Cerebral blood flow during meditative prayer: preliminary findings and methodological issues.

Meditative practices typically require several coordinated cognitive activities. This study measured changes in cerebral blood flow during "verbal" based meditation by Franciscan nuns involving the internal repetition of a particular phrase. These results are compared with those we previously described in eight Buddhist meditators who use a type of "visualization" technique. Three experienced practitioners of verbal meditation were injected via i.v. at rest with 260 MBq of Tc-99m HMPAO and scanned 30 min. later on a triple head SPECT camera for 45 min. Following the baseline scan, subjects meditated for approximately 40 min. at which time they were injected with 925 MBq of HMPAO while they continued to meditate for 10 min. more (total of 50 min. of meditation). The injection during meditation was designed not to disturb practice. Subjects were scanned 20 min. later for 30 min. Counts were obtained for regions of interest for major brain structures and normalized to whole-brain blood flow. Compared to baseline, mean verbal meditation scans showed increased blood flow in the prefrontal cortex (7.1%), inferior parietal lobes (6.8%), and inferior frontal lobes (9.0%). There was a strong inverse correlation between the blood flow, change in the prefrontal cortex and in the ipsilateral superior parietal lobe (p<.01). This study on a limited number of subjects demonstrated the feasibility of studying different types of meditation with neuroimaging techniques, suggested that several coordinated cognitive processes occur during meditation, and also raised important methodological issues.