Brain Synchronization Can Give You A Headache

By Ernie Tretkoff

The Scream (1893) by Edvard Munch (National Gallery, Oslo Norway)

Researchers studying the rhythms of electrical signals in the brain presented intriguing results at the APS March Meeting, including evidence that migraines may be related to a hyper-synchronization of brain waves, and a new technique for analyzing the brain's response to stimuli.

Physicist Sebastiano Stramaglia of the University of Bari and colleagues in Italy and at Harvard Medical School investigated how brains of migraine sufferers differ from those of healthy subjects in their response to flashes of light that simulate conditions known to trigger migraines in some patients.

An estimated 5% of Americans suffer from at least 18 days of migraine headaches a year, leading to a huge medical and financial burden. Several factors, including emotional stress, physical exertion, changes in weather, and flickering lights, are known to trigger migraines in sufferers, but no experimental model fully explains the migraine process.

Using electroencephalograms (EEG) to measure the electrical activity of the brain in 15 migraine patients and 15 controls, the researchers examined how closely signals in different regions of the brain were synchronized with each other. The researchers measured EEGs in what is known as the alpha band, 8 -12.5 hertz, which corresponds to a quiet wakeful state.

When the migraine patients were subjected to flashing light stimuli, different areas of the brain synchronized their signals more closely with each other. In control subjects, the opposite occurred—different areas of the brain decreased their synchronization with each other in response to the flashing lights.

These synchronization patterns suggest that migraines may be related to an overactive regulatory mechanism that makes patients more sensitive to environmental factors, said Stramaglia.

Though the phenomenon is not yet completely understood, Stramaglia thinks the alpha-band hyper-synchronization in migraine patients probably originates in the thalamus, a part of the brain that receives visual and auditory sensory information, then organizes and routes the information to other areas of the brain.

In another report, Peter Tass of the Institute of Medicine, Research Center, Juelich, Germany called into question the standard technique for analyzing the brain's response to stimuli and proposed a new method of analysis.

Tass seeks to understand how different areas of the brain react to pulsating stimuli and how different regions of the brain interact with each other. This information is important for the optimization of deep brain stimulation and for the study of sensory information processing.

The standard method for analyzing the brain's response to various stimuli involves averaging over a large number of trials to cancel out any background noise and extract the "real" response.

But this averaging technique, which is used in the majority of neuroimaging studies, actually cancels out a meaningful signal, leading to misleading and incorrect results, said Tass. Tass has therefore developed a more complex new analysis method, which he calls "stochastic phase resetting tomography."

In theoretical studies of a generic model of two oscillators and magnetoimaging experiments on 20 healthy subjects, Tass used his method of analysis to show that the brain's response to a stimulus is more complex than the simple resetting of the brain's rhythm that other groups have found.

Tass found that the brain often switches between qualitatively different responses across trials, a feature that the averaging analysis method fails to detect. Also, in contrast with the standard analysis, Tass said his technique provides reliable estimates of transmission times of signals between different areas of the brain.

These results could be relevant for both basic science and clinical diagnosis, said Tass. For instance, Tass's method could more reliably pick up the delay in transmission of brain signals caused by multiple sclerosis.