The effect of ADHD symptoms on performance monitoring in a non-clinical population
Introduction
Many studies have shown that patients with Attention Deficit Hyperactivity Disorder (ADHD) have deficits in executive functions (for a review, see Willcutt et al., 2005) with the strongest and most consistent effects having been obtained from measures of response inhibition, vigilance, working memory, and planning. All of these tasks assess the correct and incorrect performance of cognitive processes, but ignore post-error processes. These post-error processes seem to be most relevant for task performance, as noticing and evaluating one's own error response enables us to correct the response and to improve our performance on subsequent trials. On the behavioural level, one can observe that health subjects, after making errors, slow down their responses on the next trial (Rabbitt, 1966, Rabbitt, 1968). This can be interpreted as a sign of a control process to ensure the correct response is given. In a first study analysing error detection and post- error slowing in ADHD children, Sergeant and van der Meere (1988) found that error detection in ADHD patients was present as they were able to correct their responses. In contrast to this, no post-error slowing was found in the ADHD sample, which was explained through a limited ability of the ADHD patients to adjust their processing. The effect of reduced post-error slowing was replicated (Schachar et al., 2004) and can be improved by methylphenidate medication (Krusch et al., 1996).
In recent years, the neural correlates of error processing have been studied. In measurements of event-related electroencephalographic potentials, a specific neuroelectric signal recorded at the scalp has been described. After error trials, a negative potential with a fronto-central maximum can be found, called error negativity (Ne, Falkenstein et al., 1991) or error-related negativity (ERN, Gehring et al., 1993), which occurs within the first 100 ms after an erroneous response has been made. This negative deflection is followed by a positive component with a centro-parietal maximum peaking about 200–450 ms after the incorrect response (error-positivity, Pe, Falkenstein et al., 1991).
On a theoretical basis (Holroyd and Coles, 2002), the ERN is the neural correlate of the signal that an event is worse than expected. The Pe is thought to reflect the conscious evaluation of an error (Falkenstein et al., 2000, Nieuwenhuis et al., 2001). In a comparison of perceived and unperceived error trials in an antisaccade task, the Pe was clearly present on perceived error trials, but was remarkably reduced on unperceived error trials. In contrast, the ERN was present on unperceived and perceived error trials. Interestingly, unperceived error trials were also characterized by the absence of post-error slowing (Nieuwenhuis et al., 2001).
With regard to error processing in ADHD, some inconsistencies are still present (Ullsperger, 2006). In a recent stop-signal task study in 10 ADHD children (combined subtype, on chronic methylphenidate medication and off medication for just 1 night), a reduced ERN was found, without any changes in the corresponding Pe (Liotti et al., 2005). In contrast, Wiersema et al. (2005) found reduced Pe amplitudes with a corresponding reduction of post-error slowing but no changes for the ERN in 22 ADHD children (combined subtype, 11 on chronic methylphenidate medication and off medication for 24 h). A recent study with 10 ADHD children and 10 healthy control children confirmed this pattern and found that the ERN amplitude was unaffected and Pe amplitude was reduced in the ADHD group (Jonkman et al., 2007). These inconsistencies indicate the need for more research on the neural correlates of error processing in ADHD.
Influenced by a recent study (Potts et al., 2006) that explored the correlation between the neural correlates of error processing (ERN and Pe) and an ADHD-relevant personality dimension (impulsivity) in healthy subjects, the aim of our study was to investigate the neural correlates of error processing in healthy young subjects and correlate it with the amount of ADHD symptoms assessed on the World Health Organization Adult ADHD Self-Report Scale (ASRS, Kessler et al., 2005).
Section snippets
Subjects
We investigated 56 subjects (33 female and 23 male subjects) with a mean age of 27.0 ± 6.8 years (ranging from 20 to 47 years of age). None of them were formerly or currently in neurological or psychiatric therapy; all of them were free of medication and right-handed. All subjects gave their written informed consent after the procedures had been fully explained.
Assessment of ADHD symptoms with the ASRS
The ASRS is an 18-item scale (Kessler et al., 2005) and is based on the criteria for ADHD from the DSM-IV-TR (American Psychiatric
Results
As expected, we found two components which differed between correct and incorrect responses in the response-locked ERPs. For the ERN we found a main effect condition (F(1,55) = 84.0, P < 0.001), a main effect localisation (F(2,110) = 67.1, P < 0.001) and an interaction effect condition × localisation (F(2,110) = 52.5, P < 0.001). The main effect condition was explained by more negative amplitudes after incorrect responses (M = − 2.42) compared with correct responses (M = 0.12).
The ERN (amplitude difference
Discussion
In this study we clearly replicated the two components of error processing, the ERN and the Pe (Falkenstein et al., 1991, Gehring et al., 1993). Most interestingly, we found an association of these neural correlates of error processing and the ratings of ADHD symptoms in healthy participants. In more detail, the amplitudes of the Pe after incorrect responses were negatively correlated with the ratings of ADHD symptoms on the inattentive scale of the ASRS. That means that subjects with higher
Acknowledgement
This study was supported by the Deutsche Forschungsgemeinschaft (KFO 125/1-1).
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