Background: We examined P300 measures in patients with posttraumatic stress disorder (PTSD) and control subjects at two different time points to determine event-related potential (ERP) stability over time and the relationship of changes in ERPs to changes in symptom levels.
Methods: Auditory and visual P300 was recorded in a three-condition novelty oddball task in 25 male subjects with combat-related PTSD and 15 male combat-exposed normal control subjects at two time points separated by 6-12 months. Regression analyses were conducted to compare the temporal stability of ERP measures in PTSD and control subjects. Variability in ERP measures over time within PTSD subjects was examined for association with changes in symptom levels.
Results: There were no significant differences in P300 amplitude or latency in PTSD versus control subjects at either time point, regardless of stimulus type (target, novel) or modality (auditory, visual). Nine of 24 P300 measures were significantly less predictable over time in the PTSD group compared to control subjects. Variability of P300 measures over time was not associated with fluctuations in symptoms of depression or PTSD.
Conclusions: P300 ERPs are more variable cross-sectionally and over time in PTSD subjects compared to trauma exposed control subjects. Measures of variability about the group mean appear to be more informative about the cognitive electrophysiology of PTSD than measures of central tendency.