Carving the clock at its component joints: neural bases for interval timing

Area of Science:

• Cognitive Neuroscience
• Neuroimaging
• Psychology

Background:

• Time perception models commonly propose an 'internal clock' mechanism.
• This internal clock is theorized to comprise at least two key components: an accumulator and a comparator.
• The precise neural underpinnings of these distinct temporal processing components remain incompletely understood.

Purpose of the Study:

• To investigate the hypothesis that separate distributed neural networks underlie the accumulator and comparator functions of time perception.
• To identify brain regions associated with processing stimulus duration (accumulator) and task difficulty (comparator) during a temporal discrimination task.

Main Methods:

• Functional magnetic resonance imaging (fMRI) was employed to monitor brain activity.
• Participants performed a temporal discrimination task involving two visual stimuli (S1 and S2) of varying durations.
• Regions of interest were defined anatomically to analyze neural correlates of S1 duration and comparison difficulty.

Main Results:

• Neural activity correlating with the duration of the first stimulus (S1) was observed in the left inferior frontal gyrus, supplementary motor area (SMA), and superior temporal regions.
• Brain activity associated with the difficulty of the temporal comparison task significantly correlated with activity in bilateral inferior frontal gyri.
• These findings suggest distinct, yet partially overlapping, neural substrates for accumulator and comparator functions.

Conclusions:

• The accumulator component of the internal clock, related to tracking stimulus duration, is mediated by a network including left inferior frontal, SMA, and superior temporal regions.
• The comparator component, involved in judging temporal differences and influenced by task difficulty, is associated with bilateral inferior frontal gyri.
• Distinct neural networks, with some overlap, support the functional components of the internal clock model of time perception.