on implantation only of the bare
minimum required to induce organ regeneration in situ. The last
two paradigms are commonly referred to collectively as tissue
engineering.
Minimizing Binding Errors Using Learned Conjunctive Features, Neural Comp
Abstract: We have studied some of the design
trade-offs governing visual representations based on spatially
invariant conjunctive feature detectors, with an emphasis on the
susceptibility of such systems to false-positive recognition
errors—Malsburg's classical binding problem. We begin by
deriving an analytical model that makes explicit how recognition
performance is affected by the number of objects that must be
distinguished, the number of features included in the
representation, the complexity of individual objects, and the
clutter load, that is, the amount of visual material in the field
of view in which multiple objects must be simultaneously
recognized, independent of pose, and without explicit
segmentation. Using the domain of text to model object recognition
in cluttered scenes, we show that with corrections for the
nonuniform probability and nonindependence of text features, the
analytical model achieves good fits to measured recognition rates
in simulations involving a wide range of clutter loads, word
sizes, and feature counts. We then introduce a greedy algorithm
for feature learning, derived from the analytical model, which
grows a representation by choosing those conjunctive features that
are most likely to distinguish objects from the cluttered
backgrounds in which they are embedded. We show that the
representations produced by this algorithm are compact,
decorrelated, and heavily weighted toward features of low
conjunctive order. Our results provide a more quantitative basis
for understanding when spatially invariant conjunctive features
can support unambiguous perception in multiobject scenes, and lead
to several insights regarding the properties of visual
representations optimized for specific recognition tasks.
How To Cut Off Blood Supply To Cancer Tissue, Science
"Tumors require a blood supply for growth, and several
cancer therapies now in clinical trial are designed to disrupt
that blood supply by targeting the tumor vasculature. In a
comprehensive analysis, St. Croix et al. (p. 1197;
see the news story by Marx) found that the blood vessels in tumors
and normal tissue show qualitative differences in the expression
of 79 genes. Most of the genes differentially expressed in the
tumor vessels are of unknown function; the majority of the known
genes play a role in extracellular matrix formation. The genes
marking the tumor vessels were expressed in tumors derived from a
variety of tissue types and, importantly, were also expressed in
vessels induced by other pathophysiological states, such as wound
healing."
"Researchers have obtained the most detailed sketch yet of
how cancerous tumors secure the blood supplies that nourish their
growth. On page 1197, a team reports the results of a large-scale
comparison of the genes expressed in the blood vessels of human
colon cancers and of normal colon tissue.
They've found that the gene expression patterns of the two
types of vasculature are distinctly different. The findings could
help researchers develop new anticancer drugs that work by homing
in on the protein products of genes that are overexpressed in
tumor vessels, thus shutting off the growth of blood vessels the
tumor needs to survive."
- Vascular
Signatures, Science,
August 18 2000, 289 (5482)
- Tumor
Angiogenesis: Gene Expression Patterns
Identified, Jean Marx,
Science, Vol. 289, No. 5482, 18 Aug 2000, pp.
1121-1122
- Genes
Expressed in Human Tumor
Endothelium,
Brad St. Croix, Carlo Rago, Victor Velculescu,
Giovanni Traverso, Katharine E. Romans, Elizabeth
Montgomery, Anita Lal, Gregory J. Riggins, Christoph
Lengauer, Bert Vogelstein, Kenneth W. Kinzler,
Science, Vol. 289, No. 5482, 18 Aug 2000, pp.
1197-1202
UCSF Researchers Identify Regulator Of Critical Brain Messenger, Hinting At Therapy, UCSF Press Release/Science Daily
In the dynamic world of the central nervous system,
the neurotransmitter glutamate is a key player, ceaselessly
transmitting critical instructions between nerve cells. Now, UCSF
researchers have identified the protein that transports the
chemical signal to its launch site in nerve cells, offering a
possible new target for treating such diseases as Alzheimer's
disease.
The discovery opens a vast field of potential therapy, for
while glutamate carries out such fundamental processes as sensory
perception, learning and memory, changes in its role contribute to
many brain diseases. The release of too much glutamate causes
excessive excitation in the nervous system that leads to seizures,
contributes to injury after stroke, the perception of pain and
even the destruction of nerve cells associated with
neurodegeneratives diseases, including Alzheimer's disease,
Parkinson's disease and amyotrophic lateral sclerosis (Lou
Gehrig's disease). A drug that blocked the glutamate transporter
from loading glutamate, thus reducing the release of glutamate,
could treat these illnesses.
