Emotional Numbing is Associated With Reduced Pain Processing in the Amygdala

Background
Posttraumatic stress disorder (PTSD) is often associated with altered pain perception such as higher pain threshold. While pain consists of both physiological and emotional components, the latter is often overlooked. A hallmark feature of PTSD is emotional numbing (EN): restricted capacity to experience positive/negative emotions. As both EN and emotional processing of pain converge in the amygdala, here we examine whether individuals diagnosed with PTSD show lower activation to pain in the amygdala compared with combat controls, and whether amygdala response is correlated with EN, using data from two different studies.
Methods
Two samples of veterans (study 1: 37 total (18 PTSD); study 2: 48 total (26 PTSD)) underwent threat conditioning, where a conditioned stimulus (CS+; visual stimulus) was paired with an unconditioned stimulus (US; electric shock). Amygdala activity to the CS+US was contrasted with CS+ alone presentations and was correlated with EN scores.
Results
In both studies, the PTSD group showed a robust reduction in amygdala reactivity to shock compared to controls (89 %HPDi [-.41, -.02]; study 2: [-6, -.05]). Furthermore, reduced amygdala activation was negatively correlated only with EN symptoms (89% HPDi [-.30, -.02]; study 2: [-8.7, -.00]).
Conclusions
The amygdala response to pain is lower in individuals with PTSD. EN is associated with reduced pain processing in the amygdala. This altered pain processing may drive the emotional component of processes such as stress-induced analgesia. Lower amygdala reactivity to mild pain may contribute to the “all-or-none” reaction to stressful situations in PTSD.