The brain's mysterious internal time-keeper may be a series of changes in a network of interconnected neurons, according to a U.S. researcher who discounts the idea of a ticking biological 'watch'.

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SYDNEY: The brain's mysterious internal time-keeper may be a series of changes in a network of interconnected neurons, rather than a ticking biological 'watch'.

For decades, scientists have believed that the brain possesses an internal clock that allows it to keep track of time. But publishing in the journal Neuron, researchers from the University of California at Los Angles (UCLA) proposed a new model, in which the ticking 'clock' is replaced by a series of physical changes to the neurons of the brain that enable the organ to keep track of time.

"The value of this research lies in understanding how the brain works," said study co-author Dean Buonomano of the David Geffen School of Medicine, at UCLA. "Many complex human behaviours, 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 explained that time-related information is critical to understanding speech, and believes determining how the brain tells time represents an important step toward understanding the causes of diseases such as dyslexia, which inverts word order and results in impaired linguistic abilities.

One long-held theory suggests that a mechanism in the brain generates and counts regular fixed movements, much like the way a digital watch counts the vibrations of a quartz crystal.

In contrast, Buonomano described his novel model of the brain's timekeeping device in the following way: "If you toss a pebble into a lake," he explained, "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.

"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."

To test their theory, the team created a computer-simulated network of interconnected neurons in which each connection changed gradually in response to stimuli, and showed that the network was able to keep track of time.

The group's computer simulations indicated that if they could measure the response of many neurons to a sound or a flash of light, the response would reveal not only the nature of the event but other events that preceded it and when they occurred.

Buonomano's group tested the model by asking volunteers to judge the interval between two auditory tones under a variety of different conditions. The researchers found that volunteers' sense of timing was impaired when the interval was randomly preceded by a 'distracter' tone.

Buonomano stated, "Our results suggest that the timing mechanisms that underlie our ability to recognise speech and enjoy music are distributed throughout the brain and do not resemble the conventional clocks we wear on our wrists."

According to Buonomano, the next step will to confirm the research by recording the responses to stimuli from a large number of active neurons to determine whether they encode timing information.