Do EEG and startle reflex modulation vary with self-reported aggression in response to violent images?

Increased violence and aggressive tendencies are a problem in much of the world and are often symptomatic of many other neurological and psychiatric conditions. Among clinicians, current methods of diagnosis of problem aggressive behaviour rely heavily on the use of self-report measures as described by the Diagnostic and Statistical Manual of Mental Disorders 5th Edition (DSM-5) and International Classification of Diseases 10th revision (ICD-10). This approach does not place adequate emphasis on objective measures that are potentially sensitive to processes not feeding into subjective self-report. Numerous studies provide evidence that attitudes and affective content can be processed without leading to verbalised output. This exploratory study aimed to determine whether individuals in the normal population, grouped by self-reported aggression, differed in subjective versus objective affective processing. Participants (N = 52) were grouped based on their responses to the Buss–Durkee Hostility Inventory. They were then presented with affect-inducing images while brain event-related potentials (ERPs) and startle reflex modulation (SRM) were recorded to determine non-language-based processes. Explicit valence and arousal ratings for each image were taken to determine subjective affective effects. Results indicated no significant group differences for explicit ratings and SRM. However, ERP results demonstrated significant group differences between the ‘pleasant’ and ‘violent’ emotion condition in the frontal, central and parietal areas across both hemispheres. These findings suggest that parts of the brain process affective stimuli different to what conscious appraisal comes up with in participants varying in self-reported aggression.