A meta-analysis of 163 studies on meditation in nonclinical adults found medium average effects (r = .28) on psychological variables, not explainable by relaxation or cognitive restructuring alone. Effects were strongest for emotionality and relationships (medium to large), medium for attention, and small to medium for cognitive measures. Results varied by meditation type (transcendental, mindfulness, other). Meditation experience only partially predicted long-term impact. Most of 595 initial studies were excluded due to methodological problems, and many lacked theoretical grounding. The authors call for more precise theories and measurement tools to understand how meditation works.
Altered states of consciousness (ASC) can occur spontaneously, be evoked by physical or physiological stimulation, induced by psychological means, or caused by diseases. Psychological and neurobiological approaches reveal four dimensions characterizing ASC: activation, awareness span, self-awareness, and sensory dynamics. Neurophysiologically, different states of consciousness arise from compromised brain structure, transient changes in brain dynamics (disconnectivity), and neurochemical and metabolic processes. Environmental stimuli, mental practices, and self-control techniques can also temporarily alter brain functioning and conscious experience.