Study I revealed diminished dERN amplitudes in a probabilistic learning task as a function of higher OC symptomatology, with no differences in avoidance learning. These findings were replicated in a second independent sample, which also replicated the increasingly robust findings from the literature of larger dERN amplitudes in simple motor response tasks as a function of higher OC symptoms (
Endrass et al., 2008;
Gehring et al., 2000;
Hajcak et al., 2008;
Hajcak & Simons, 2002;
Johannes et al., 2001;
Ruchsow et al., 2005;
Santesso et al., 2006). This finding of a task-related dissociation in dERN amplitude as a function of obsessive-compulsive symptoms indicates that different, yet partially overlapping neural mechanisms may underlie the ERN following the execution of an erroneous motor response and following suboptimal choices in a probabilistic learning paradigm. Differential modulation of medial prefrontal systems may be related to obsessive-compulsive symptoms, with hypoactivity in systems promoting active avoidance, but hyperactivity in systems that perpetuate a previously maladaptive response. The former process may contribute to the inability to learn to avoid making repetitive behaviors that continually produce error signals (which would otherwise serve to extinguish such behaviors), and the latter may further exacerbate this situation by causing repeated attempts to ‘perfect’ behaviors that did not produce the desired outcome.
The lack of behavioral differences in the tasks reported here suggests that the OC-dependant modulation of underlying neural systems may not reflect hyperactive action monitoring tendencies, and also that the differential activation of these systems in OCD may not directly lead to alterations in behavior on these tasks, a finding generally consistent with the extant literature on OC populations and error monitoring (
Endrass et al., 2008;
Fitzgerald et al., 2005;
Gehring et al., 2000;
Hajcak & Simons, 2002;
Johannes et al., 2001;
Maltby et al., 2005; Nieuwenhuis et al., 2005;
Ruchsow et al., 2005;
Santesso et al., 2006;
Ursu et al., 2003). A predicted correlation between ERN amplitude and avoidance (NoGo) learning was supported in this investigation (
Frank et al., 2007;
Frank et al., 2005a), although this correlation was non-significant with dERN amplitude. While there were slight variations in the predictive power of ERN or dERN amplitudes, combined data from Study I and Study II indicate that larger ERN amplitudes correlated positively with NoGo learning and negatively with OCI-R score, yet OCI-R score did not relate to NoGo learning.
A previous report detailed a null-result regarding ERN and FRN differences between OCD patients and a control group utilizing a probabilistic learning task (
Nieuwenhuis et al., 2005a). In fact, this investigation found a non-significant negative correlation between OCD and ERN amplitude, a previous anomaly in the literature of OC populations and the ERN, but one that is in line with the findings presented here. The authors of this study speculated that trial-to-trial feedback reduces action monitoring demands in OCD, and that the response-monitoring system in OCD may only become hyperactive once stimulus-response mappings are known. These two processes, trial-to-trial feedback and undetermined stimulus-response mappings, are hallmarks of reinforcement learning. We suggest a broader perspective: that there are fundamental differences in the neural systems underlying suboptimal choices during reinforcement learning and motor errors of commission, and that OC symptoms reflect dissociation in the functioning of these systems.
A number of studies have examined hyperactive error signals as an electrophysiological correlate of performance monitoring in psychiatric populations (for a review see:
Ullsperger, 2006 as well as
Olvet & Hajcak 2008). Depression, pathological worry, trait anxiety and negative affect have been characterized by increased error-related signal amplitudes (Hajcak, McDonald, Simons, 2004;
Chiu & Deldin, 2007;
Hajcak, McDonald, & Simons, 2003;
Luu, Collins, & Tucker, 2000;
Tucker, Luu, Frishkoff, Quiring, & Poulsen, 2003,
Paulus, Feinstein, Simmons & Stein, 2004), but see
Ruchsow et al. (2006;
2004). Arguably, all internalizing psychiatric disorders mentioned above may be characterized by increased sensitivity to errors, whereas externalizing aspects of psychiatric disorders (e.g. impulsivity, substance abuse) are associated with decreased error related activity (
Ridderinkhof et al., 2002;
Franken, van Strien, Franzek, & van de Wetering, 2007;
Easdon et al., 2005). However, there has never been a theory of why ERN amplitudes should be differently modulated by task demands as a function of psychopathological traits. This phenomenon offers a simple methodological advancement that may be applied to future investigations of how medial prefrontal systems are differentially affected by aspects of psychopathology.
Comorbidity between OCD and depression is reported to be high, with as many as one-half of OCD patients suffering from Major Depressive Disorder (
Abramowitz, Storch, Keeley, & Cordell, 2007;
Hong et al., 2004;
Nestadt et al., 2001). Only Study I demonstrated a correlation between OCI-R and BDI and between BDI and dERN amplitude. However, given that neither of these correlations were obtained in the second sample with either the probabilistic learning paradigm or the flanker task, it seems more parsimonious to conclude that these ERN alterations are more likely to be related to OC symptomatology than comorbid depressive symptomatology in this investigation. The use of student populations for clinical analogues demands replication with OCD patients, but this methodology provides unique advantages: the psycho-pharmaceutical naivety of the studied group, homogeneity in age, and the ease of using larger sample sizes. Moreover, because a diagnostic interview was not administered, it may well be the case that some of the participants in the present studies in fact meet OCD diagnostic criteria, which would not be surprising given the early age of onset (
Lensi et al., 1996;
Rasmussen & Eisen, 1992;
Swedo et al., 1989) and reasonably prevalent nature of OCD (
Leon et al., 1995;
Rasmussen & Eisen, 1992;
Regier et al., 1993). Future investigations with both patient and symptomatic non-patient populations will help determine whether the observed pattern of findings replicates in more severe patient groups. If so, this present approach will be useful for identifying alterations in neural systems responsible for cognitive control and reinforcement learning.