Alternatively, increasing the amount of glutamate released
from certain nerve cells could improve learning, memory skills and
overall cognitive function. In this case, therapy might simply
involve taking a drug that increases the expression of the gene
that produces the protein transporter. The resulting increased
expression of the protein would enable nerve cells to store and
release more glutamate. (…)
Glutamate, like all neurotransmitters, is a chemical message
released by one nerve cell and targeted at another. Thousands of
glutamate molecules are released from a single cell, prompting a
response in a neighboring cell, which prompts a response in yet
another cell. The millisecond relay between thousands of nerve
cells causes a flurry of activity that prompts the brain to carry
out all fundamental aspects of brain function. (...)
Now, in the August 11 issue of Science, the University of
California, San Francisco researchers report not only that they
have identified the transporter, but that it is a protein that
scientists have thought had a completely different role.
Previously known as brain-specific inorganic phosphate
transporter, the researchers have renamed the protein vesicular
glutamate transporter, or VGLUT1.
"The discovery of the glutamate transporter represents a
major missing component that people have sought for a long time,"
says Edwards. "It is one of the final things that will enable us
to study the basic function of how synapses work."
- UCSF
Researchers Identify Regulator Of Critical Brain
Messenger, Hinting At
Therapy,
UCSF Press Release, 8/10/00
- See also: Science
Daily, 8/18/00
- Long-Sought
Protein Packages
Glutamate, Laura
Helmuth, Science,Vol. 289, No 5481, 11 Aug 2000, pp.
847-849.
- Uptake
Of Glutamate Into Synaptic Vesicles By An Inorganic
Phosphate Transporter ,
Elizabeth E. Bellocchio, Richard J. Reimer, Robert T.
Fremeau Jr., Robert H. Edwards, Science,Vol. 289, No
5481, 11 Aug 2000, pp.957-960
-
Excerpt: A new study by researchers at
Dana-Farber Cancer Institute offers fresh evidence for a theory of
why incidences of certain cancers grow more common as people
age.
The theory is that in tissues that undergo continual
renewal, a process where cells die and are replaced throughout
life, such as those in the breast, skin, prostate, and colon - a
genetic mutation causes some cells to keep dividing even after
their chromosomes have lost their protective protein ends called
telomeres. The result is chromosomes that fuse together in
abnormal ways, creating chaos with cells' genetic programming and
setting them on the path toward cancer.(…)
Normally, mice with flaws in their genetic "brakes" against
cancer develop lymphomas and malignancies known as sarcomas in
bones and connective tissue. In aging humans, however, tumors tend
to arise in "epithelial" cells-cells that regularly die and are
replaced--that line the interior of certain organs.
The DePinho team speculated that reason for this difference
lay in the telomeres. In humans, telomeres shorten each time a
cell divides until they become so short they can no longer protect
the chromosomes from damage. At this point, known as the "Hayflick
limit," the cells normally cease dividing. In some cells, however,
a genetic error enables them to bypass the Hayflick limit and
continue dividing even though their chromosomes are virtually
shorn of telomeres. At this stage, known as "crisis," the cells'
chromosomes begin breaking and fusing in abnormal places.
"When these complex chromosomal rearrangements occur, you
get very rapid gains and losses of genetic information within
cells," lead author Artandi says. "This process, known as
"crisis," gives rise to pre-cancerous cells that begin to form a
primary tumor, but cannot fully develop until telomere function is
restored." At this point, full maturation of the cancer is
achieved by reactivation of the enzyme telomerase, rebuilding and
stabilizing the cells' telomeres -- and allowing continued tumor
cell division and migration within the body.
"We have long known that cancer is associated with age,"
senior author DePinho remarks. "We know it tends to occur in
epithelial cells in older adults, and we know the chromosomal
structure of these cancer cells is very complex: under a
microscope, it looks as though someone threw a grenade into the
nucleus where the chromosomes are located. We wanted to find an
explanation for these phenomena."
The answer would come from studies with mice. In mouse
cells, unlike human cells, the gene for rebuilding telomeres is
always switched "on," so the telomeres don't shorten with each
cell division. This has been thought to explain why mice tend to
develop cancer in different tissues than aging humans do. DePinho
and his colleagues developed a strain of mouse in which, like
humans, the telomere-building gene is shut off. "Essentially, we
engineered the mouse cells to experience 'crisis,' something they
would normally be prevented from doing," DePinho says.
