The Science of Meditation

Experience: Brief training (Level 4)

Finding: The participants in the goodwill (metta) meditation group showed positive changes in mood and positive evaluations of others (social connectedness) after 7 minutes of training.

Quality of Evidence: Control task

Caveats: The moderate sample size (n=93) may limit the generalization of these findings to people with different levels of meditation experience or cultural backgrounds. Moreover, the study's self-report measures for mood and explicit evaluations are subjective—possibly influenced by social desirability bias.

Source: Hutcherson, C. A., Seppala, E. M., & Gross, J. J. (2008). Loving-kindness meditation increases social connectedness. Emotion, 8(5), 720. https://psycnet.apa.org/record/2008-13989-015

Experience: Secular programs (Level 3)

Finding: 8 hours of compassion training brings increased altruism and altered neural connectivity linking a central command center of the brain (prefrontal cortex) to a reward hub associated with joy (nucleus accumbens), similar to more advanced meditators.

Quality of Evidence: In this study, the training consisted of guided audio instructions for 30 minutes each day over two weeks, providing a structured and consistent approach. The use of behavioral tasks (Redistribution Game) and neuroimaging (fMRI) adds depth to the evaluation of altruistic behavior and neural changes.

Caveats: The study lacks a baseline measure of altruistic behavior before training, which weakens claims about the impact of the training. The findings are based on a relatively small sample size (n=41) and might benefit from replication with larger and more diverse samples.

Source: Weng, H. Y., Fox, A. S., Shackman, A. J., Stodola, D. E., Caldwell, J. Z., Olson, M. C., ... & Davidson, R. J. (2013). Compassion training alters altruism and neural responses to suffering. Psychological science, 24(7), 1171-1180. https://journals.sagepub.com/doi/abs/10.1177/0956797612469537

Experience: Brief training (Level 4)

Finding: Compassion training may enhance resilience and change attitudes from empathic (feeling others’ pain with them) to compassionate (finding joy in helping them out of it). Compassion reversed participants’ negative feelings from empathy, bringing them back to baseline, and altered neural circuitry.

Quality of Evidence: The study design included a memory control group, and the participants' experiences were measured through subjective ratings of empathy, positive affect, and negative affect in response to socio-affective video tasks. The memory control group did not show the same pattern of affective and neural changes observed in the empathy and compassion training groups, serving as a control condition, although the memory training demonstrated effectiveness in improving memory performance.

Caveats: The sample consisted only of female participants, and it is unclear whether the findings can be generalized to males. The sample size of 25 was small, and 5 participants dropped out of the study.

Source: Klimecki, O. M., Leiberg, S., Ricard, M., & Singer, T. (2014). Differential pattern of functional brain plasticity after compassion and empathy training. Social cognitive and affective neuroscience, 9(6), 873-879. https://academic.oup.com/scan/article/9/6/873/1669505

Experience: Secular programs (Level 3), 3-month training

Finding: 3 months of compassion training altered oxytocin, a hormone linked to prosocial emotions and stress response regulation. Oxytocin levels decreased during stress but increased during goodwill meditation. This suggests that stressful events lost their importance in the brain, while positive emotions brought greater relevance, according to the authors. Surprisingly, goodwill meditation did not change oxytocin level responses during a stressful event.

Source: Hoehne, K., Vrtička, P., Engert, V., & Singer, T. (2022). Plasma oxytocin is modulated by mental training, but does not mediate its stress-buffering effect. Psychoneuroendocrinology, 141, 105734. https://www.sciencedirect.com/science/article/pii/S0306453022000750

Experience: Secular programs (Level 3), 12-week training

Finding: 12 weeks of metta appears to slow biological aging compared to mindfulness practice and a control group.

Source: https://www.sciencedirect.com/science/article/abs/pii/S0306453019300010

Experience: Mostly Traditional training (Level 1), Meta-analysis of 10 studies

Finding: Metta and compassion training are linked to several well-being measures, including less inflammation, anxiety, depression, stress, and negativity and increased cognitive functioning.

Source: "Effects of Kindness- and Compassion-Based Meditation on Wellbeing, Prosociality, and Cognitive Functioning in Children and Adolescents: a Systematic Review" (Mindfulness, 2023) https://link.springer.com/article/10.1007/s12671-022-01925-4

Experience: Brief training (Level 4), meditation-naive participants

Finding: In terms of cognitive performance, both groups improved in response times initially. There were no significant differences between the meditation and control groups. More meditation time correlated with greater increases in mindfulness.

Quality of Evidence: Small sample size (n=40), including a randomized control group. The study utilized a mixed-methods approach, combining behavioral tasks, self-report measures, and EEG recordings. The inclusion of various measures enhances the comprehensiveness of the investigation. The meditation group adhered well to the meditation schedule.

