Even people meditating for the first time will register a decrease in beta waves, a sign that the cortex is not processing information as actively as usual. After their first 20-minute session, patients show a marked decrease in beta-wave activity, shown in bright colors, top.
BEFORE meditation --Frontal lobe --Parietal lobe --Occipital lobe
AFTER meditation --Frontal lobe --Parietal lobe --Occipital lobe
Inside the Meditating Brain
Frontal lobe This is the most highly evolved part of the brain, responsible for reasoning, planning, emotions and self-conscious awareness. During meditation, the frontal cortex tends to go offline.
Parietal lobe This part of the brain processes sensory information about the surrounding world, orienting you in time and space. During meditation, activity in the parietal lobe slows down.
Thalamus The gatekeeper for the senses, this organ focuses your attention by funneling some sensory data deeper into the brain and stopping other signals in their tracks. Meditation reduces the flow of incoming information to a trickle.
Reticular formation As the brain's sentry, this structure receives incoming stimuli and puts the brain on alert, ready to respond. Meditating dials back the arousal signal.
After training in meditation for eight weeks, subjects show a pronounced change in brain-wave patterns, shifting from the alpha waves of aroused, conscious thought to the theta waves that dominate the brain during periods of deep relaxation
Relaxation increases... Power of theta waves as a percentage of total EEG power --Meditation group --Control group --Sessions
...conscious thought decreases Power of alpha waves as a percentage of total EEG power --Meditation group --Control group --Sessions
Source: Dr. Gregg Jacobs, Harvard Medical School, author of The Ancestral Mind.