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).