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Number 445, August 25, 1999 by Phillip F. Schewe and Ben Stein
NEW THEORY OF EPILEPSY. Epilepsy is a sort of hurricane in the brain; its onset is marked by a transition from the customary uncoordinated (perhaps even chaotic) firings of neighboring neurons into (ironically enough) a periodic common firing. A hurricane's awesome organization comes from rising tropical heat entraining surrounding air masses in a cyclonic motion. The organizing principle behind epileptic seizures, by contrast, is not yet known. At present the main way of studying seizures is with electroencephalograms (EEGs) which, useful as they are, can provide only a superficial (the electrodes sit on the scalp), averaged signal map blurred by the passage of the electrochemical currents through tissue, blood, and bone. To monitor a seizure with greater detail, one would like to fly right into the center of the storm. In recent years this has been possible with the implantation of "depth electrodes" in the "focus" region of the hippocampus (the staging point for some of the most intractable forms of epilepsy). This provides a spatial resolution of one to two orders of magnitude better than conventional electrodes. Such work is being carried out at Indiana University Purdue University at Indianapolis (contact Raima Larter, 317-274-6882, larter@chem.iupui.edu), where researchers are now presenting a new theory of epilepsy. Epilepsy is a "dynamical disease," arising not from any structural abnormality or from any chemical deficiency or surplus, but rather from the temporary excursion of a critical parameter outside of some acceptable window of behavior. Knowing what this parameter is could lead to new therapies. The IUPUI scientists suspect the mystery parameter might be the speed of communication among the synchronized neurons. And this speed, in turn, might be related to how glial cells (once thought of being no more than the "glue" between neurons) process calcium ions. Indeed, the glia are now known to be sensitive to neurotransmitters, which initiate waves of calcium concentration among the glia like water waves rolling around a swimming pool. Thus the coming and going of epilepsy might be related to a chemical wave in the brain. (Larter et al., Chaos, September 1999; copies of the article can be obtained from AIP Public Information; figures at www.aip.org/png/html/epilepsy.html.)
A LINEAR DECELERATOR FOR NEUTRAL MOLECULES, identical in principle to a linear accelerator (LINAC) for charged particles, has been demonstrated by researchers in the Netherlands (Gerard Meijer, University of Nijmegen, 011-31-24-365-2277, gerardm@sci.kun.nl), providing a new way to cool molecules to ultralow temperatures. Previous methods for cooling molecules either depend upon the presence of a cold background gas and magnetic fields (Update 393), or they are restricted to those molecules which can be formed by combining already cold trapped atoms. In their demonstration, the researchers constructed a 35-centimeter long "Stark decelerator," containing a succession of 63 pulsed electric fields. The decelerator can slow down any neutral molecule with a permanent dipole moment, i.e., a permanent separation of electric charge within the molecule. This includes any diatomic molecule composed of two different elements (such as NaCl), but also molecules like H2O and NH3. The researchers chose to demonstrate their technique with carbon monoxide (CO). When a pre-cooled mixture of CO in xenon gas entered the linear decelerator, each molecule experienced the Stark effect; at every electric field, their internal energy shifted upward and caused them to lose some kinetic energy. After passing through all 63 electric-field stages, a subset of the CO molecules was slowed down from 225 m/s to 98 m/s, with an equivalent temperature of 30 millikelvin. Additional electric field stages could in principle cool the molecules further. This technique promises to be useful for cold-molecule physics, a field which is "expected to bloom in the next decade," says Meijer. (Bethlem, Berden and Meijer, Phys. Rev. Lett., 23 August 1999.)
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