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Open Access Open Badges Research article

Functional definition of the N450 event-related brain potential marker of conflict processing: a numerical stroop study

Dénes Szűcs* and Fruzsina Soltész

Author affiliations

Department of Experimental Psychology, Centre for Neuroscience, University of Cambridge, Cambridge CB2 3EU, UK

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Citation and License

BMC Neuroscience 2012, 13:35  doi:10.1186/1471-2202-13-35

Published: 27 March 2012



Several conflict processing studies aimed to dissociate neuroimaging phenomena related to stimulus and response conflict processing. However, previous studies typically did not include a paradigm-independent measure of either stimulus or response conflict. Here we have combined electro-myography (EMG) with event-related brain potentials (ERPs) in order to determine whether a particularly robust marker of conflict processing, the N450 ERP effect usually related to the activity of the Anterior Cingulate Cortex (ACC), is related to stimulus- or to response-conflict processing. EMG provided paradigm-independent measure of response conflict. In a numerical Stroop paradigm participants compared pairs of digits and pressed a button on the side where they saw the larger digit. 50% of digit-pairs were preceded by an effective cue which provided accurate information about the required response. 50% of trials were preceded by a neutral cue which did not communicate the side of response.


EMG showed that response conflict was significantly larger in neutrally than in effectively cued trials. The N450 was similar when response conflict was high and when it was low.


We conclude that the N450 is related to stimulus or abstract, rather than to response conflict detection/resolution. Findings may enable timing ACC conflict effects.

Conflict processing; Interference; Subthreshold response activation; Stroop effect; Anterior cingulate cortex; Numerical distance effect; Numerical cognition; ERP; EEG