Neurobiological interpretation of P3AR associated with externalizing psychopathology is complicated. Target P3 (or "P3b"; see Polich, 2007) is commonly studied using a stimulus “oddball” task whereby participants are instructed to attend (e.g., button-press) to infrequent target stimuli and ignore frequent non-target stimuli. During the task, electroencephalogram (EEG) is recorded to measure the brain-generated electrical field at numerous locations on the scalp. Fluctuations in this electrical field are driven by the synchronized activation of post-synaptic currents of pyramidal neurons in the cortex (Buzsaki et al., 2012). Cross-trial averaging of stimulus-locked EEG produces a waveform characterized by three positive deflections; the third of these peaks (P3) occurs roughly 300 to 600 milliseconds following stimulus-onset. Augmentation of P3 is thought to reflect the focused activation of neurotransmitter systems to promote attentional gain, stimulus evaluation, and response selection; therefore, decrements in P3 amplitude might mark deficiencies in this process (Nieuwenhuis et al., 2005; Polich, 2007).
