Error related fields: localizing the magnetic equivalent of the ERN

Abstract

Introduction:Research in the field of error processing and error related brain activity has a long history in the field of neuropsychology. It has been found in numerous EEG studies, that a typical brain potential arises following an erroneous response. This error related negativity (ERN) and the accompanying positivity (Pe) are thought to be related to error monitoring and feedback. This is crucial for the detection of errors and correction of actions in the framework of organization of complex behaviors and high-level goals. Yet so far, only a single published study investigated the magnetoencephalographic equivalent to the ERN (mERN) by means of single dipole modeling. This study as well as previous EEG works suggests the major source of the ERN to be located in the anterior cingulate cortex (ACC).Here, we implemented a computerized version of the paper-and-pencil d2-test, to measure the error related field in the MEG and to localize the generator of the ERN using a distributed source model.Methods:13 (5 male/ 8 female) student volunteers participated in this study. We measured the MEG during a 15-minute stimulation period with a 148-channel magnetometer system (MAGNES 2500 WH, 4D Neuroimaging, San Diego, USA). The stimulation consisted of the presentation of the d2-test stimuli and the participants had to indicate via button press whether the stimulus was a d accompanied by two marks or not. Correct and incorrect button presses were recorded. 4 Second snippets around the triggers were extracted and analyzed. Raw data was 1 Hz high pass filtered and trials containing artifacts were excluded from analysis. Trial number in the two conditions was equalized, in order to assure equal signal-to-noise ratio.After averaging the single trials, a nonparametric permutation test was used to identify clusters of activation in time and sensor space. Subsequently, time-windows of significant effects found in the ERF analysis were modeled in source space using a linearly constrained minimum variance (lcmv) beamformer. Statistical differences on the source level were confirmed using a dependent samples t-test. All analysis steps were performed using Fieldtrip (http://www.ru.nl/neuroimaging/fieldtrip/).Results:Cluster analysis revealed a parietal cluster of activation between 80-160 ms after motor response, where the incorrect responses elicited significantly larger field amplitude than the correct responses (p