[Time perception in functional brain imaging]

Knowledge of physiological mechanisms underlying time perception is still rather limited. The aim of our study was to search for a 'time accumulator', i.e. the part of the brain where information on the duration of time is stored.

Nine healthy volunteers were given a time reproduction task during event-related fMRI. Subjects were instructed to retain the duration of the stimulus presented (presentation phase) and then to reproduce it by pressing a button (reproduction phase). Two different analyses were made: event-related (P < 0.05, FWR corrected) and parametric (BOLD signal increase/decrease during the presentation/reproduction phases correlated with the time intervals; P < 0.01, FDR corrected). When the event-related approach was employed, activation was noted bilaterally in the inferior prefrontal cortex (IPFC), supplementary motor area (SMA), precuneus and secondary visual cortex. On the right, there was activation in the dorsolateral prefrontal cortex (DLPFC), gyrus cinguli and inferior parietal lobule. On the left, the primary sensory-motor cortex was activated. While during the presentation phase the left DLPFC activity inversely correlated with the presented duration, a nearly identical area showed positive correlation in the reproduction phase.

The event-related analysis did not allow distinguishing the process of time perception from many cognitive processes running simultaneously. In turn, the parametric analysis was based on visualizing regions, in which the signal correlated with the varying duration of the time interval provided the level of attention, decision-making and the processes of behavioral response planning and execution were constant. Moreover, the right and left DLPFC seem to play different roles in time perception. While the left one is functioning as a "time accumulator", the right one is rather involved in the recognition of previously perceived intervals.