Learning to Obtain Reward, but Not Avoid Punishment, Is Affected by Presence of PTSD Symptoms in Male Veterans: Empirical Data and Computational Model

Post-traumatic stress disorder (PTSD) symptoms include behavioral avoidance which is acquired and tends to increase with time. This avoidance may represent a general learning bias; indeed, individuals with PTSD are often faster than controls on acquiring conditioned responses based on physiologically-aversive feedback. However, it is not clear whether this learning bias extends to cognitive feedback, or to learning from both reward and punishment. Here, male veterans with self-reported current, severe PTSD symptoms (PTSS group) or with few or no PTSD symptoms (control group) completed a probabilistic classification task that included both reward-based and punishment-based trials, where feedback could take the form of reward, punishment, or an ambiguous “no-feedback” outcome that could signal either successful avoidance of punishment or failure to obtain reward. The PTSS group outperformed the control group in total points obtained; the PTSS group specifically performed better than the control group on reward-based trials, with no difference on punishment-based trials. To better understand possible mechanisms underlying observed performance, we used a reinforcement learning model of the task, and applied maximum likelihood estimation techniques to derive estimated parameters describing individual participants’ behavior. Estimations of the reinforcement value of the no-feedback outcome were significantly greater in the control group than the PTSS group, suggesting that the control group was more likely to value this outcome as positively reinforcing (i.e., signaling successful avoidance of punishment). This is consistent with the control group’s generally poorer performance on reward trials, where reward feedback was to be obtained in preference to the no-feedback outcome. Differences in the interpretation of ambiguous feedback may contribute to the facilitated reinforcement learning often observed in PTSD patients, and may in turn provide new insight into how pathological behaviors are acquired and maintained in PTSD

Respiratory and cardiovascular response during electronic control device (ECD) exposure in law enforcement trainees

Objective: Law enforcement represents a large population of workers who may be exposed to electronic control devices (ECDs). Little is known about the potential effect of exposure to these devices on respiration or cardiovascular response during current discharge. Methods: Participants (N=23) were trainees exposed to 5 seconds of an ECD (Taser X26®) as a component of training. Trainees were asked to volitionally inhale during exposure. Respiratory recordings involved a continuous waveform recorded throughout the session including during the exposure period. Heart rate was calculated from a continuous pulse oximetry recording. Results: The exposure period resulted in the cessation of normal breathing patterns in all participants and in particular a decrease in inspiratory activity. No significant changes in heart rate during ECD exposure were found. Conclusions: This is the first study to examine breathing patterns during ECD exposure with the resolution to detect changes over this discrete period of time. In contrast to reports suggesting respiration is unaffected by ECDs, present evidence suggests that voluntary inspiration is severely compromised. There is no evidence of cardiac disruption during ECD exposure

Performance on reward and punishment trials.

<p>(A) There was considerable individual variation in performance on reward trials, and no correlation between performance on reward and punishment trials. Vertical and horizontal lines represent chance performance (50%); note 11 participants who made less than 35% optimal responses on reward trials (dashed line) – i.e. reliably chose the <i>non-optimal</i> response on reward trials. (B) On reward trials, the PTSS group significantly outperformed the control group (<i>F</i>(1,65) = 6.43, <i>p</i> = 0.014) but there was no group difference on punishment trials. (C) There was no significant effect of psychoactive medication status in the control group, which specifically excluded participants self-reporting use of antidepressant medications. (D) In the PTSS group, there were no significant differences among those reporting no medication (“No Med”), antidepressant use (“Antidepressant”), or use of psychoactive drugs excluding antidepressants (“Psychoactive”).</p

Category and feedback structure of the probabilistic reward and punishment learning task.

<p>Category and feedback structure of the probabilistic reward and punishment learning task.</p

Example screen events from the behavioral task.

<p>(A) On each trial, the participant sees a stimulus and is asked to categorize that stimulus as “A” or “B”. The chosen category is circled, and corrective feedback may appear. For some stimuli (punishment trials), incorrect classification is punished with point loss (B) while correct classification receives no feedback (C); for other stimuli (reward trials), correct classification is rewarded with point gain (D) while incorrect classification receives no feedback. The task is probabilistic, so a stimulus does not belong to the same category on every trial (refer <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0072508#pone-0072508-t001" target="_blank">Table 1</a>).</p

Mean (and SD) of age and education, and questionnaire scores, in the control and PTSS groups.

<p>Asterisk indicates significant difference between PTSS and control groups (<i>t</i>-test, <i>p</i><0.001).</p

Performance on the behavioral task.

<p>(A) Overall, the PTSS group achieved higher total points than the control group (<i>F</i>(1,65) = 5.75, <i>p</i> = 0.019). (B) There was an interaction of combat history with medication status. Specifically, among those without combat history, those on current psychoactive medications outperformed non-medicated peers (<i>t</i>(50) = 2.34, <i>p</i> = 0.024).</p