Caveats: The study focused on healthy adults, mainly of White ethnicity, limiting the generalizability of the findings to more diverse populations. There were dropouts in the meditation group, attributed to personal or health reasons. The nature and extent of these dropouts could potentially introduce bias, and the reasons for dropout should be explored further. Any potential variations in practice among participants are not explicitly discussed.

Source: Moore, A. W., Gruber, T., Derose, J., & Malinowski, P. (2012). Regular, brief mindfulness meditation practice improves electrophysiological markers of attentional control. Frontiers in human neuroscience, 6, 18. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3277272/

Experience: Secular programs (Level 3), 8-week training

Finding: There was little evidence of brain volume changes resulting from MBSR practice. However, there was a potential link between practice time and changes in the volume of the right amygdala, which is involved in emotional responses, [among other roles](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7566741/#:~:text=Specifically%2C some theories of amygdala,processing (Phelps et al.%2C).

Quality of Evidence: The study employed neuroimaging techniques and self-reported measures of mindfulness. Data was collected from a decent sample size (n=256). The findings should be interpreted cautiously due to limitations. Further research is needed to replicate them and understand the underlying mechanisms involved.

Caveats: While the study employed rigorous statistical methods, including correction for multiple comparisons, the lack of significant findings in brain structure changes raises questions about the sensitivity of the measures or potential null effects of the interventions. Also MBSR and HEP interventions were delivered by experienced instructors, but differences in the content and intensity of the interventions could have influenced the outcomes. This study failed to replicate prior findings.

Source: Kral, T. R., Davis, K., Korponay, C., Hirshberg, M. J., Hoel, R., Tello, L. Y., ... & Davidson, R. J. (2022). Absence of structural brain changes from mindfulness-based stress reduction: Two combined randomized controlled trials. Science Advances, 8(20), eabk3316. https://www.science.org/doi/abs/10.1126/sciadv.abk3316

Experience: Intensive practice (Level 2) & Secular programs (Level 3), 8-week training with long-term meditators

Finding: Stronger prefrontal cortex to amygdala connectivity.

Quality of Evidence: Included both short-term MBSR meditators (n=32), long-term meditators (n=30) and an active control (n=35). The study reported both significant and non-significant results, along with effect sizes and confidence intervals.

Caveats: Some participants were excluded from the analysis, which could affect the generalizability of the results.

Source: Kral, T. R., Schuyler, B. S., Mumford, J. A., Rosenkranz, M. A., Lutz, A., & Davidson, R. J. (2018). Impact of short-and long-term mindfulness meditation training on amygdala reactivity to emotional stimuli. Neuroimage, 181, 301-313. https://doi.org/10.1016/j.neuroimage.2018.07.013

Experience: Traditional training (Level 1) & Intensive practice (Level 2), ~10,000 hours lifetime

Finding: During (non-REM) sleep, the long-term meditators showed higher gamma brain wave activity in a specific brain region compared to the meditation-naive group.

Quality of Evidence: The study controlled for potential confounding factors such as age, sex, and education level.

Caveats: Although the study gives us good information about how meditation affects sleep, it has its limits. The group of people studied was relatively small (n=58), so it is uncertain whether the findings apply to everyone. More research with larger groups is needed.

Source: F. Ferrarelli et al., “Experienced Mindfulness Meditators Exhibit Higher Parietal-Occipital EEG Gamma Activity during NREM Sleep.” https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0073417

Experience: Traditional training (Level 1) & Intensive practice (Level 2), 9,000 hrs lifetime average

Finding: Stronger prefrontal cortex to amygdala connectivity.

Source: Kral, T. R., Schuyler, B. S., Mumford, J. A., Rosenkranz, M. A., Lutz, A., & Davidson, R. J. (2018). Impact of short-and long-term mindfulness meditation training on amygdala reactivity to emotional stimuli. Neuroimage, 181, 301-313. https://doi.org/10.1016/j.neuroimage.2018.07.013

Experience: Intensive practice (Level 2), 3-month retreat

Finding: Selective attention (ability to focus on one thing and avoid distraction) increased by 20%+ after retreat.

Source: Antoine Lutz et al., “Mental Training Enhances Attentional Stability..” Lutz A, Slagter HA, Rawlings NB, Francis AD, Greischar LL, Davidson RJ. Mental training enhances attentional stability: neural and behavioral evidence. J Neurosci. 2009 Oct 21;29(42):13418-27. doi: 10.1523/JNEUROSCI.1614-09.2009. PMID: 19846729; PMCID: PMC2789281. https://www.jneurosci.org/content/29/42/13418.short

Experience: Traditional training (Level 1) & Intensive practice (Level 2), average 9,675 hrs lifetime over 14 years

Finding: There was less activation of brain networks associated with self-related thinking (default mode network) during goodwill (metta) meditation by expert meditators compared to novices. This suggests a more selfless state of awareness. Also, the experts had fewer connections between different parts of their brains compared to novices while meditating, which could mean that less brain activity is required with more practice.

