Seizure prelude found by chaos calculation

Concertgoers take delight in hearing the cacophony of tuning transform into the harmony of a symphony. In the brain, however, the subtle shift from a disorderly chatter of neurons into a more synchronized pattern can be a step toward the uncontrolled electrical storm of a seizure.

 Epilepsy researchers have long suspected that too much synchrony among too many neurons may be dangerous. Now, a German research team has demonstrated that a "loss of complexity" due to coordinated nerve firing is detectable in brain waves an average of 11 minutes before the onset of a seizure.

 In reaching this finding, University of Bonn researchers Klaus Lehnertz and Christian E. Elger made innovative use of a mathematical property from chaos theory, known as dimension, that many scientists had deemed useless for highly complicated biological systems such as the brain.

 The finding opens a possible way to preempt seizures, the researchers state in a report slated to appear in the June 1 Physical Review Letters.

 They are already testing whether patients whose seizures originate in the hippocampus, a region associated with memory and learning, can avoid the paroxysm by means of mere remembrances or learning tasks, Lehnertz says. The team also expects to develop in the next 3 to 4 years an implantable monitor capable of providing a warning or automatically delivering drugs or electrical stimulation.

"It's a good, solid piece of work," says Steven Schiff, a neurosurgeon and epilepsy researcher at Children's Research Institute in Washington, D.C. "In the future, if we're going to develop technologies to have electrical control of seizures, we'll need techniques like this."

 On the other hand, he says, many hurdles lie in the path of stopping seizures electrically, not the least of which is safely putting electrodes on or in the region where seizures originate, called the focus.

 Lehnertz and Elger analyzed electroencephalograms, or EEGs, from 16 awake patients whose epilepsy could not be controlled with drugs. One set of measurements covered periods just before seizures, and the other looked at periods at least 24 hours before or after seizures.

 Using an array of 30 parallel-linked personal computers to calculate dimension throughout each of their 68 observation periods, Lehnertz and Elger found that its numerical value tended to take markedly deep, long dips just before a seizure. Also, this pattern was more pronounced in tissues near the focus.

 By using dimension to assess EEGs, the researchers have revived a practice -- using chaos theory to study the brain -- that had lost credence with many researchers.

"My eyes glazed over," says Daniel T. Kaplan, a specialist in nonlinear analysis at Macalester College in Saint Paul, Minn., when he first heard of the EEG analysis. In this case, though, "it really seems to work."

 The epilepsy researchers took pains to avoid the pitfalls of earlier research by making no claim that their dimension data represent some functional characteristic of the brain's wiring.

"We don't say the brain is linear or nonlinear or chaotic or whatever. We just compare different states and nothing else," Lehnertz says.