Understanding the machinery of interval timing is profoundly difficult because it is "amodal," said Buhusi and Meck. That is, the interval timing clock is independent of any sense -- touch, sight, hearing, taste or smell. Thus, it cannot be localized in a discrete brain area, as can the circadian clock, which has clear inputs from the visual system and outputs that control the cyclic release of circadian hormones.
"So, this process has to be distributed so it can integrate information from all the senses," said Meck. "But more importantly, because it's involved in learning and memory, you could argue that time isn't directly perceived, but that we make temporal discriminations relative to memories of previous durations. Such features have made the machinery of interval timing more elusive, and some even questioned whether an internal clock of this sort even exists."
In the 1980s Meck and his colleagues at Brown and Columbia Universities proposed what became the traditional theory for explaining interval timing which involved a "pacemaker-accumulator" model. This model holds that somewhere in the brain lurks an independent biological pacemaker that regularly emits neural timing pulses or "ticks." However, more recent research by Meck and his colleagues at Duke, has led to the development of a "striatal beat frequency" model of interval timing involving the "coincidence detection" of oscillatory patterns of neural activity. The striatum is a part of the brain structure known as the basal ganglia, which control basic body functions such as movement.
In this model, explained Buhusi, "each structure in the brain contributes its own resonance, and all these oscillations are monitored and integrated by the basal ganglia or striatal circuits