Acem meditation, which was originally developed in Norway, involves adopting a "free mental attitude" similar to mindfulness meditation in allowing "any thought, memory, emotion, or sensation to emerge and pass through the awareness of the practitioner, without any volitional attempt to control the current content." A meaningless multisyllable sound is repeated to induce relaxation.
18 experienced meditators were recruited form the acem meditation community. Subjects acted as their own controls, and a meditation condition was contrasted with a quite rest condition. The results indicated that this form of meditation increased theta (4-8 Hz) and alpha (8-12 Hz) waves significantly more than relaxation. Theta activity was greater in frontal and central-temporal regions and alpha was more abundant posteriorly. The authors of the study speculated that the increased theta activity likely reflects increased awareness and attention, as well as cognitive and affective processing during meditation, whereas the increase in alpha activity likely relates to relaxation. The greater theta in frontal and temporal-central regions than in posterior regions was thought to reflect neural processing in the frontal midline (anterior cingulate cortex) and limbic areas, which have a prominent role in emotional processing. The abundance of posterior alpha waves was thought to be related to reduced cognitive processing in sensory-related areas.
Jim Lagopoulos, Jian Xu, Inge Rasmussen, Alexandra Vik, Gin S. Malhi, Carl F. Eliassen, Ingrid E. Arntsen, Jardar G. Sæther, Stig Hollup, Are Holen, Svend Davanger, and Øyvind Ellingsen. The Journal of Alternative and Complementary Medicine. November 2009, 15(11): 1187-1192. doi:10.1089/acm.2009.0113.