BACKGROUND:

The real-world effectiveness of exposure-based therapies for youth depends on the willingness and ability of young people to tolerate confronting their fears, which can be experienced as highly aversive and create problems with treatment engagement and acceptance. Recently, neuroscientific research on the nonconscious basis of fear has been translated into novel exposure interventions that bypass conscious processing of feared stimuli and that thus do not cause phobic youth to experience distress. We present a review of these unconscious exposure interventions.

METHODS:

A PRISMA-based search yielded 20 controlled experiments based on three paradigms that tested if fear-related responses could be reduced without conscious awareness in highly phobic, transition-age youth 14 randomized controlled trials (RCTs), 5 fMRI studies (1 was also an RCT), 4 psychophysiological studies (3 were also RCTs), and 1 ERP study. We conducted meta-analyses of outcomes where feasible.

RESULTS:

Unconscious exposure interventions significantly (1) reduced avoidance behavior (range of Cohen's d = 0.51-0.95) and self-reported fear (d = 0.45-1.25) during in vivo exposure to the feared situation; (2) reduced neurobiological indicators of fear (d = 0.54-0.62) and concomitant physiological arousal (d = 0.55-0.64); (3) activated neural systems supporting fear regulation more strongly than visible exposure to the same stimuli (d = 1.2-1.5); (4) activated regions supporting fear regulation that mediated the reduction of avoidance behavior (d = 0.70); (5) evoked ERPs suggesting encoding of extinction memories (d = 2.13); and (6) had these effects without inducing autonomic arousal or subjective fear.

CONCLUSIONS:

Unconscious exposure interventions significantly reduce a variety of symptomatic behaviors with mostly moderate effect sizes in transition-age youth with specific phobias. fMRI and physiological findings establish a neurophysiological basis for this efficacy, and suggest it occurs through extinction learning. Unconscious exposure was well tolerated, entirely unassociated with drop out, and is highly scalable for clinical practice. However, a number of limitations must be addressed to assess potential clinical impacts, including combining unconscious exposure with exposure therapy to boost treatment acceptance and efficacy.