ERPs and PET analysis of time perception: Spatial and temporal brain mapping during visual discrimination tasks

ERPs were recorded from 12 subjects performing duration and intensity visua l discrimination tasks which have been previously used in a PET study. PET data showed that the same network was activated in both tasks [P. Maquet et al., NeuroImage 3:119-126, 1996]. Different ERP waveforms were observed fo r the late latency components depending on the dimension of the stimulus to be processed: frontal negativity (CNV) for the duration task and parieto-o ccipital positivity (P300) for the intensity task. Using BESA software, the sources were first modelled with a "PET dipolar model" (right prefrontal, right parietal, anterior cingulate, left and right fusiforms). To obtain a better fit for ERPs recorded in each task, two sources (cuneus, left prefro ntal area) had to be added. Consistently with PET findings, dipole modellin g indicates that duration and intensity dimensions of a visual stimulus are processed in the same areas. However, ERPs also reveal prominent differenc es between the time course of the dipole activations for each task, particu larly for sources contributing to the late latency ERP components. In the i ntensity task, dipoles located in the cuneus, the anterior cingulate, and t he left prefrontal area yield largest activity within the P300 interval, th en activity diminishes rapidly as the stimulus ends, whereas in the duratio n task, the cuneus and anterior cingulate are still active several hundred milliseconds following stimulus offset. Moreover, in the duration task, the activity of the right frontal dipole parallels the CNV waveform, whereas i n the intensity task, this dipole is largely inactive. We assume that the r ight frontal area plays a specific role in the formation of temporal judgme nts. (C) 2000 Wiley-Liss, Inc.