Blunted responses to reward in remitted post-traumatic stress disorder

Abstract

Background: Recent evidence suggests blunted responses to rewarding stimuli in patients with post-traumatic stress disorder (PTSD). However, it is not clear whether these alterations in reward processing normalize in remitted PTSD patients.

Methods: We tested behavioral and physiological responses to monetary reward in a spatial memory task in 13 accident survivors with remitted PTSD, 14 accident survivors who never had PTSD, and 16 nontrauma-exposed subjects. All accident survivors were recruited from two samples of severely physically injured patients, who had participated in previous prospective studies on the incidence of PTSD after accidental injury approximately 10 years ago. Reaction time, accuracy, skin conductance responses, and self-reported mood were assessed during the task.

Results: Accident survivors who never had PTSD and nontrauma exposed controls reported significantly higher positive mood in the reinforced versus nonreinforced condition (P < 0.045 and P < 0.001, respectively), while there was no effect of reinforcement in remitted PTSD subjects.

Conclusions: Our findings suggest an alteration of the reward system in remitted PTSD. Further research is needed to investigate whether altered reward processing is a residual characteristic in PTSD after remission of symptoms or, alternatively, a preexisting risk factor for the development of PTSD after a traumatic event.

Keywords: Experimental; motivation; post-traumatic stress disorder; psychopathology; remitted; residual symptoms; reward.

Figure 1

Illustration of a rewarded trial of the spatial delayed recall task at the easiest level of difficulty. In the first display, an array of yellow circles (3, 5 or 7) is presented for 2000 ms after a fixation time of 500 ms. After a delay of 3000 ms, a green circle appears and the subject has 3000 ms to decide whether the position of the green circle is the same as one of the preceding yellow circles by pressing two different buttons. After the subject has responded or the response time has elapsed, the circle disappears and the feedback and accumulated amount of earned money appears on the screen (in the rewarded condition) or the screen remains blank (in the unrewarded condition). During the rewarded condition, participants can earn a monetary reward for every correct response. The monetary reward increased according to the difficulty of the task. During the nonreinforced condition, participants eceive no feedback on their answer. The positions of the circles varied randomly and were organized according to a 5 × 5 grid dividing the space into 25 possible positions.

Figure 2

Plot of the reaction time and mood ratings across the different conditions of the task for each group of participants. (A) Reaction times: Across groups, the reaction times were slower with increasing difficulty and shorter for the reinforced condition. The nontrauma group showed the shortest reaction times and the longest reaction times were shown by the trauma controls. (B) Mood ratings: We found a significant group x reinforcement interaction (F = 3.49, P = 0.03) that is expressed by an effect of reinforcement in the trauma control (P = 0.05) and nontrauma (P < 0.001) groups but not for the remitted PTSD group (P = 0.83).