Time courses and topographies of MEG and EEG signals evoked by visual and auditory duration perception

Karim N'Diaye, Richard Ragot, Line Garnero, Viviane Pouthas

Cognitive Neuroscience & Brain Imaging Laboratory, CNRS UPR640-LENA, Hôpital de la Salpêtrière, Paris, France

Time perception refers to the coding and the manipulation of temporal information, especially when short time intervals (~1 sec) are concerned. Until now, little is known on the neural substrates of human timing ability, especially regarding the role of sensory modality. We addressed this issue by analyzing simultaneous scalp electric (EEG) and magnetic (MEG) recordings of 13 young male participants involved in a "temporal generalization" task: Subjects were asked to discriminate a previously memorized "standard" duration (700ms) from randomly presented test-stimuli (ranging from 490 to 910ms). Stimuli were either auditory (a continuous 440Hz tone) or visual (a LED light) filled intervals. MEG and EEG recordings showed parallel time courses during the duration discrimination but their topographies differed: while the electric signal was mainly frontocentral, the magnetic signal peaked on temporal, temporo-parietal and parieto-occipital sensors. By computing the normalized amplitude difference maps between sustained and transient activity, we showed that duration perception was correlative with enhancements of the fronto-central negativity and of the parietal evoked magnetic field independently of the sensory modality. Source reconstruction demonstrated that these sustained potentials/fields were generated by superimposed contributions from visual and auditory cortices and from prefrontal and parietal regions. Scalp activity evoked by duration discrimination of filled intervals thus proceeds from sustained activities concurrently reflecting modality-dependent sensory processing of the on-going stimulation and supramodal cognitive processes possibly involved in timing per se.