How Does the Brain Count the Time?

All the events in our lives happen as if they had been scheduled by a clock.

For long, researchers have assumed that the brain has an inner clock that keeps track of time and schedules the body's activity.

A recent UCLA study comes with a novel model trying to explain the physical changes tht happen in neurons that enable the brain to monitor the passing of time. "The value of this research lies in understanding how the brain works," said Dean Buonomano, associate professor of neurobiology and psychiatry at the David Geffen School of Medicine at UCLA and a member of the university's Brain Research Institute. "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."

The most accepted hypothesis says that the brain monitors the time with a clock-like mechanism, which generates and counts regular fixed impulses. But Buonomano's rejects the existence of a clock. "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. We propose that a similar process takes place in the brain that allows it to track time," he explained. "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."

The team used a computer simulation of a network of interconnected neurons in which each connection shifted over time in response to stimuli. The model enabled the researchers to reveal that the network could tell the time: a specific event is encoded within the context of events that precede it. If one could measure the response of many neurons in the brain to a tone or a flash of light, the response would reveal both the nature of one particular event, of previous events and when they happened.

The subjects in the study were asked to assess the interval between two auditory tones under a variety of different conditions. Their timing sense was affected when the interval was randomly preceded by a "distracter" tone. "Our results suggest that the timing mechanisms that underlie our ability to recognize speech and enjoy music are distributed throughout the brain, and do not resemble the conventional clocks we wear on our wrists," said Buonomano.

"Because time-related information is critical to understanding speech, determining how the brain tells time represents an important step toward understanding the causes of diseases, such as dyslexia, that result in impaired linguistic abilities," he noted.

Future investigations will assess how a large number of neurons react to verify if they encode clues about the timing of stimuli.