Subthreshold muscle twitches dissociate oscillatory neural signatures of conﬂicts from errors Michael X Cohen a,b, ⁎, Simon van Gaal a,c,d,e a Department of Psychology, University of Amsterdam, The Netherlands b Department of Physiology, University of Arizona, United States c Inserm, Cognitive Neuroimaging Unit, Gif-sur-Yvette, France d Commissarìat à l'Energie Atomique, Neurospin Center, Gif-sur-Yvette, France e Radboud University Nijmegen, Donders Institute for Brain, Cognition and Behavior, The Netherlands abstract article info Article history: Accepted 21 October 2013 Available online 1 November 2013 Keywords: Medial frontal cortex Theta Partial errors Oscillations Cognitive control Errors EEG Connectivity Time-frequency We investigated the neural systems underlying conﬂict detection and error monitoring during rapid online error correction/monitoring mechanisms. We combined data from four separate cognitive tasks and 64 subjects in which EEG and EMG (muscle activity from the thumb used to respond) were recorded. In typical neuroscience experiments, behavioral responses are classiﬁed as “error” or “correct”; however, closer inspection of our data re- vealed that correct responses were often accompanied by “partial errors”— a muscle twitch of the incorrect hand (“mixed correct trials,” ~13% of the trials). We found that these muscle twitches dissociated conﬂicts from errors in time-frequency domain analyses of EEG data. In particular, both mixed-correct trials and full error trials were associated with enhanced theta-band power (4–9 Hz) compared to correct trials. However, full errors were additionally associated with power and frontal–parietal synchrony in the delta band. Single-trial robust multiple regression analyses revealed a signiﬁcant modulation of theta power as a function of partial error correction time, thus linking trial-to-trial ﬂuctuations in power to conﬂict. Furthermore, single-trial correlation analyses revealed a qualitative dissociation between conﬂict and error processing, such that mixed correct trials were associated with positive theta-RT correlations whereas full error trials were associated with negative delta-RT correlations. These ﬁndings shed new light on the local and global network mechanisms of conﬂict monitoring and error de- tection, and their relationship to online action adjustment. © 2013 Elsevier Inc. All rights reserved. Introduction Several cognitive control processes, including response conﬂict monitoring and error processing, rely on brain structures within the medial prefrontal cortex (Nachev, 2006; Ridderinkhof et al., 2004b; van Veen and Carter, 2006). Response conﬂict arises when multiple response options are activated and only one must be selected, whereas error processing occurs when an incorrect response is made. Some have argued that conﬂict and errors are processed by the same neural system (van Veen and Carter, 2006; Yeung et al., 2004), on the basis of cognitive models and similar topographical distributions of EEG during conﬂict and error trials, and spatially overlapping patterns of activation in fMRI studies (Ridderinkhof et al., 2004a). Others have argued that errors and conﬂicts are processed by different neural systems (Falkenstein et al., 2000; Swick and Turken, 2002) and may recruit somewhat disso- ciable spatial regions within the medial frontal cortex (Mathalon et al., 2003; Nee et al., 2011; Ullsperger and von Cramon, 2001). Whether errors and conﬂict lead to the same neurocognitive process can be difﬁcult to test empirically, because errors often occur when conﬂict is already present. Conﬂict, on the other hand, should be easier to isolate from errors. Typically, conﬂict effects are examined by com- paring trials in which conﬂict is induced by the experiment with trials in which conﬂict is not induced by the experiment. This occurs, for ex- ample, in the Stroop task, when the word RED is printed in blue ink. A valid interpretation of condition differences relies on the assumption that subjects experienced response conﬂict in one condition and not in the other. Although there are clear behavioral condition differences that support this assumption–reaction times (RTs) are generally longer and error rates higher in conﬂict conditions–there is also thought to be conﬂict during conditions that supposedly contain no conﬂict (Coles et al., 2001), and there are ﬂuctuations in cognitive control that affect how much conﬂict is experienced on each trial, depending on previous trial and other contextual events (Egner, 2007; Gratton et al., 1988). Thus, a more ideal way to test for conﬂict would be to measure it directly. One approach is to perform trial-to-trial brain-behavior analyses, wherein trial-varying brain activity is correlated with trial-varying RTs. However, RTs can vary across trials for a number of reasons unrelated to conﬂict, in- cluding general attention and other non-speciﬁc cognitive factors (Carp et al., 2011; Esterman et al., 2012; Weissman et al., 2006). Comparing NeuroImage 86 (2014) 503–513 ⁎ Corresponding author at: Department of Psychology, University of Amsterdam, The Netherlands. E-mail address: mikexcohen@gmail.com (M.X. Cohen). 1053-8119/$ – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.neuroimage.2013.10.033 Contents lists available at ScienceDirect NeuroImage journal homepage: www.elsevier.com/locate/ynimg