Experiment suggests fear may be reduced with non-conscious exposure

Very brief exposure (VBE) to masked stimuli generated strong neural activation and reduced fear non-consciously in women with arachnophobia, a randomized controlled fMRI experiment suggested.

“Our findings challenge the clinical belief that direct confrontation of feared situations (and thus conscious physiological arousal and emotional distress) are necessary to reduce fear,” wrote Paul Siegel, PhD, of State University of New York in Purchase, and colleagues in Lancet Psychiatry.

“Masking exposure to phobic stimuli recruits neural circuits that support automatic fear processing and extinction in people with specific phobia, while simultaneously preventing awareness of exposure and, thus, the conscious experience of fear.”

The study compared responses to VBE (masked spiders, in this case) with responses to a control stimulus (masked flowers, or VBF) in people with arachnophobia and in controls.

VBE generated stronger neural activity in women with arachnophobia compared with controls, particularly in regions supporting emotion, emotion regulation, and attention systems, such as the inferior frontal cortex (Cohen’s d 0.95, 95% CI 0.93–0.98, Bayesian posterior probability 99.5%) and the caudate nucleus (1.16, 95% CI 1.14–1.18, 100%).

VBE also generated stronger activity in these regions than did VBF (dorsal anterior cingulate cortex Cohen’s d 0.80, 95% CI 0.78–0.80, Bayesian posterior probability 98.5%; caudate nucleus 1.0, 95% 0.98–1.02, 99.5%) in participants with arachnophobia, and reduced their avoidance of a live tarantula.

“The evidence challenges common clinical assumptions that heightened experience of aversive arousal is a necessary condition for effective change during exposure, it sheds light on mediating neural mechanisms, and it holds the promise of guiding the development of adjunct pre-exposure interventions that might help to increase exposure treatment completion rates and alleviate suffering in a larger number of individuals,” noted Ryan Smith, PhD, of Laureate Institute for Brain Research in Tulsa, Oklahoma, in an accompanying editorial.

“If their findings for VBE prove to be generalizable to a wider range of individuals and disorders, this could represent an important advance in translational neuroscience,” he added.

Anxiety disorders, including specific phobia, affect up to one-third of the population at some point in life. An important component of treatment involves exposure therapy, which includes awareness of aversive experiences that may lead to non-treatment or incomplete treatment.

Recent attention to unconscious emotion in psychiatry and clinical psychology suggests a less aversive approach. The authors of the present study previously demonstrated with spiders that VBE, in contrast to both clearly visible exposures and to a control stimulus of masked flowers, produced neural activity more strongly in phobic than non-phobic study participants. Clearly visible phobic stimuli deactivated regions associated with fear regulation and correlated with explicit fear, while VBE activation correlated with implicit fear.

Between September 2013 and August 2016, Siegel and colleagues recruited women ages 18-29 and sorted them according to the Fear of Spiders Questionnaire, a spider Stroop task (colored-word naming interference with spider-related words compared with other words), and a behavioral avoidance test.

A tarantula avoidance behavioral score was obtained for those in the phobic group a month before and shortly after the fMRI scan. The score described degrees of willingness to approach and interact with a live tarantula based on 10 progressive tasks (0=won’t enter the room; 10=expressed willingness to touch a tarantula in a terrarium).

Those in the top 10% on the Fear of Spiders Questionnaire who had impairing avoidance of the tarantula, a differential response to spider words on the Stroop test, and met criteria for specific phobia were included in the phobia group (n=42; 21 randomized to VBE and 21 to VBF). Controls (n=40; 20 randomized to VBE and 20 to VBF) had Fear of Spiders scores in the bottom 30%, no avoidance or color-naming interference, and no psychiatric disorder.

During a 10-minute fMRI task, each participant was exposed to 16 blocks of ten masked target stimuli (spiders or flowers), alternating with 16 blocks of ten masked neutral stimuli. Researchers presented the target stimulus or a neutral stimulus for 30 ms, followed immediately by a masking stimulus of capital letters for 120 ms. Participants who received VBE were unable to identify the masked spider stimuli.

A few minutes after the fMRI task, participants with arachnophobia approached the tarantula again so researchers could measure changes in phobic behavior.

Among the phobia group, VBE reduced avoidance of the tarantula more than VBF (P interaction=0.04, effect size 0.57). Avoidance test scores with VBE increased from 4.6 at baseline to 5.4. With VBF, tarantula avoidance scores increased from 4.6 to 4.8.

Following VBE, 11 (52%) participants with arachnophobia were able to get closer to the tarantula, compared with three participants (15%) after VBF.

Task-driven activation involving vision and attention was seen in all four groups. Frontostriatal activation was higher in the phobia group than controls, was greater in the phobia group for VBE vs VBF and showed a steady increase over time while activated.

Frontostriatal circuits are believed to support “among other things, the inhibition of fear responses, and the extinction of stimulus generalization,” the researchers noted. “Overall, therefore, the evidence suggests that VBE may non-consciously reduce avoidance in individuals with specific phobia by inducing fear extinction mediated by the ventral medial prefrontal cortex, supported by activation of frontostriatal regions.”

Limitations of the study include the non-unique functions of regions activated. Notably, “the clusters of activation found by Siegel and colleagues span many areas across the brain, each of which is implicated in a wide array of functions,” the editorialist wrote. “Because many areas (especially frontoparietal regions) are activated by multiple psychological processes, simply knowing that a given brain area was engaged provides insufficient information to establish the psychological process involved.”

  1. Very brief exposure to masked stimuli generated strong neural activation and reduced fear non-consciously in women with arachnophobia, a randomized controlled fMRI experiment suggested.

  2. Findings challenge the clinical belief that direct confrontation of feared situations is necessary to reduce fear, the researchers said.

Paul Smyth, MD, Contributing Writer, BreakingMED™

This study was funded by an NIH grant and a Brain & Behavior Research Foundation Young Investigator Award.

Researchers declared no competing interests.

The editorialist declared no competing interests.

Cat ID: 146

Topic ID: 87,146,130,192,146,52,925