Posted 08.19.2020 | by AMRA

Mindfulness training can reduce anxiety for some people, yet it is not fully clear how it operates. At the neural level, the brain’s hippocampus is one possible target given its involvement in learning to be afraid when in danger, and unlearning fear once danger is gone. Mindfulness-induced hippocampal changes may play a critical role in anxiety reduction.

Sevinc et al. [Brain and Behavior] tested mindfulness training against a stress management intervention on hippocampal volume and hippocampal connectivity to other brain regions during fear conditioning and extinction.

The researchers randomly assigned 89 participants (female=64%; average age=32 years) to either Mindfulness-Based Stress Reduction (MBSR) or Stress Management Education as a control group. The control group consisted of didactic presentation and discussion of nutrition, exercise, sleep hygiene, coping skills, and humor. Both 8-week interventions were delivered in weekly 2-hour group sessions, and both were assigned 40-minutes of daily homework (strength training and aerobic exercise for the control group) and a 4-hour intensive session in week six.

Before and after the intervention, all participants underwent fMRI scanning on two consecutive days. On the first day, the researchers induced a classically conditioned fear response by exposing participants to three neutral stimuli (pictures of different colored lamps) and pairing two of them with an annoying electrical shock delivered to their fingers. On the second day, one of the conditioned fear responses was extinguished by exposing participants to the same colored lamp stimuli, but only pairing one color with the electrical shock.

While participants underwent the fear conditioning and extinction activities, the researchers measured their hippocampal volumes and hippocampal connectivity with other brain regions. Participants also completed self-report measures of psychological variables before and after the intervention.

A previously published portion of this study showed that both groups significantly reduced their stress levels (d=0.56), and there was a trend towards greater anxiety reduction in the MBSR group (partial η2=0.63).

Results showed that the MBSR group had increased volume in a region of the hippocampus (the subiculum) after the intervention. The increase in volume was significantly associated with a decrease in functional connectivity between the left hippocampus and regions of the visual cortex during conditioned fear extinction. This makes sense because conditioned fear extinction involved unlearning of the previously learned connections between the colored lamps and the shock. These changes in hippocampal-visual cortex connectivity were significantly correlated with decreases in self-reported anxiety levels (r=-.39).

The study shows that mindfulness training impacts hippocampal size and connectivity in a manner associated with decreases in felt anxiety. Hippocampal changes suggest mindfulness training functions, in part, as an “exposure therapy,” extinguishing anxiety reactions though non-judgmental attention to associated thoughts and feelings. The smaller sample size of the control group may have limited detection of significant within-group effects for the controls.

Reference:

Sevinc, G., Greenberg, J., Hölzel, B. K., Gard, T., Calahan, T., Brunsch, V., Hashmi, J. A., Vangel, M., Orr, S. P., Milad, M. R., & Lazar, S. W. (2020). Hippocampal circuits underlie improvements in self-reported anxiety following mindfulness training. Brain and Behavior.

[Link to study]