Magnetic chorus plunges into chaos.

Heart rhythms, the interplay of oscillating electrical signals, and even the drifting of a leaf may fall into so-called chaotic patterns that appear random but follow strict rules. Because a slight change at the start of a chaotic process can lead to a radically different outcome, the specific course of chaotic events defies prediction (SN: 1/25/97, p. 52; 10/31/98, p. 285).

Now, to their surprise, researchers have found that radio signals elicited from molecules by magnetic field pulses can also turn chaotic. Magnetic resonance imaging (MRI) machines and related scientific devices rely on those signals to characterize both tissues and nonliving materials.

Yung-Ya Lin, Warren S. Warren, and their colleagues at Princeton University stumbled upon the unpredictable behavior during experiments with a nuclear magnetic resonance (NMR) spectrometer, an instrument commonly used for determining the configurations of molecules. Warren says that the chaotic patterns, which the scientists reported in the Oct. 6, 2000 SCIENCE, probably arose because of subtle magnetic interactions between molecules. The role of those interactions in magnetic resonance signals was not recognized until the Princeton team focused on them in the early 1990s (See main story).

The newly unveiled chaos has probably been at the root of some widely noticed, puzzling anomalies in NMR studies of biomolecular structures, the Princeton researchers speculate. Now scientists are beefing up NMR devices to serve as more powerful molecular microscopes for the next step in analyzing proteins identified by the huge human-genome-sequencing projects. As they continue, problems related to chaos could increase, NMR researchers say. The new findings are "a very useful warning that very nasty things may happen," says Jean L. Jeener of the Free University of Brussels in Belgium.

Although Jeener rightfully worries that chaotic behavior may amplify the unwanted signals in NMR experiments, swamping the meaningful signals, the presence of chaos could also prove to be a benefit, Warren notes. Researchers who learn to control the chaotic amplification of tiny fluctuations in the magnetic environment may find themselves able to sense extremely small magnetic variations in biological tissues and other samples. That enhanced sensitivity might raise NMR techniques to new and even more useful heights.

P.W.