Number 236, August 7, 1995 by Phillip F. Schewe and Ben Stein
A SILICON DEVICE FOR TRIGGERING ELECTRICAL ACTIVITY IN A NERVE CELL
has been constructed, opening possibilities for two-way, non-toxic communication
between computer chips and nerve cells. Previous devices for stimulating
nerve cells were metallic devices generating ordinary electric currents.
Not only do such devices have corrosion-prone electrodes, but their currents
create electrochemical byproducts and heat that could damage the nerve
cells and themselves. The silicon device, constructed by researchers at
the Max Planck Institute for Biochemistry in Germany, contains a "stimulation
spot" that triggers neural activity simply through the rearrangement
of electric charge. Insulated by silicon oxide, the stimulation spot has
a size (between 10 and 50 microns) matched to that of a leech nerve cell
to which it is connected. A voltage pulse applied to the spot rearranges
electric charge on the silicon oxide film and the insulating membrane of
the nerve cell, creating a buildup of positive charge in the nerve cell
which causes it to fire above a certain threshold. The silicon device is
capable of triggering a single nerve cell without affecting other nearby
neurons. The device complements the previously designed "neuron transistor,"
which receives ionic signals from nerve cells and transcribes them to electronic
signals in silicon. "These two devices join the two worlds of information
processing, the silicon world of the computer and the water-world of the
brain," says the Max Planck Institute's Peter Fromherz (fromherz@vms.biochem.mpg.de).
Developing this device for biomedical applications, such as computer-controlled
artificial limbs, is not envisioned at the present moment, as researchers
will first need to build and understand devices that interact with connective
tissue and other non-neuronal cells in the body. (Peter Fromherz and Alfred
Stett, 21 Aug., Physical Review Letters; text and figures are available
from AIP Public Information, 301- 209-3091, physnews@aip.org.)
GENERAL RELATIVITY HAS SURVIVED ANOTHER TEST. Einstein's theory predicts
that the light from a distant star will be slightly deflected in the gravitational
field of a large body. In 1919 Arthur Eddington observed just such a deflection
of starlight as it grazed the sun. The measurement, in agreement with the
relativity prediction, helped to make Einstein world famous. Performing
a new version of this test, astronomers from Harvard, MIT, and the Haystack
Observatory (contact Brian Corey, 508-692-4764) have used antennas in Massachusetts
and California to measure the deflection of radio waves coming from the
extragalactic object 3C279 as they passed near the sun. The use of coordinated
but widely spaced antennas (very long baseline interferometry) produces
a much more accurate measurement than is possible with a single radio telescope.
The ratio of measured to predicted deflection was 0.9998, with an uncertainty
of 0.0008. (D.E. Lebach et al., 21 Aug., 75, 1439 Physical Review Letters.)
ULYSSES IS NOW PASSING OVER THE SUN'S NORTH POLAR REGION. Launched in
1990, the Ulysses spacecraft does not take photographs but instead monitors
the magnetic fields and the fluxes of cosmic rays and solar wind particles
in the greater solar environment. Now that Ulysses has gone over the top
its main task has been fulfilled, but scientists are hoping that the mission
can be extended at least to the year 2000, when the craft would return
to the solar antipodes at a time when the sun would be in the most active
phase of its 11-year cycle. (Eos, 25 July 1995.)
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