Tammi Kral

Who they are

Kral is a neuroscientist whose 2022 paper came from the laboratory of Richard Davidson. The paper lists ten authors: Kral, Kaley Davis, Cole Korponay, Matthew Hirshberg, Rachel Hoel, Lawrence Tello, Robin Goldman, Melissa Rosenkranz, Antoine Lutz and Davidson.

The vault's earlier notes gave her first name as Tim. The paper itself gives it as Tammi, and this site uses that. The correction matters beyond tidiness, because a paper that is cited under the wrong first author is harder to find, and this one is the paper that most directly tests a widely cited structural claim.

Key papers

Kral, T. R. A., Davis, K., Korponay, C., Hirshberg, M. J., Hoel, R., Tello, L. Y., Goldman, R. I., Rosenkranz, M. A., Lutz, A., & Davidson, R. J. (2022). "Absence of structural brain changes from mindfulness-based stress reduction: Two combined randomized controlled trials." Science Advances, 8(20), eabk3316.

The paper pools two three-arm randomised trials with 218 meditation-naive adults. After a baseline scan, participants were assigned to a waitlist control, an eight-week mindfulness-based stress reduction programme or a matched active control. Structural MRI measured grey-matter volume, grey-matter density and cortical thickness before and after the intervention. The authors found no evidence that the programme produced structural changes compared with either control group, across the whole brain or in regions of interest drawn from earlier mindfulness research. They report that they did not replicate the earlier findings.

The Center for Healthy Minds summary of the work describes the active control as the Health Enhancement Program, which combines exercise, music therapy and nutrition education without mindfulness training. It also notes that participants in both the mindfulness and the active-control programmes reported more mindfulness than the waitlist group, which the authors suggest may reflect general wellness effects and not anything specific to meditation.

Key ideas

An active control, not only a waitlist. A waitlist group tells you what happens with no programme. An active control tells you what happens with a programme of similar time and attention but different content. The Kral design includes both, which lets a structural change be attributed to mindfulness training specifically or not at all. The result is that nothing separated the mindfulness group from either comparison.

Scale and randomisation. The earlier study of this question, by Britta Hölzel and colleagues in 2011, scanned 16 participants in the course group and compared them with 17 people on a waiting list. Kral and colleagues pooled 218 participants across two randomised trials. A larger, randomised design is better placed to separate a real structural effect from noise, and in this case it did not find one.

What the authors say about the limits. They note that the sample was healthy and not seeking help, which may leave less room for change than in groups recruited for stress. They suggest that structural change might appear only with much longer training or training focused on a single practice, and that mindfulness engages many interconnected regions that may change to different degrees in different people, which can make group-level change hard to detect. They call for replication.

The scope of the result. The paper concerns brain structure alone, after a short course, in novices. It does not address other outcomes of the course and it does not address long-term practitioners, who were not studied. On this site the paper is used for one purpose: to show that a structural claim attached to a short programme did not hold when tested with randomisation.

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