Quality of Evidence: 20 experienced meditators vs. 26 in the novice control group

Caveats: The sample size (n=46) was relatively small, which may affect the generalizability of the results.

Source: Garrison, K. A., Scheinost, D., Constable, R. T., & Brewer, J. A. (2014). BOLD signal and functional connectivity associated with loving kindness meditation. Brain and Behavior, 4(3), 337-347. https://onlinelibrary.wiley.com/doi/full/10.1002/brb3.219

Experience: Traditional training (Level 1) & Intensive practice (Level 2), average 10,500 hrs lifetime

Finding: Less activation of the DMN during meditation by experts (vs novices).

Quality of Evidence: Novice control group

Source: Judson Brewer et al., “Meditation Experience Is Associated with Differences in Default Mode Network Activity and Connectivity”

Experience: Traditional training (Level 1) & Intensive practice (Level 2), average ~9,000 hours

Finding: Less DMN connectivity during resting state (not meditating).

Quality of Evidence: Replication of earlier “accidental finding” in Garrison et al., 2014 study. See also: Pagnoni, “Dynamical properties of BOLD Activity from the Ventral Posteromedial Cortex Assocaited with Mediatin and Attentional Skills”; V.A. Taylor et al., “Impact of Meditation Training on the Default Mode Network during a Restful State”

Source: Aviva Berkovich-Ohana et al., “Alterations in Task-Induced Activity…”

Experience: Traditional training (Level 1) & Intensive practice (Level 2)

Finding: Meditators’ brains appeared about 7.5 years younger than nonmeditators at age 50, implying that meditation may slow neural atrophy.

Quality of Evidence: Meta-analysis of 21 neuroimaging studies, ~300 practitioners

Source: Fox et al., “Is meditation associated with altered brain structure? A systematic review and meta-analysis of morphometric neuroimaging in meditation practitioners”, https://www.sciencedirect.com/science/article/abs/pii/S0149763414000724?casa_token=5J1s5cdwvVkAAAAA:AplT5Tr45sk762aMeQ-AoE4pm2Mwn07Dtx8IOjWzUV1rHaeAZLksPoNaQfJ4cdaCx3RosNgzud4

Experience: Intensive practice (Level 2), 3-month retreat

Finding: Sustained ability to focus on one thing and avoid distraction increased by 20%+ after retreat.

Source: Katherine A. MacLean et al., “Intensive Meditation Training Improves Perceptual Discrimination and Sustained Attention”

Experience Level: Unknown

Finding: Increased pain tolerance. 2 degrees C (5.6 degrees F) higher pain threshold than non-meditators.

Caveats: It could be that those with higher pain tolerance are more likely to stick with Zen for long periods due to self-selection bias.

Source: Joshua A. Grant et al., “A Non-Elaborative Mental Stance and Decoupling of Executive and Pain-Related Cortices Predicts Low Pain Sensitivity in Zen Meditators,” Pain 152 (2011): 150-156.

Experience: Traditional training (Level 1), 3-year retreat complete = “lamas”

Finding: Less habituation to a loud noise, meaning their brains may have been perceiving a more fresh, “non-conditioned” flow of sensory data.

Quality of Evidence: Similar results were replicated on Zen meditators.

Source: Elena Antonova et al., “More Meditation, Less Habituation? The Effect of Mindfulness Practice on the Acoustic Startle Reflex”, https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0123512

Experience: Traditional training (Level 1) & Intensive practice (Level 2), mean of 13,727 hours of practice

Finding: ND correlated with a significant anti-correlation decrease between intrinsic and extrinsic networks when compared to a resting baseline condition, Suggesting a functional increase in connectivity between intrinsic and extrinsic networks. These key networks no longer seem to compete, aligning with the first-person reports.

Quality of Evidence: 22 experienced Tibetan Buddhist meditators; recommended by their teachers from different Buddhist meditation centers. Still, it is difficult to assess whether they successfully enter these subtle states.

Caveats: Compared nondual to non-meditative fixation and FA; but the fixation could be mistaken for FA, even though instructed to allow the mind to wander

Source: Josipovic, 2012, anti-correlated networks

Experience Level: Unknown

Finding: Enhances high-amplitude gamma brainwave activity. High-frequency gamma waves (25-42 Hz) correlate with states of heightened awareness and bliss. Long-term meditators have been shown to have more gamma wave activity both before and during meditation. 700 - 800% increase in “empathy circuitry” during meditation.

Source: https://www.pnas.org/doi/10.1073/pnas.0407401101