engleski

Neural substrate of target detection in an MEG oddball study with faces

The detection of a rare target stimulus among frequent standard stimuli usually elicits the electric P300 component and its magnetic counterpart. The aim of this study was to identify the neural pathway of the target-related response in an oddball paradigm with faces in the time window 150-420 ms (including face-characteristic M170 response and P300). Eight young male subjects with MRI scans participated in the study. Grayscale faces were presented centrally for a duration of 150 ms with an inter-stimulus interval of 450 ms. Target face with glasses was presented among standard and non-target deviant faces. Measurements were carried out at the BioMag Laboratory using a 306-channel whole-head magnetometer (Elekta Neuromag Ltd., Helsinki). MEG data were analyzed assuming multiple dipoles in a sphere model and using the Cortical Start Spatio-Temporal (CSST) multi-start inverse procedure incorporated in the MRIVIEW software. Sources identified around 170 ms did not considerably differ for standards and targets except that target stimuli evoked additional frontal activity in four subjects. However, in the later time interval of 200-320 ms a strong target-related activity was evident and frontal activation was localized for all subjects despite rather large intersubject differences in cortical activations in other regions. The activity in the anterior regions was followed by the activation in the parietal cortex during the time window of 320-420 ms. The identified cortical pathway was selectively activated by the attentional switch to the target and consequently might represent a neural correlate of target detection.

MEG; face processing; oddball paradigm

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