We shall attempt to review the progress in neurobiology in the recent years. In the following article an attempt is made to throw light on this new and fascinating subject. The terms used are technical, but, as far as possible, an attempt is made to simplify the description. This attempt to explain the Neurophysiology is purely hypothetical.

Meditation and Changes in Neurophysiology:

In an attempt to enter into a state of altered consciousness, the Yogi try to concentrate, contemplate and meditate on a single idea or a form related with divine or spiritual. The brain may perceive this as psychological stimuli. One of the ways to control physiological reactions to psychological events is meditation, Yoga, Zen Buddhism etc. A few scientists had taken Transcendental Meditation (TM) as the uniform technique, and had based their observations on the study of the subjects engaged in this form of meditation. In summing up the results they confirmed that the effect of meditation was a "wakeful, hypo-metabolic state". They concluded that the pattern of changes generated was mediated through the control of autonomic nervous system in the brain (limbic system) and spinal cord.

They have found that:

1. Yogis could slow both heartbeat and rate of respiration,

2. Yogis could slow the rate of metabolism as confirmed by decreased oxygen consumption and carbon-di-oxide output.

3. EEG in Yogis showed changes of calmness in the form of alpha rhythm activity during both eyes closed and open recording.

4. Their skin resistance to electric stimulation was increased (indicating increased tolerance to external stimuli).

In the early history of mankind the 'defense-alarm' reaction to psychological and physical stress was in the form of "fright, flight, and fight" mediated through the over-secretion of neurotransmitters and neuro-modulators dopamine and adrenaline by stimulation of sympathetic nervous system. We reflexively become panicky, our blood pressure increases, and stress and anxiety are the end results if we allow our natural age-old sympathetic reactions come to surface. We try to run away or fight the situation. But today these 'defense-alarm' reactions have no place in our lives. Rather, they should be replaced by more calm and serene reactions of equanimity and peace. The need is to just 'face the brute, and it will go away'. Such desirable reactions of contemplation and peaceful attitude are generated by Yoga and meditation.

Here the usually dominant action mode is suppressed in favor of receptive mode that brings peace and bliss even in the disturbing circumstances. It is thought that the left half of the brain is dominant in right-handed people, while right half is said to be non-dominant. However, the transfer of functions from one half to another can occur with learning and practice. This has been shown to occur in persons who had neurological damage to one side of the brain. Increasing knowledge of neurobiology and brain imaging techniques is further reinforcing the role of plasticity after neuronal damage with the stimuli from practice, intense concentration and experiences.

EEG Studies on Yogis and The Zen Meditations 

Yogis practicing Raja-Yoga claim that during the state of Samadhi they are oblivious to the internal and external stimuli, and they enjoy a calm ecstasy during that state. A study was undertaken to record the electrical activity of their brain during this state by means of a regular and useful test known as electroencephalography- EEG. Physiological and experimental studies have demonstrated that the basis of the conscious state of the brain, among other things, is activation of the reticular system of the brain stem through internal and external stimuli. These stimuli bring about various changes during sleep and wakeful states of the organism that can be studied by EEG.

The study was carried out on four subjects during the state of concentration and meditation. Effects of external stimuli, like a gong, strong light, thermal simulation, and vibrations were studied. The results were compiled and analyzed. It was observed that two Yogis could keep their hands immersed in very cold water for 50 minutes or so (raised pain threshold). During the state of meditation, all of them showed persistent alpha activity with increased amplitude wave pattern, both during eyes closed and open recording. It was observed that these alpha activities could not be blocked by various sensory stimuli during meditation. It was also observed that those who had well-marked alpha activity in their normal resting records showed greater aptitude and zeal for maintaining the practice of Yoga. Similar observations and results were obtained when EEGs were recorded in persons adept in Zen Meditative technique.

Discussion and Conclusion 

Neurotransmitters and Neuro-modulators: These are chemical substances released at the neuronal junction (Synapses). They act by altering the electrical membrane potential by opening up channels that permit diffusion of Sodium, Potassium, and Calcium ions in and out of the nerve cell. They not only transmit the message from one cell to another, but also selectively facilitate some information while inhibiting the other. Moreover, the action of Calcium ions permits transfer of electrical events into molecular changes that can alter functions of the nerve cells permanently, i.e. change cellular function to subserve a memory or learning response.

Neuro-modulators affect the neurotransmitters by influencing neuronal plasticity, growth, or differentiation. Different types of receptors as present in different regions of brain can account for the complex multiple effects of medications, meditation, concentration, and contemplation. This may be effected through actions of specific type of neurotransmitter and neuro-receptor.

For example, a sub-type of glutamate receptor appears to mediate the function of brain plasticity, a process considered important in learning and memory. Acetylcholine helps in memory, motivation, perception and cognition. It is also involved in attention and arousal functions of ascending reticular system. Decrease in the levels of this neuro-modulator leads to loss of memory, senile dementia-Alzheimer's disease. 

Excess of Serotonin, another important neuro-modulator, leads to hallucinations, as seen in LSD consumption, which causes increase in Serotonin level. This discovery brought into focus the correlation between behavior and variation in brain Serotonin content. Selective depletion of Serotonin, in animals, causes prolonged wakefulness. It also plays important role in circadian rhythm and sleep cycle. 

Other neurotransmitters and modulators like nor-epinephrine cause changes in mood-excess leading to elation, and deficiency causing nervous depression. It also controls food intake, regulates body temperature, and hormonal secretions. Excess of dopamine level is responsible for schizophrenia and psychosis. Nerve growth factor is a hormone like peptide that is responsible for the growth and maintenance of various brain structures.

The Plausible Hypothesis

To explain the altered state of consciousness brought about by intense and prolonged mediation a Plausible Hypothesis may be constructed as follows:

The evolutionary process adds higher centers to the primitive nervous system. These higher centers have inhibitory influence over the lower centers. Thus, the brain stem is controlled by limbic system and limbic system in turn is controlled by the higher new brain center - neo-cortex. The neuro-modulators with their influence on various neurotransmitters effectively bring about this inhibitory modification in inter-relation amongst various brain centers (hierarchy). For instance, involuntary movements are suppressed by basal ganglia through the action of dopamine and acetylcholine synergy. Any imbalance in these neuro-modulators causes involuntary movements like chorea and tremors. Similarly, loss of cortical control over the motor neurons of spinal cord leads to exaggerated muscle and tendon jerks due loss of inhibitory control of the higher cortex.

Neo-cortex keeps all the involuntary movements, hyper-reflexivity, rage, aggression, and similar animal tendencies under check so that it can effectively pursue its own highly developed activities of logic, memory, reason, language, calculations, judgment, and concepts, etc. Conscious, willful, imaginative functions are therefore, normal state of awareness of the human beings.

When meditation acts as a constant repetitive stimulus, certain qualitative and quantitative permanent changes develop in the nervous system. The neurotransmitters and neuro-modulators may stimulate growth of dormant or latent neurons to develop a center (or centers), which on the evolutionary ladder is/are still higher than the present day cerebral cortex. The brain may develop new connections and plasticity resulting in the capacity to think, to rationalize, and react in a different way to the sensory input than what is expected by present day physiologists. For want of name, we may label it as 'God Module'. This higher center will exert inhibitory control over the present day neo-cortex, and thereby, over the mind as a whole (consciousness, reasoning, conceptual thinking, willing, feeling, and doing, etc.)! The consciousness and all mental activities will hence be suppressed. The person will reach a state beyond mind itself-transcendental awareness! 

"The spiritual ascent is from the least evolved state of consciousness to near perfect state, after which the mind itself will cease to be, and there will remain only non-dual experience."