Shirley Telles, Catherine Joseph, S. Venkatesh and T. Desiraju
Department of Neurophysiology, National Institute of Mental Health
and Neuro Sciences, Bangalore (India)
(Accepted 24 September 1992)
Yogic practices were devised in ancient times to perhaps aid in realising the capability of highest possible functional harmony in body and mind. Pranayamic exercises are among the important yogic practices (Vivekananda, 1973). There are several varieties of pranayamas, some of them (ujjayi, bhastrika variants) require a conscious regulation of the breathing rhythm, maintaining specified ratios of time durations of inspiratory and expiratory phases, as well as timed breath holding in the post-inspiration or post-expiration period, and also holding attention in either imagining the flow of energy along spinal column collaterally with breathing rhythm (Vivekananda, 1973), or in experiencing the sensation of inhaled air touching and passing through the nasal passage (Behanan, 1937), or on concentrating on certain other parts of the body. Since these types of pranayamic practices involve considerable exercising of conscious control processes with precision, a study of evoked potentials in them may reveal some clues of the brain mechanisms underlying such a conscious exercise. Furthermore, since the respiratory rhythm provides an observable indication of the subject being engrossed in the conscious control process, the experimenter can be sure of the subject engaged in the yogic practice during the data acquisition, unlike in subjects doing meditation when no such external indicator will be available to know whether the subject is smoothly continuing in the meditative exercise. For these reasons, we proposed to examine the ujjayi and bhastrika types of pranayama subjects to assess alterations in middle latency auditory-evoked potentials (AEP-MLRs). The AEP-MLRs were chosen to begin with, instead somatosensory MLRs to avoid compounding with any sensory-motor potentials produced during the controlled respiratory movements, and to reveal changes of a generalised nature that might be induced by the consciously attentive yogic exercise in the processing of information in a modality other than the somatosensory. The MLRs have been chosen for the study with the premise that conscious processes actively involve several cortical mechanisms and also that corticofugal control processes may exert significant alterations in the processing of information at the brainstem and thalamic levels (Desiraju. 1979, 1984; Steriade and Llinas, 1988; Pribram and McGuiness, 1993, in press).