Different neural systems have been implicated in the generation of the ERN. Outcomes that are worse than expected are characterized in the midbrain by a phasic decrease in dopaminergic tone (
Hollerman & Schultz, 1998;
Schultz, 2007). The reinforcement learning theory of the ERN posits that these dips in tonic dopaminergic tone cause a disinhibition of dorsal ACC neurons, generating medio-frontal negativities (
Holroyd & Coles, 2002), although the reverse pattern of causation has also been suggested (
Frank et al., 2005a;
Pizzagalli et al., 2008). The ACC is futhermore implicated in the conflict model theory of the ERN, which posits that the degree of motor response interference causes response-related activation in the ACC (
Carter et al., 1998;
Yeung, Cohen, & Botvinick, 2004). However, neither of these theories predicts a situation where ERN amplitude should be dissociated in an interaction between task and individual differences, especially in the absence of behavioral effects.
Enhanced ERN amplitudes in OCD patients have been interpreted as in line with the neurobiological mismatch theory of OCD, whereby hyperactive error signals are trapped in a dysfunctional comparator which detects a mismatch between actual and intended response (
Gehring et al., 2000;
Pitman, 1987). However, recent findings suggest that a putative performance-monitoring dysfunction is not selective to error processing, since altered correct-response negativities are also observed (
Endrass et al., 2008;
Hajcak & Simons, 2002). In this investigation, the Feedback Related Negativity was either the same size (Study I) or smaller (Study II) than non-symptomatic controls, which also suggests that there are pervasive effects of OCD on ACC activity. It is apparent that the theoretical accounts of the ERN cannot fully explain the pattern of results from this study, although it is clear that individual difference investigations can offer evidence for future theoretical advancement of the neural systems underlying the ERN. Although there was no difference in the percentage of self-corrected trials between the groups, a possible difference in Flanker dERN amplitudes between OCI-R groups could have been due to self-corrected vs. uncorrected errors (
Gehring et al., 1993;
Ullsperger & von Cramon, 2006), but this possibility could not be investigated here due to inadequate trial counts. Since the ACC plays a necessary role in the immediate self-correction of an error (
Modirrousta & Fellows, 2008), this specific dynamic of error processing remains an intriguing variable for future investigations to parse the specificity of performance monitoring in psychiatric populations.
Evidence from the fMRI literature has shown that error and conflict-related hemodynamic responses in OCD patients are different between rostral and caudal areas (
Fitzgerald et al., 2005;
Maltby et al., 2005;
Ursu et al., 2003). The rostral part of the ACC has been related to assessing the salience of emotional and motivational information, and often shows a trade-off in activation with more dorsal areas (
Bush et al., 1998). The reciprocal activation of rostral and dorsal ACC, possibly differentially altered by OCD, might explain this dissociation in medio-frontal response related ERPs. Both rostral and dorsal areas of the ACC have been implicated in the generation of the ERN and FRN (
Gehring & Willoughby, 2002;
Holroyd, Larsen, & Cohen, 2004;
Miltner, Braun, & Coles, 1997; Nieuwenhuis, Slagter, von Geusau, Heslenfeld, & Holroyd, 2005;
Ullsperger & von Cramon, 2003), perhaps due to partial phase resetting and amplitude enhancement of the frontal midline theta (
Luu, Tucker, Derryberry, Reed, & Poulsen, 2003;
Luu, Tucker, & Makeig, 2004;
Trujillo & Allen, 2007;
Cavanagh, Cohen & Allen, 2009). Given that conflict activation has been localized more dorsally and error monitoring more ventrally in medial prefrontal cortex, (
Luu et al., 2003;
Luu et al., 2004;
Ullsperger & von Cramon, 2001), it is possible that differential activation of these separate yet partially overlapping neural systems may underlie task-specific ERN alterations as a function of OC symptomatology.
The finding that OC symptomatology was characterized by a smaller dERN in a reinforcement learning task and a larger dERN in an error commission task provides a novel foundation for future research on the role of the ACC in health and disease. OC-related alteration of the ERN may not simply be reflective of altered brain dynamics related to a ‘hyperactive action monitoring system’. Differential modulation of medial prefrontal systems may be related to obsessive-compulsive symptoms: with hypoactivity in systems promoting active avoidance, but hyperactivity in systems that perpetuate a previously maladaptive response. It is likely that there are not general behavioral impairments in action monitoring in OCD, but that OCD may be specifically characterized by a dysfunction in learning to stop making repetitive actions that produce bad outcomes. For example, it is assumed that probabilistic reversal learning is compromised in OCD patients (
Kim et al., 2003;
Remijnse et al., 2006;
Chamberlain et al., 2008;
Valerius et al., 2008), fitting with a diminished ability to avoid repetitive mistakes. Future EEG studies of OCD should investigate the role of the ERN in tasks that require avoidance of repetitive mistakes, and the possibility of differential functioning of separate, yet overlapping medial prefrontal systems involved in action monitoring.