Parsing the temporal evolution of brain activity in duration discrimination
with electro- and magneto-encephalography

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

Laboratoire de Neurosciences Cognitive & Imagerie Cérébrale, CNRS UPR640-LENA, Hôpital de la Salpêtrière, Paris, France

In the study of the cognitive processes involved in time perception, duration comparison tasks have been repeatedly used. Performance in such tasks require subjects to encode a target duration and, after a delay period, to compare it with a test duration. Contrasting with the extensive body of behavioural results, little knowledge has been gathered regarding both the neural bases and the time course of the operations they subserve. In the present study, we methodically investigated these two aspects by varying task parameters as EEG or simultaneous EEG-MEG were recorded in young healthy participants. In a first experiment focussing on role of the memorized target duration, subjects were block-wisely given fixed target intervals of two different lengths (600ms or 800ms, marked by 20ms tones), while random test durations were presented. In a second experiment, a two-interval force choice task based on duration was contrasted with an analogous frequency discrimination task employing the exact same set of stimuli. Preliminary results from distributed source reconstruction of the evoked electric and electromagnetic activity show a distributed network of cortical regions encompassing superior temporal, lateral and medial prefrontal as well as parietal cortices. Time courses of regional activity reveal distinct roles for these latter at successive stages of the timing task supporting the role of medial prefrontal cortex in encoding and maintenance while lateral prefrontal regions would be involved in maintenance and comparison operations. Comparison with the frequency discrimination indicates partly overlapping activities involved in common task-unspecific processes.