The results were striking. "We saw a dramatic shift in the
types of tumors these animals developed," DePinho continues. "They
much more closely resembled the tumor spectrum found in aged
humans."(...)
- Study
Points To Cell "Crisis" As Key Event In Development Of
Cancer In Older Adults,
Dana-Farber Cancer Institute Press Release, 8/9/00,
Science
Daily
- Telomere
Dysfunction Promotes Non-Reciprocal Translocations And
Epithelial Cancers In
Mice, Steven E.
Artandi, Sandy Chang, Shwu-Luan Lee, Scott Alson,
Geoffrey J. Gottlieb, Lynda Chin & Ronald A.
Depinho, Nature 406, 641 - 645 (2000)
Self-Adjusting Chips To Extend Limits Of Computing Power, U. Rochester/ Daily Science
Excerpt: A team of scientists at the University
of Rochester is undertaking the next step in computing-designing a
chip that reconfigures itself as it runs, adapting to the needs of
software while processing faster and using less power while doing
so. The adaptable chip signals an effort to take full advantage of
the massive processing power that chip makers now deliver to
desktops every day.
David Albonesi, assistant professor of electrical and
computer engineering at the University of Rochester, leads the
team, which has created a model called Complexity-Adaptive
Processing (CAP) that monitors the way a piece of software uses
the microprocessor hardware, and then adapts that hardware
accordingly. The result is a more efficient processor that doesn't
dawdle while running many tasks. Early tests have shown CAP able
to halve the energy consumption of part of the chip while also
improving performance.
"Today's microprocessors are pretty inefficient when
handling a variety of tasks," says Albonesi. "They're designed to
work well overall, but since they're inflexible they can't work as
well as they could for any particular program." (…)
He started to look into certain inefficient parts of a chip,
such as the cache, a kind of storage closet on the chip where
frequently needed information can be stowed and accessed quickly.
Most microprocessors today contain two types of cache, with a
larger, slower cache acting as a backup to a smaller, faster one.
Although the sizes of these caches are fixed in today's
microprocessors, different programs require different sizes to run
most efficiently. Similar to how a thermostat controls an
air-conditioning system, the CAP design monitors the program as it
runs and adjusts the sizes and speeds of the caches as needed,
saving the energy taken to maintain them, and saving the time
taken to track down information inside them.
Along with Albonesi, Eby Friedman, professor of electrical
and computer engineering; Sandhya Dwarkadas, assistant professor
of computer science; and Michael Scott, professor of computer
science, pooled their resources to develop the system further. The
researchers recently received $3 million in funding from the U.S.
Defense Advanced Research Projects Agency to continue the work.
The team has a number of other tricks that it expects will
produce even greater improvements, including changing the value of
"one." Microchips send information by means of "zeros" and "ones,"
with the zeros represented by no voltage, and the ones represented
by a voltage high enough to be detected above the background noise
of electricity flowing through the chip. By reducing such things
as the cache size, the scientists can lower the overall noise in a
particular part of a chip, allowing them to lower the voltage
needed to represent a one and thus saving energy. Like the
changing cache size, this alteration can be done and undone as
needed, millions of times each second, as the processor cranks
along.
The CAP model may be able to save even more energy by
offering ways to switch fewer transistors in the chip between one
and zero, and by slowing down the processor's speed and lowering
the voltage when it detects that a program can get by on less.
Some of today's processors, such as the Pentium III, have the
option of lowering voltage to save battery life on laptops, but
this requires running at a slower speed. The team's design should
allow even longer battery life while computing just as quickly or
faster than today's microchips. (...)
-
Excerpt: In a collaborative study, American and
Brazilian scientists have discovered that hummingbirds, parrots
and songbirds orders of birds that are evolutionarily distant from
one another have evolved remarkably similar brain structures in
order to learn to sing. The finding, reported in the Aug. 10 issue
of Nature, will not only help understand the evolution of song in
birds, but also offer insights into language in humans.
According to Duke University Medical Center neurobiologist
Erich Jarvis, the paper's lead author, while most of the 23 orders
of birds can vocalize, like the rooster that crows, these
vocalizations are not learned but are genetically hardwired
sounds. Only three orders of birds the songbirds, parrots and
hummingbirds have the ability to learn songs from their adult
tutors and repeat them in the right context, said Jarvis. This
type of vocal learning is very similar to the way that humans
learn to speak.
Surprisingly, these singing birds are not closely related to
each other, and in fact have close relatives that cannot learn
song, he said. Despite their evolutionary distance, the new
research indicates that hummingbirds use the same seven structures
in the brain that parrots and songbirds use when they are singing
their learned vocalizations structures that aren't even present in
non- vocal learning orders of birds.
