Posted 04.17.2018 | by AMRA

Previous learning sometimes interferes with our ability to learn new things. For example, when we memorize one poem and then another, we may mistakenly include words from the first poem when reciting the second. This problem is called proactive interference (PI). People may be able to reduce PI by focusing on the present while screening out competing thoughts and memories—in other words, by mindfulness.

Previous research suggests that reduced PI depends on activation of a brain structure known as the hippocampus. The hippocampus plays an important role in learning and memory, and helps us distinguish old learning from new. Prior research shows that mindfulness training can increase the size of the hippocampus. Greenberg et al. [Brain Imaging and Behavior] investigated whether mindfulness training reduces PI, and whether that reduction is associated with increases in hippocampal size.

The researchers randomly assigned 79 participants (70% female; average age = 27 years; 65% Caucasian) to a 4-week mindfulness-training program or a 4-week creative writing program. Of those, 67 participants were scanned using magnetic resonance imaging (MRI) before and after training to assess hippocampal volume.

Both the mindfulness and creative writing programs were offered in four 1-hour group sessions using a web-based technology that enabled participants to see and communicate with instructors and fellow participants. The mindfulness program offered training in focused-attention and open monitoring meditation. Participants were asked to practice learned mindfulness skills on their own for 30 minutes five times a week. The creative writing participants wrote short essays in response to photos or texts, and were asked to write on their own for 30 minutes five times a week.

PI was assessed before and after training by having participants memorize sets of 6 letters shown briefly on a computer screen. They were then shown a single letter and asked if it had been in the set of 6 letters just seen. This process was repeated using 144 six-letter sets. Each new set contained 3 letters seen in the previous trial together with 3 novel letters. Researchers measured errors in identifying whether the singly presented letters were included in the most recent set of six.

Mindfulness trainees showed significantly lower PI error rates after training than the writing group, after controlling for differences in pre-training error rates (partial η2=.08). Mindfulness trainees’ PI error rates decreased from 4.9 to 3.0%, while creative writing group error rates increased from 1.7 to 7.1%. Reduced PI rates were not correlated with the extent of home practice outside of class.

There was no significant difference between groups with respect to hippocampal volume change after the training period. However, within the mindfulness group only, increases in left hippocampal volume were significantly correlated with decreases in PI scores (r=.43).

The study shows that mindfulness training reduces the interference effect of previous learning on current learning. For mindfulness trainees, this reduction is associated with increased left hippocampal size. This study is important because it demonstrates a relationship between changes in hippocampal size after mindfulness-training and enhanced attention and learning.

The brevity of the study’s mindfulness training may have limited its ability to detect significant hippocampal change as compared to a control condition. Previous studies that demonstrated significant hippocampal change used an 8-week training paradigm.


Greenberg, J., Romero, V. L., Elkin-Frankston, S., Bezdek, M. A., Schumacher, E. H., & Lazar, S. W. (2018). Reduced interference in working memory following mindfulness training is associated with increases in hippocampal volume. Brain Imaging and Behavior.

[Link to abstract]