•Weak/strong prepulses induced weak/strong prepulse inhibition (PPI) of startle reflex.•Tones detected after strong PPI trials elicited relatively higher N1 and smaller P3.•Eyeblink-PPI influenced primary psychopathy through the mediation of Defensive-Fight.•High Def-Fight scorers displayed relatively larger N1 waves to target tones. This study examined the associations between Reinforcement Sensitivity Theory (RST-PQ, Corr & Cooper, 2016) and psychopathy traits (LSRPS, Levenson et al., 1995) in university students. The aim was to identify psychopathy and RST traits associated with prepulse inhibition (PPI) of acoustic startle and ERP responses by using two prepulse-stimulus intensities (70 and 85 dB) combined with a 105 dB startle pulse (200 ms prepulse-plus-pulse interval). The higher intensity prepulse produced a larger PPI, although both prepulse stimuli reliably activated the startle system. Higher Primary Psychopathy was associated with a higher Defensive-Fight trait and both measures were associated with larger PPI. A principal components factor analysis disclosed an N1-startle factor that was a significant predictor of both reward reactivity and Goal-Drive Persistence scores. Results appear in line with Newman’s response modulation hypothesis emphasizing the engagement of attention and recognition of stimulus salience, which may be disrupted in psychopathy.