Current Status of Neurofeedback for Post-traumatic Stress Disorder: A Systematic Review and the Possibility of Decoded Neurofeedback

Abstract

Background: Post-traumatic stress disorder (PTSD) is a neuropsychiatric affective disorder that can develop after traumatic life-events. Exposure-based therapy is currently one of the most effective treatments for PTSD. However, exposure to traumatic stimuli is so aversive that a significant number of patients drop-out of therapy during the course of treatment. Among various attempts to develop novel therapies that bypass such aversiveness, neurofeedback appears promising. With neurofeedback, patients can unconsciously self-regulate brain activity via real-time monitoring and feedback of the EEG or fMRI signals. With conventional neurofeedback methods, however, it is difficult to induce neural representation related to specific trauma because the feedback is based on the neural signals averaged within specific brain areas. To overcome this difficulty, novel neurofeedback approaches such as Decoded Neurofeedback (DecNef) might prove helpful. Instead of the average BOLD signals, DecNef allows patients to implicitly regulate multivariate voxel patterns of the BOLD signals related with feared stimuli. As such, DecNef effects are postulated to derive either from exposure or counter-conditioning, or some combination of both. Although the exact mechanism is not yet fully understood. DecNef has been successfully applied to reduce fear responses induced either by fear-conditioned or phobic stimuli among non-clinical participants. Methods: Follows the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, a systematic review was conducted to compare DecNef effect with those of conventional EEG/fMRI-based neurofeedback on PTSD amelioration. To elucidate the possible mechanisms of DecNef on fear reduction, we mathematically modeled the effects of exposure-based and counter conditioning separately and applied it to the data obtained from past DecNef studies. Finally, we conducted DecNef on four PTSD patients. Here, we review recent advances in application of neurofeedback to PTSD treatments, including the DecNef. This review is intended to be informative for neuroscientists in general as well as practitioners planning to use neurofeedback as a therapeutic strategy for PTSD. Results: Our mathematical model suggested that exposure is the key component for DecNef effects in the past studies. Following DecNef a significant reduction of PTSD severity was observed. This effect was comparable to those reported for conventional neurofeedback approach. Conclusions: Although a much larger number of participants will be needed in future, DecNef could be a promising therapy that bypasses the unpleasantness of conscious exposure associated with conventional therapies for fear related disorders, including PTSD.

Keywords: PTSD; fMRI decoded neurofeedback (DecNef); multi-voxel decoding; neural reinforcement; neuromodulation; real-time functional magnetic resonance imaging.

Figure 1

PRISMA flow-chart illustrating the results of the search strategy.

Figure 2

Schema of decoded neurofeedback. The participant, in the scanner, is instructed to “somehow” regulate their brain activities so that the feedback is maximized. Then, “somehow” manipulated brain activity pattern are processed as a fMRI signal and compared with target brain activity pattern. Finally, the participants are presented with a disk whose size is in proportion to the likelihood, which is also in proportion to the amount of reward the participant will gain from that trial. This cycle is then repeated. The figure is adopted from Yamada et al. (2017), with no permission required.

Figure 3

DecNef effects on fear reduction in (A) fear-conditioned stimuli and (B) feared animals. The response to target stimuli was reduce compared to control stimuli in both (A) fear-conditioned stimuli and (B) feared animals as measured by both amygdala activity and skin conductance response (SCR). Error bars represent standard errors. (A) Modified from Koizumi et al. (2016), with permission from the authors. (B) Modified from Taschereau-Dumouchel et al. (2018), with no permission required. ^*p < 0.05.

Figure 4

DecNef effects on PTSD amelioration. PTSD symptom cluster (i.e., re-experiencing, avoidance, and hypervigilance) and total severity scores as measured by the past week version of the CAPS-4. The re-experiencing symptoms and hypervigilance symptoms, as well as total PTSD severity at pre DecNef session reduced significantly compared at post-DecNef session. Error bars represent standard errors.

Figure 5

Comparison between predicted value and experimental value of Amygdala reactivity post-DecNef (target–control). Black dot indicates the individual data from Koizumi et al. (2016) while the white dot indicates the individual data from Taschereau-Dumouchel et al. (2018).