REVISITING THE NEUROPHYSIOLOGIC MODEL OF MEDITATION

DEEPAK K.K., M.D., Ph.D., M.N.A.M.S.
Professor of Physiology, All India Institute of Medical Sciences, New Delhi, India

Meditation is a complex psycho-physiological behavior which presents an enigma for physiologists. It utilizes the existing brain circuits to generate a unique perceptual-sensory experience. This results in varying degree of somato-visceromotor relaxation. A psycho-physiological analysis suggests involvement of elements of focused but non-analytic attention. A physiological analysis of the components of this psycho-physiologic behavior vis-a-vis various neurophysiological evidences implicates activation and deactivation of several brain structures involved in the induction of meditation. Physiologically speaking, the mechanisms appear to be involved are, 'efferent attenuation', 'sensory attenuation' and 'cognitive restructuring'. Considering the overt and covert behavioral manifestations and evidences of involvement of neural structures, a neurophysiological model was generated. According to this model the decision process to initiate and engage in the meditative practice appears to be mediated at the level of prefrontal cortex. Under the influence of prefrontal cortex the other association cortices namely posterior parietal cortex and temporal cortex, disengages themselves from active processing and slips into in an active but disengaged state. The thalamus by using its natural rhythm drives disengaged association cortices. Once initiated, such activation becomes self sustained. The state of meditation is maintained until interrupted either by re-engagement of association cortices in information processing or by disturbing the rhythm of the thalami. The association cortices may be interrupted by either internal thought perturbations or by intruding external sensory inputs. The thalamus has obligatory function of gating sensory input and then it directs the out flow to cortices. Thus, on receiving a sensory barrage, the thalamus may switch to different processing mode depending on the physiological needs of the input. This particular neurophysiological model with some modification may provide explanation for depth related phenomena of meditation and different variants of meditation. The prolonged practice of meditation results in generation of newer pattern of psycho-physiologic expressions, possibly through the process of neural plasticity. The continual practice may be reinforcing certain neural circuits and inhibiting unused ones. The same principle is exploited by neuro-feedback for producing desired benefits in cases on disease. Thus not only this model unravels neural (attention, learning) and psychologic (perceptual changes) mechanisms in physiology but also useful in providing insight into the mechanisms involved in certain diseases like epilepsy, anxiety and depression.

YOGA AS THERAPY IN MENTAL DISORDERS

PROF. GANGADHAR B.N. and THIRTHAHALLI J.
Department of Psychiatry, NIMHANS, Bangalore, India

Role of Yoga in promoting mental health is nearly incontrovertible. The use of Yoga in treating mental disorders is hence an important issue. Depressive disorder is common among the mental disorders. Treatment of depression is a challenge on several counts. The medications against depression are associated with side effects and even the risk of self-poisoning. Response rates to antidepressant drug treatments are not totally encouraging. Search for alternative forms of treatment is on continuously. Yoga offers promise. Sudarshana Kriya Yoga (SKY) is a form of controlled respiration at different rates and styles. Developed by Sri Sri Ravishankar Guruji of the art-of-living foundation, SKY has gained wide acceptance as well as popularity. Initial studies in depressive disorder not only demonstrated SKY's antidepressant effects but also the potency of SKY in comparison to drugs. SKY had pronounced effects on prolactin secretion. On regular practice SKY reduced plasma cortisol, a hormone associated with stress. SKY produced significant 'improvement' in the amplitude of a cognitive event related potential (P300). Significant antidepressant effects of SKY and similar neuroendocrine effects were demonstrated in acutely detoxified patients of alcohol dependence. Other Yogasanas were tried as adjuvant to ongoing neuroleptic therapy in schizophrenia patients. This was a comparison study with a control exercise group. Yogasanas were more effective than exercise when added to ongoing neuroleptics. The results encourage routine use of Yogasana as an add-on treatment in schizophrenia. Yogasana carried little adverse effects and are more socially acceptable. More studies to reinforce evidence-base are recommended to develop such a strategy.