Scientists have developed a new model of how the brain tells time, which challenges the popular theory of an internal clock that generates and counts regular fixed moments.

Researchers at the University of California, Los Angeles, suggest that a series of physical changes to the brain's cells help it track the passage of time.

"If you toss a pebble into a lake, the ripples of water produced by the pebble's impact act like a signature of the pebble's entry time. The farther the ripples travel, the more time has passed," Dean Buonomano, associate professor of neurobiology and psychiatry at the David Geffen School of Medicine at UCLA, said in a prepared statement.

"We propose that a similar process takes place in the brain that allows it to track time. Every time the brain processes a sensory event, such as a sound or flash of light, it triggers a cascade of reactions between brain cells and their connections. Each reaction leaves a signature that enables the brain-cell network to encode time," said Buonomano, who is also a member of UCLA's Brain Research Institute.

Using a computer model, the researchers demonstrated that this kind of network could tell time. Their new model is outlined in an article in the Feb. 1 issue of the journal Neuron.

"The value of this research lies in understanding how the brain works. Many complex human behaviors -- from understanding speech to playing catch to performing music -- rely on the brain's ability to accurately tell time. Yet no one knows how the brain does it," Buonomano said.