Discussion
dissociative drug, PTSD
The present randomized-controlled pilot study examined effects of ketamine, a dissociation-inducing drug (Feder et al. Initial observations of increased (top-down) fronto-limbic RSFC in individuals with the dissociative subtype of PTSD (Nicholson et al. By pharmacologically manipulating dissociation, our study adds a new angle to the understanding of the link between dissociation and fronto-limbic RSFC in PTSD. However, as our study extends previous work in various aspects, we cannot yet determine why exactly our results deviate from previous findings. One essential advantage differentiating the current from previous studies is the study design. Previous correlative findings (Nicholson et al. This study also differs from others in the circumstances under which dissociation was observed. Here, we employed a dissociative drug to examine RSFC alterations independently from circumstances accompanying naturally occurring dissociation. In contrast, in previous observational studies (Nicholson et al. Last, it could also be that diverging findings are related to different neurotransmitter systems involved in ketamine-induced and naturally occurring dissociation. As Salvia divinorum, an opioid receptor agonist, has been shown to produce an altered state of consciousness similar to dissociative symptoms (Addy et al. Altogether, evidence on the relationship between dissociation and fronto-limbic RSFC is mixed, including positive (Nicholson et al. Despite the promising nature of the current preliminary findings, several limitations of the current work should be noted. First, we did not assess dissociation experience during or directly after the infusion taking place in the fMRI. However, a large body of studies has documented ketamine’s dissociative effect in healthy and clinical populations (Krystal 