The finding raises the evolutionary question of whether the
three orders of birds developed the ability to learn song
independently, and each time developed similar brain structures to
serve this purpose. Alternately, there may have been a common
ancestor with the ability to learn song, and only a few of the
descendants retained this ability along with the specialized brain
regions.
Jarvis said that all the evidence supports the former
explanation (that vocal learning developed independently three
times) and points to another example of independent evolution the
similar development of wings from limb structures in pterosaurs
(ancient flying dinosaurs), bats and birds.
"The reason why wings evolved in a similar way is because
there is an environmental constraint, the center of gravity,
placed on how animals can fly," he explained. "Here, I think there
is an interaction between the environment and the brain, and
Mother Nature has a basic constraint, even instructions, on how
you can develop brain structures for a complex behavior such as
vocal learning."
In applying the bird findings to mammals, Jarvis pointed out
that, like the bird family, mammals have only a few members who
demonstrate learned vocalizations humans, bats, whales and
dolphins. The evolutionary implications of the bird research may
impact the study of how and why these few mammals have developed
the ability to learn speech or sing.(…)
-
Proteins In The Amygdala Reconsolidate Memory After Retrieval, Nature
An American scientist is claiming that the ice cap at the
North Pole has melted. Dr James McCarthy, an oceanographer, says
he found a mile-wide stretch of open ocean on a recent trip to the
pole on a Russian icebreaker. Some experts believe it is the first
time in more than 50 million years that the North Pole has been
covered in water rather than ice. But other scientists say
movements in polar ice regularly create gaps in the ice cap -
including at the North Pole itself.
Attention Is Fast But Volition Is, Slow, Nature
Excerpt: 'New' memories are initially labile and
sensitive to disruption before being consolidated into stable
long-term memories. Much evidence indicates that this
consolidation involves the synthesis of new proteins in neurons.
The lateral and basal nuclei of the amygdala (LBA) are believed to
be a site of memory storage in fear learning.(…). Our data
show that consolidated fear memories, when reactivated, return to
a labile state that requires de novo protein synthesis for
reconsolidation. These findings are not predicted by traditional
theories of memory consolidation.
Scientists Watch Cities Make Their Own Weather, NYTimes
How swiftly can the object of your attention be changed?
Consider two ways to deploy attention: it can be commanded from
place to place by a deliberate act of will, or it can run freely
without specific instruction. Here we use a visual search task to
show that deliberate movement of attention is significantly slower
because of an internal limit on the speed of volitional
commands.
Self-Assembled 3D Circuits, Science
Excerpt: Atlanta is so big and hot that it makes its
own weather, and scientists have the pictures to prove it. While
analyzing weather data that was collected during the 1996 Summer
Olympics, Dr. Robert Bornstein, a professor of meteorology at San
Jose State University in California, saw a pattern in the winds.
(…)
Satellite images backed him up, revealing several instances
in which thunderstorms erupted over Atlanta, seemingly out of
nowhere, and dumped rain on the city, usually at its southeast and
northeast edges. (...)
Modulation of Human Visual Cortex by Crossmodal Spatial Attention, Science
Although self-assembly normally is associated with
molecular-scale objects, the principles of recognizing shape and
forming bonds selectively can be applied to macroscopic objects
and used to assemble chips on flat substrates. Gracias et al. (p.
1170) show how electrical circuits in three dimensions can be
built up from millimeter-scale polyhedra that were patterned with
wires, light-emitting diodes, and solder dots. When placed in
solution just warm enough to melt the solder, the polyhedra
assembled into larger structures in a manner determined by the
placement of the dots and wires.
- Forming
Electrical Networks in Three Dimensions by
Self-Assembly,
David H. Gracias, Joe Tien, Tricia L. Breen, Carey
Hsu, and George M. Whitesides, Science, Vol. 289, No
5482, August 18 2000, p. 1170
A Highly Sensitive Neuronal Trigger, Science
What mechanism underlies the phenomenon in which touching
one's hand can improve vision in the nearby area? In a functional
magnetic resonance imaging study, Macaluso et al. (p.
1206;
see the Perspective by de Gelder) showed that a sudden touch
enhances activity in a brain area called the visual cortex. This
enhancement is the result of neuronal input from higher multimodal
association cortex areas back-projecting onto the visual
cortex.
