Description of an EEG pattern evoked in central--parietal areas by the Hathayogic exercise Agnisara

Agnisara is a Hathayogic exercise consisting essentially in alternate, forceful retractions and protrusions of the abdominal wall, performed along a 20-30 s period of apnoea. In the course of series of Agnisars spindle bursts of a "wicket" EEG wave pattern developed over the para-Rolandic areas of the cerebral cortex, at frequencies around 12-13 Hz, with waxing and waning amplitudes in the range of 50 to 100 microV. These spindle-bursts, which occurred preferably during the phase of retraction of the abdominal wall, were named "Xi" rhythm (after the Greek letter X). It is the same as the one that regularly accompanies the performance on various other Hathayogic exercises. Xi spindles were recorded in linked earlobe reference derivations from areas located bilaterally midway between F-C, C-P, and P-O standard electrode positions of the 10-20 system. This EEG pattern would be considered as the expression of the central excitation, produced by the exercise's long-lasting and repeated stimulation of visceral, and somatic receptors. Thus, this activation affects mainly cortical structures with somato-visceral representation.