The authors conclude that their study provides evidence that meditation practice of the type studied results in increases in the level of gamma activity during meditation and that baseline levels are higher for long-term practitioners before and after meditating. Their study is consistent with the idea that attention and affective processes, which gamma band activity reflects, can be trained. Their study demonstrates that this type of objectless meditation has a different profile than concentration meditation characterized by increases in slow alpha or theta during meditation (Shapiro, 1980).
Lutz, A., Greischar, L. L., Rawlings, N. B., Ricard, M., & Davidson, R. J. (2004). Long-term meditators self-induce high-amplitude gamma synchrony during mental practice. Proceedings of the National Academy of Sciences of the United States of America, 101(46), 16369-16373.
Shapiro Jr, D. H. (1980). Meditation: Self-regulation strategy and altered state of consciousness. Aldine.