( scalp (electroencelphalograms or EEGs...)Slow brain waves play key role in coordinating complex activity

scalp (electroencelphalograms, or EEGs), brain waves are classified from the very slowest delta waves (1-3 oscillations per second) seen in very deep sleep, through theta (4-7 oscillations per second), alpha (8-13 oscillations per second) and beta (14-30 oscillations per second) to the most rapid firings in the human brain - gamma oscillations (30-60 oscillations per second). Because slow firings are detected when the brain is least active, while rapid firings accompany activity, neuroscientists think that information in the brain is carried by the high frequencies.

Until recently, scalp recordings could detect gamma waves only up to 70 firings per second, but in 1998 researchers at Johns Hopkins University discovered brain waves up to 100 oscillations per second by placing electrodes directly on the surface of the brain. Knight and his UC Berkeley group used the same technique to show last year that brain oscillations can occur up to 200 times per second - and perhaps as fast as 300 times per second. Waves with 80-200 oscillations per second are called high-gamma, though they likely play an entirely different role from the traditional lower frequency gamma waves, Knight said.

One theory is that brain oscillations organize neurons into cooperating groups: low-frequency waves synchronize the firing of large groups of neurons, while the higher frequencies synchronize smaller groups. Though neuroscientists don't know what underlying neural activity generates the waves recorded on the surface of the cortex, the oscillations may be generated spontaneously by neurons when grouped together in the hundreds of thousands.

"When you have to remember a new phone number or attend to moving cars as you cross an intersection, you'll have an increase in the strength of the theta rhythm in many different brain regions," Canolty said. "The idea is that this theta rhythm might be more of an executive control mechanism to tie different brain areas together, whe
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Source:University of California - Berkeley

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