The brain activity of nine experienced Isha Yoga practitioners was measured before and after the Shambhavi Mahamudra Kriya (SMK) practice. Electroencephalography (EEG) was used to monitor the brain using non-invasive electrodes placed at 19 different locations along the scalp. Measured brain activity was sorted into four different frequency ranges: Beta, Alpha, Theta and Delta. Beta frequencies (high range), generally associated with mental tension and anxiety, showed marked decrease at specific locations after the practice. Delta and theta frequencies (low range), indicative of deep relaxation and meditativeness showed substantial increases throughout the brain. Alpha (mid range), also asociated with relaxation showed minor decreases in only select regions and maximum increases in certain other regions. High overall prevalence of alpha frequencies before and after practice in these experienced SMK practitioners suggested high levels of general relaxation.

Table summarizing the effect of Shambhavi Mahamudra Kriya practice on brain waves.

Delta and theta are considered "slow" waves due to their low frequencies. The ratio [(Delta+theta)/alpha] is used as a method to assess how many slow waves are there compared to mid-range waves (alpha). Here, a significant increase in this ratio was observed, indicating greater relaxation and mental consciousness after the practice.

Coherence is a mathematically calculated value that can range from 0 (low coherence) to 1 (high) based on similarities in the wave patterns between the two hemispheres (also known as inter-hemispheric coherence). Coherence significantly increased after the practice at most locations, suggesting improved functional connectivity between the two hemispheres of the brain; this is also a sign of enhanced cognitive ability, flexibility and emotional stability.

Shambhavi EEG paper