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Today, there is a paradigm shift around the concepts of health, illness, and treatment options. We are living in a time where medical physicians largely rely on technology and drugs to treat illness and disease. Yet in the midst of the best health care system that western medicine has to offer, millions of people are seeking alternative health care (Barnes,2004 ). In the recent past, efficacy and therapeutic effects of yoga have been reported in various medical journals using latest technology, suggesting that yoga has scientific basis. Moreover, millions of people are exploring and paying for such complementary treatment primarily out of their own pocket, which again emphasises and acknowledges the positive and healing effect of yoga.

In the continuing endeavour to unravel the neurobiological mysteries of yoga, latest imaging technologies are constantly being used, like functional magnetic resonance imaging (fMRI) (Baerentsen et al, 2001), positron emission tomography (PET) of regional cerebral metabolic rate & regional cerebral blood flow, radio-ligand binding to receptors of neurotransmitters (Kjaer,2002, Roggia,2001), diffusion tensor imaging (DTI), magneto encephalography, conventional electroencephalography (EEG), quantitative electroencephalography (qEEG) and event-related potentials (ERP).

Especially, qEEG is a non-invasive tool that is capable of assessing quantitatively the resting and evoked activity of the brain, having a high sensitivity and a temporal resolution superior to those of any other imaging method.

In the past 20 years, research in EEG has made significant contributions to the understanding of brain-electrophysiology. Recently, digital electroencephalography has come into widespread use and has become an established alternative to conventional EEG (Nuwer, 1997). EEG records the action potentials of electrical energy generated by cortical neurons, by a non-invasive method through electrodes placed on the scalp. An extension to this is the electrocorticograms, an invasive procedure that records electrical potentials over the human cortex.

The EEG rhythms recorded on the scalp are the result of the summation effect of many excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs) produced in the pyramidal layer of the cerebral cortex. In humans, the thalamus is thought to be the main site of origin of EEG activities (alpha and beta bands). Thalamic oscillations activate the firing of the cortical neurons. The depolarisation (mainly in layer IV) creates a dipole with negativity at layer IV and positivity at more superficial layers. The scalp electrodes will detect a small but perceptible far-field potential that represents the summed potential fluctuations. Scalp electrodes cannot detect charges outside six square centimetres of the cortical surface area, and the effective recording depth is several millimetres (Thakor and Shanbao, 2004).

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