- In a randomized study of healthy volunteers, functional activity in the right supramarginal gyrus during extinction recall was higher in participants who had mindfulness training than in those who engaged in an exercise-based stress reduction program
- Compared with the control group, participants who had mindfulness training showed increased connectivity between the hippocampus and the supramarginal gyrus during the early phase of extinction recall
- The mindfulness group demonstrated increased connectivity between the hippocampus and right primary sensory cortex
- Increases in hippocampal gray matter intensity following mindfulness training predicted enhanced connectivity between the hippocampus, dorsolateral prefrontal cortex and retrosplenial cortex
- Extinction learning is a plausible mechanism through which mindfulness training may foster resilience and reduce stress and anxiety
Regulation of emotional expression is essential for mental health, and a major component is the ability to recall that a stimulus is no longer associated with a threat. This ability is the basis for exposure-based therapies for phobia, trauma and other anxiety disorders.
Similarly, in mindfulness meditation, trainees are taught to bring their attention to present-moment sensory experience with an accepting and nonjudging attitude. In previous research published in Perspectives on Psychological Science, Sara W. Lazar, PhD, a research associate in the Department of Psychiatry at Massachusetts General Hospital, and colleagues proposed that this process facilitates "extinction learning," in which a conditioned response to a stimulus decreases when the reinforcer is omitted.
Extinction learning occurs in three phases: acquisition, consolidation and retrieval. The hippocampus is critical to consolidation and retrieval because it gates the expression of either the conditioned fear or—beneficially—the extinction memory, depending on contextual information.
Now, Dr. Lazar, research fellow Gunes Sevinc, PhD, and colleagues have demonstrated in a randomized, controlled study that mindfulness training alters hippocampal functioning during the retrieval process, leading to improvements in the extinction of fearful associations. Their report appears in Biological Psychiatry.
The researchers studied 67 neurologically and psychiatrically healthy subjects ages 8 to 50 years from the community. Subjects could not have taken more than four meditation classes of any kind in the past year or more than 10 classes in their lifetime. There were no significant differences between groups in terms of gender, age or years of education.
The subjects were randomly assigned to engage in a mindfulness-based or exercise-based stress-reduction program for eight weeks. There were 42 participants in the mindfulness group and 25 in the exercise group. The two groups were offered the same amount of contact with instructors and were assigned the same amount of home practice.
Before and after the stress-reduction program, all subjects participated in a two-day fear conditioning and extinction protocol previously reported by Mass General researchers in Biological Psychiatry using a functional magnetic resonance imaging (fMRI) scanner. In this procedure, conditioned responses are formed when a conditioned stimulus is paired with a mild electric shock. Skin conductance response was used as an index of the conditioned response.
- During extinction recall, functional activity in the right supramarginal gyrus was higher in the mindfulness group than in the exercise group
- For the mindfulness group, activity in the right supramarginal gyrus was significantly correlated with the total number of minutes of reported mindfulness practice at home
- In the early phase of retrieval, the mindfulness group, but not the exercise group, showed the increased functional coupling of the hippocampus to the right primary sensory cortex. This part of the sensory cortex is typically associated with the left hand, where participants had the shock electrodes placed
- Increases in hippocampal gray matter intensity following mindfulness training predicted enhanced connectivity between the hippocampus, dorsolateral prefrontal cortex and retrosplenial cortex. These changes were noted only during the early phase of recall
A Plausible Mechanism
Strengthened hippocampal circuits following mindfulness training appear to be associated with enhanced retrieval of extinguished fear memories. Hippocampal-dependent change in contextual retrieval is a plausible mechanism by which mindfulness training regulates effective response, fosters stress resilience and curtails susceptibility to anxiety.
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