Brain-based mediation of non-conscious reduction of phobic avoidance in young women during functional MRI: a randomised controlled experiment

Siegel, Wang, Murray, Campos et al. (2020) conducted a randomized, placebo-controlled test of unconscious exposure during fMRI scanning.

“Siegel, Wang, Murray, Campos et al. (2020) addressed these limitations by conducting a randomized, placebo-controlled test of unconscious exposure during fMRI scanning.”

VBE strongly activated frontostriatal circuits both in phobic relative to control participants and relative to placebo within phobic participants.

“In particular, VBE strongly activated frontostriatal circuits (including caudate, thalamus, inferior frontal gyrus, dorsal anterior cingulate cortex (dACC), premotor regions) both in phobic relative to control participants, and relative to placebo exposure within phobic participants.”

In the Siegel et al. 2020 study, VBE to masked spiders strongly activated brain regions supporting emotion, emotion regulation, attention, and visual pattern recognition in phobic relative to control participants.

“VBE strongly activated brain regions supporting emotion (amygdala, parahippocampus, orbital frontal cortex), emotion regulation (medial prefrontal cortex (PFC), frontostriatal regions), attention (dorsal lateral PFC, superior parietal cortices), and visual pattern recognition (fusiform gyrus) in phobic relative to control participants.”

In a stricter comparison, VBE activated most of the same regions relative to placebo exposure within phobic participants.

“In a stricter comparison, VBE activated most of the same regions relative to placebo exposure within phobic participants.”

Behaviorally, VBE did not cause phobic participants to experience fear and subsequently reduced their avoidance of a live tarantula relative to placebo exposure.

“Behaviorally, VBE did not cause phobic participants to experience fear, and it subsequently reduced their avoidance of a life tarantula relative to placebo exposure.”

Siegel et al. (2020) did not manipulate awareness of exposure by including a visible exposure group, which is necessary to discern awareness-based cause-effect relationships between unconscious exposure and fear-related responses.

“Siegel et al. (2020) did not manipulate awareness of exposure by including a visible exposure group, which is necessary to discern awareness-based, cause-effect relationships between unconscious exposure and fear-related responses.”

The ventral medial PFC partially mediated the effect of VBE on reducing phobic avoidance (Siegel et al. 2020).

“The ventral medial (vm) PFC, which subserves the retention of extinction learning (Phelps et al. 2004), partially mediated the effect of VBE on reducing phobic avoidance (Siegel et al. 2020).”

These frontostriatal systems partially mediated the effect of VBE on reducing phobic avoidance (Siegel et al. 2020).

“These frontostriatal systems partially mediated the effect of VBE on reducing phobic avoidance (Siegel et al. 2020).”

Siegel et al. (2020) did not record changes in physiological arousal, which is crucial for selecting between potential mechanisms of unconscious exposure.

“Siegel et al. (2020) also did not record changes in physiological arousal, which as we describe in the Discussion is crucial for selecting between potential mechanisms of unconscious exposure.”

Evidence suggests that CBT or medication can modify the cascade of responses to real or perceived threat - CBT by altering behavioral avoidance and information processing related to threat detection and coping, and medication by altering neurotransmitter levels that affect the function and structure of brain circuits.

“Evidence suggests that CBT or medication can modify the cascade of responses to real or perceived threat – CBT by altering behavioral avoidance and information processing related to threat detection and coping [56, 57], and medication by altering neurotransmitter levels that affect the function and structure of brain circuits [58–60].”

Extinction activates neural pathways that inhibit or modulate emotional responses and avoidance of the feared stimulus.

“Extinction activates neural pathways that inhibit or modulate emotional responses and avoidance of the feared stimulus [57].”