Posted 07.23.2019 | by AMRA

Overcoming irrational fears involves recognizing when stimuli previously associated with danger have ceased their association with that danger. This means “extinguishing” a learned connection between a stimulus and its previously feared negative consequences.

Mindfulness can help with fear extinction by enabling individuals to approach previously feared stimuli with an attitude of non-reactive acceptance. Sevinc et al. [Biological Psychiatry] studied whether a mindfulness-based intervention affects the brain activity underlying the fear extinction process.

The researchers assigned 94 meditation-naive adults (average age = 32 years; 64% female) to either an 8-week mindfulness-based stress reduction (MBSR) program or an 8-week exercise-based stress management education program. Stress education consisted of 8 weekly 2 hour group sessions that included 40 minutes of light aerobic exercise and didactic presentations on coping with stress through exercise, nutrition, humor, and sleep hygiene.

Two weeks before and after intervention, participants underwent a two-day classical fear conditioning and fear extinction paradigm while being monitored by brain imaging (fMRI).

In the fear conditioning paradigm, participants were presented with images of rooms with either red, blue, or yellow lights. An annoying electric shock immediately followed the images of the rooms with the red or blue lights, but not the yellow lights. Fear was considered “conditioned” to the red or blue lights when exposure to those images led to an increase in skin conductance.

After the conditioned skin conductance response (SCR) was acquired, participants were then repeatedly exposed to the image with the red light without a consequent shock in order to extinguish the skin conductance response to that image while maintaining the conditioned skin conductance response to the blue light.

The next day, participant SCRs to the images were reassessed in a “recall” session. The researchers were testing if the SCR to the red light remained extinguished while those to the blue light remained intact. The researchers were interested in the role of the hippocampus during these trials and how it functionally related to other brain regions. The hippocampus is a brain region that is critically involved in the contextual encoding and retrieval of fear extinction memories.

Participants were also administered measures of perceived stress, anxiety, emotional regulation difficulties, and mindfulness before and after the intervention.

The results showed that both MBSR (Cohen’s d=0.56) and stress education (d=0.57) significantly reduced perceived stress. There was also a marginal advantage (p=.05; partial η2=0.63) for MBSR for anxiety reduction. There were no significant group differences in stress, emotional regulation, or mindfulness.

Significant relationships were found between a number of brain structures and the retention of extinction learning. Higher baseline hippocampal activity was associated with better retention of extinction learning (r=.79). While there was no significant difference in extinction retention between groups, only MBSR participants significantly improved their extinction retention at post-intervention.

MBSR participants also showed significantly increased supramarginal gyrus activity while recalling extinguished stimuli, and this increased activity was positively correlated with MBSR home practice (r=.38).

MBSR participants also displayed increased functional connectivity between the left hippocampus and the right supramarginal gyrus, while stress education participants did not. The supramarginal gyrus is part of the brain’s memory retrieval network.

MBSR resulted in increased functional coupling between the hippocampus and the portion of the sensory cortex associated with the hand that had been administered the shocks. Post-MBSR increases in hippocampal gray matter were associated with increased connectivity between the hippocampus and the left dorsolateral prefrontal and retrosplenial cortices, two regions previously implicated in the recall of fear extinction.

The results show that while MBSR and stress education both reduce stress, MBSR has unique effects on how the brain processes fear extinction. MBSR induces changes in hippocampal structure and functional connectivity that enhance the retention of fear extinction. These changes highlight one way in which mindfulness helps to regulate emotions and reduce stress and anxiety.

Reference:

Sevinc, G., Hölzel, B. K., Greenberg, J., Gard, T., Brunsch, V., Hashmi, J. A., . . . Lazar, S. W. (2019). Strengthened hippocampal circuits underlie enhanced retrieval of extinguished fear memories following mindfulness training. Biological Psychiatry.

[Link to study]