- Participants who underwent mindfulness training exhibited a significantly lower error rate on a task measuring proactive interference when compared with an active control group
- These improvements were significantly associated with increased volume of the left hippocampus
- Mindfulness training may be beneficial in a range of conditions characterized by impairment of working memory and reduced hippocampal volume, including normal aging
Mindfulness training teaches people to focus on the present moment and minimize distraction from competing thoughts and memories. It is known to improve working memory, as well as to increase hippocampal density. However, until recently, the link between those two effects had never been studied.
A team of Mass General researchers led by Jonathan Greenberg, PhD, a postdoctoral research fellow, and Sara W. Lazar, PhD, an associate researcher in the Department of Psychiatry, are the first to show that mindfulness training reduces proactive interference in working memory and that such reductions are associated with increased hippocampal volume. Their report appears in Brain Imaging and Behavior.
Proactive interference in working memory occurs when old information prevents the recall of newer information. For example, the memory of a friend’s former telephone number may make it harder to remember the new one. Overcoming proactive interference is essential to high-level cognitive functions such as learning, reasoning and problem-solving. The hippocampus plays a key role in making such distinctions, in both long-term and working memory.
Investigating the Potential of Mindfulness
That fact led the researchers to suspect that people who take mindfulness training might exhibit greater improvements in proactive interference than individuals who engage in some similar experience. To investigate, they randomly assigned 79 healthy individuals (mean age 27 years) to take mindfulness training (n=50) or a class in creative writing (control group, n=29). Both programs consisted of four weekly, hour-long web-based sessions.
Before and after the programs, all participants completed the Recent Probes Task, a measure of proactive interference in working memory using memorization tasks. Prior to the classes, the group assigned to mindfulness training exhibited significantly higher error rates on this task compared with the control group. After the programs ended, the mindfulness group showed greater improvement in error rates than the control group did.
The first 67 participants recruited underwent MRI before and after the training programs (39 in the mindfulness group, 28 in the control group). In that subset of participants, there was no difference between the mindfulness group and the control group in hippocampal volume, either before or after training.
On regression analysis, however, the volume increase in the left hippocampus was significantly associated with improvements in the proactive interference error rate and only in the mindfulness group.
Why Mindfulness Training Is Effective
The researchers note that at present, mindfulness training is being used primarily to treat distress and mood-related symptoms. The study findings suggest that mindfulness training is useful to treat these conditions in part because it reduces proactive interference. Mindfulness encourages the brain to pay attention to the present moment while minimizing interference from past events.
The study team also concludes that mindfulness training may be beneficial in other conditions characterized by impairment of working memory and reduced hippocampal volume, such as aging, post-traumatic stress disorder and childhood mistreatment and abuse.
Learn more about the Lazar Lab for Meditation Research
Learn more about the Department of Psychiatry