Of course, the present review highlights the possibility that a reduced ERN might also relate to the externalizing dimension of personality and psychopathology; however, further research needs to be done to confirm and extend these findings. Future studies might clarify other remaining issues. For example, more studies are needed to assess changes in ERN amplitude after successful treatment in order to tease apart state and trait influences on the ERN. Some studies have already suggested that trait-related differences in anxiety relate to an increased ERN, whereas no studies have similarly examined the impact of state-related depressive changes on the ERN. Finally, longitudinal studies beginning in childhood are necessary to examine the ERN in children prior to the development of psychiatric disorders to establish a time-line for when differences in ERN amplitude begin to signify risk.