The Position of Moving Objects, Science
Neurotransmitter release from vesicles in the presynaptic
terminal is triggered by a brief increase in calcium. There has
been a long debate concerning the sensitivity of the vesicular
calcium sensor for mammalian central synapses and the minimal
calcium concentration that is necessary to start the subsequent
molecular events that lead to vesicle fusion with the plasma
membrane. Bollmann et al. (p. 953)
measured laser-induced release of caged calcium in a rat auditory
brainstem synapse and found that increases in calcium
concentrations of 1 micromolar evoked release. The authors'
analysis indicates that a brief spike of 10 micromolar calcium
would be sufficient to match the rate of synaptically evoked
neurotransmitter release. This result implies that the calcium
sensor in the presynaptic terminal has a high calcium
affinity.
- A
Highly Sensitive Trigger,
This Week in Science, Vol 289, No
5481, August 11 2000
- Calcium
Sensitivity of Glutamate Release in a Calyx-Type
Terminal ,
Johann H. Bollmann, Bert Sakmann, J. Gerard G. Borst,
Science, Vol. 289, No 5481, 11 Aug 2000, pp.
953-957
Soros Concedes His Forecast on Global Economy Was Off, NYTimes
Eagleman and Sejnowski (Reports, 17 March, p. 2036),
studying the visual illusion known as the flash-lag effect, framed
a "postdictive" model in which the flash resets motion integration
in the visual system and "the percept attributed to the time of
the flash is a function of events that happen in the ~80
milliseconds after the flash." Their results, they suggested, do
not support the two previously proposed models, predictive motion
extrapolation and differential latency. (…)
There has been a dispute about that theory with new
experimental data.
- The
Position of Moving
Objects, Bart
Krekelberg, Markus Lappe, David Whitney, Patrick
Cavanagh, David M. Eagleman, and Terrence J.
Sejnowski, Science Vol. 289, No 5482, 18 Aug 2000, p.
1107
- See also: When
is "Now"?, Complexity
Digest 2000.11.1
SFI Workshop: Structure and Dynamics of Complex Interactive Networks, Comment
Excerpt: George Soros, one of the world's most
successful speculators and richest men, has come as close as
anyone to personifying the spread of global capitalism and the
power of international financial markets. So, in 1998, when he
wrote a book predicting the imminent "disintegration of the global
capitalist system," his views caused quite a stir.
Two years later, the global economy is still kicking, and,
in a new book, Mr. Soros, who turns 70 years old today, is taking
back his grave forecasts. (...)
Call for Nonlinear Geophysics Abstracts, Announcement
The Workshop was terrific in presenting a tremendous variety
of networks that share common characteristics. For the neural
network in the brain, and the electric power grid, and the social
networks, a key question to work on is "How do they form?" In each
case there are governing objectives and also constraints. The
networks design themselves -- and the discussion of robustness and
fragility is highly relevant to understanding those design
principles, which are in most cases local.
I believe that real progress will be made as a consequence
of the Workshop.
NECSI.edu -> ISCE.edu, Announcement
Fall AGU 2000, San Francisco (15-19 December 2000)
[Deadline: Sept 1 by snail mail, Sept 7 electronically]
The AGU (American
Geophysical Union) nonlinear geophysics (NG)
committee is pleased to announce,12 special sessions with NG
sponsorship, and 9 with NG co-sponsorship. These include
applications to hydrology, atmospheric sciences, ocean sciences,
seismology, tectonics, geomorphology, geodesy, geomagnetism, space
sciences, biogeosciences, prediction, and natural hazards
.
Titles of special sessions:
- NG01 Nonlinear Space-Time Patterns
- NG02 Geocomplexity: Self-Organizing Systems
- NG03 Scaling and the Extremes of Geophysical Fields
- NG04 Nonlinearity and Earthquakes
- NG05 Fractals, Chaos and Self-Organized Criticality in
Natural and Human-Induced Hazards
- NG06 Quantifying Predictability in Geophysical Systems
II
- NG07 Scaling, Multifractals and Upscaling and
Downscaling Techniques in Precipitation and Hydrology
- NG08 Scaling Laws and Non-Linear Dynamics in Drainage
Basins, Vegetation Patterns, and Geomorphic Processes
- NG09 Biocomplexity in the Environment
- NG10 Visual Computing in Nonlinear Geophysical
Phenomena
- NG11 Anomalous Transport in Inhomogeneous and (Multi-)
Fractal Geophysical Media
- NG12 Dynamical Structure and Persistence: Nonlinear
Analysis of Superposed Natural Processes With Different
Characteristic Times
