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Unlike computers, cells in the brain use digital and analog signals at the same time to communicate with each other, researchers have found.

The finding contradicts the belief that nerve cells in the brain communicate with each other using digital code only.

In an analog system, signals can vary continuously, while digital systems represent signals by a series of pulses. The brain uses a mixture of the two to transmit signals among cells, researchers say.

David McCormick, a professor of neurology at the Yale School of Medicine, was senior author of the study, which appears in the online edition of Thursday's issue of the journal Nature.

"It's as if everyone thought communication in the brain was like a telegraph, but actually it turned out to be more similar to a telephone," McCormick said in a statement.

The research involves the axon, the wire-like portion of the nerve cell that transmits signals to adjacent cells.

Within a nerve cell, the release of neurotransmitters causes the cell's voltage to vary continuously. If the voltage reaches a certain level, an electrical discharge, called an action potential, is generated.

The action potential can travel along the axon and transmit a signal to a neighbouring cell.

Because the axon is so long and thin, scientists believed that the small fluctuations in voltage within the cell wouldn't be transmitted down the axon to another cell. They thought that only the frequency and timing of the action potentials, which is digital information, could be transmitted.

McCormick's group found that the small fluctuations in voltage in the cell can actually amplify the signal that the action potential transmits to the next cell.

For example, in the human brain, epileptic seizures and migraines both involve large changes in the voltage inside nerve cells. McCormick said the study shows that these abnormal patterns of electrical activity can be communicated from one cell to the next even if no action potentials, and no digital signals, are generated.