The Specificity of Inhibitory Control Deficits in Post-Traumatic Stress Disorder: A Dissociation Between the Speed and Reliability of Stopping

Abstract

Inhibitory control over thoughts, emotions, and actions is challenging for people with Post-Traumatic Stress Disorder (PTSD). Whether specific aspects of inhibitory control are differentially affected in PTSD remains an open question. Here we examined performance on two popular response inhibition tasks in 28 combat Veterans with PTSD and 27 control Veterans. We used a Hybrid variant that intermixed 75% Go trials, 12.5% NoGo trials, and 12.5% Stop trials. Parameters from an ex-Gaussian race model (Matzke et al., 2017) provided estimates of stopping speed (μ Stop) and stopping variability (τ Stop). Participants with PTSD had higher error rates on NoGo trials, replicating previous results. The estimated probability of "trigger failures" (failures to launch inhibitory control) on Stop trials was also higher in PTSD patients, suggesting that sustained attention was a common deficit in the two tasks. Stopping variability was also increased in participants with PTSD, which supports a difficulty with maintaining task goals. Conversely, stopping speed did not differ between patients and controls, suggesting that core inhibitory processes were intact. These results demonstrate a dissociation between the speed and reliability of motor response inhibition in PTSD, and suggest that top-down inhibitory control was deployed less consistently in participants with PTSD.

Keywords: Cognitive Control; Executive Control; Go/NoGo; PTSD; Response Inhibition; Stop-signal.

Fig. 1.

Bayesian ex-Gaussian race model with a go runner and a stop runner (triggered by Go stimuli and Stop stimuli, respectively). NoGo trials are not included in the model. Adapted from Figure 1 of Matzke, Curley, Gong, and Heathcote (2019). Original available at https://www.flickr.com/photos/156287181@N04/28061794878/in/dateposted-public/ under CC BY 2.0 license, https://creativecommons.org/licenses/by/2.0/

Fig. 2.

Errors Involving a Failure to Activate the Stopping Process in Participants with PTSD and Controls. Errors of commission on NoGo trials, compared to estimated Trigger Failures on Stop trials.

Fig. 3.

Correlations between PTSD Symptom Severity and Parameters from the Bayesian Ex-Gaussian Model. The outlier in the sigma Stop panel depicts data from a control; removing this person did not affect the outcome.