Increased response variability as a marker of executive dysfunction in veterans with post-traumatic stress disorder.

The stability of cognitive control processes over time can be indexed by trial-to-trial variability in reaction time (RT). Greater RT variability has been interpreted as an indicator of executive dysfunction, inhibitory inefficiency, and excessive mental noise. Previous studies have demonstrated that combat veterans with post-traumatic stress disorder (PTSD) show substantial impairments in inhibitory control, but no studies have examined response variability in this population. In the current experiment, RT variability in the Go/NoGo response inhibition task was assessed for 45 veterans with PTSD and 34 control veterans using the intra-individual coefficient of variation (ICV) and ex-Gaussian analysis of RT distributions. Despite having mean RTs that were indistinguishable from controls, the PTSD patients had significantly greater RT variability as measured by ICV. More variable RTs were in turn associated with a greater number of false alarm errors in the patients, suggesting that less consistent performers were less successful at inhibiting inappropriate responses. RT variability was also highly correlated with self-reported symptoms of PTSD, depression, and attentional impulsiveness. Furthermore, response variability predicted diagnosis even when controlling for PTSD symptom severity. In turn, PTSD severity was correlated with self-rated attentional impulsiveness. Deficits in the top-down cognitive control processes that cause greater response variability might contribute to the maintenance of PTSD symptomology. Thus, the distractibility issues that cause more variable reaction times might also result in greater distress related to the trauma.