Why do we chant OM?

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Sound, breath and manomaya kosha seen in the light of neurophysiology.

Mantra recitation and sound pranayama are among the oldest methods of yoga for regulating the mind. Bhramari pranayama, performed with a long, humming exhalation, and the recitation of OM are described in the classical texts as techniques that calm the mind and direct attention inward. In recent decades, a number of these effects have been studied with modern methods: EEG, fMRI, and measurements of the autonomic nervous system. This text reviews the yogic understanding and the available evidence.

The yogic model: manomaya kosha

The Taittiriya Upanishad describes man as having five sheaths (pancha kosha): annamaya (the physical body), pranamaya (energy and breath), manomaya (mind and emotions), vijnanamaya (intellect and judgment) and anandamaya (bliss).

Manomaya kosha includes thoughts, sensory impressions, emotional reactions and learned patterns (samskara). In the model, the finer layers are influenced through the coarser ones: breathing (pranamaya) forms a bridge between body and mind. This corresponds to a central insight in modern psychophysiology: the mind can rarely be regulated directly through thinking, but can be influenced indirectly via respiration and the autonomic nervous system.

Prolonged exhalation and autonomic regulation

During Bhramari and OM recitation, the exhalation is significantly prolonged and the respiratory rate typically drops to around 5–6 breaths per minute. This range is often called the resonant frequency, where breathing, heart rate, and blood pressure regulation are synchronized.

Bernardi et al. (2001, BMJ ) showed that recitation of both yogic mantras and rosary prayer decreased respiration to about 6 per minute and increased baroreflex sensitivity and heart rate variability (HRV). High HRV is a recognized measure of parasympathetic activity and the nervous system's ability to regulate stress. Studies of bhramari have also found acute decreases in heart rate and blood pressure.

Physiologically, the explanation is that exhalation is linked to parasympathetic, vagal activity. When exhalation is prolonged, the balance in the autonomic nervous system shifts from sympathetic activation towards rest and recovery.

Vibration and the vagus nerve

Kalyani et al. (2011, International Journal of Yoga) conducted a pilot fMRI study to examine brain activity during the recitation of OM compared to a control sound (“ssss”) that has the same exhalation length but does not vibrate. During OM, deactivation of limbic and paralimbic areas was observed, including the amygdala, hippocampus, anterior cingulate gyrus, orbitofrontal cortex, and thalamus. The control sound did not show the same pattern.

These areas are involved in the processing of fear, stress, and emotional reactivity. The pattern is similar to that described for electrical vagus nerve stimulation, an established treatment for treatment-resistant depression and epilepsy. The authors suggest that the vibration around the ear stimulates the auricular branch of the vagus nerve. The hypothesis is plausible, but not yet confirmed.

The point is that the effect cannot be explained by breathing alone. The vibrating sound itself, especially the closed nasal consonant M, seems to play an independent role.

Brain oscillations

EEG measures the brain's electrical rhythms:

Ribbon	Frequency	Typical condition
Delta	0.5-4Hz	Deep sleep
Theta	4-8Hz	Deep relaxation, meditation
Alpha	8-12Hz	Relaxed wakefulness
Beta	13-30Hz	Active thinking, concentration, stress
Gamma	> 30Hz	Integrated attention and perception

Meditation and slow breathing are generally associated with increased alpha and theta activity. Vialatte et al. (2009, Progress in Neuro-Psychopharmacology & Biological Psychiatry) also found short-term, strong bursts of gamma activity during bhramari in experienced practitioners. Gamma oscillations have previously been described in long-term meditators and are associated with increased attention and neural synchronization.

The results indicate that bhramari not only dampens brain activity, but can induce a state of simultaneous calm and heightened awareness, which corresponds well to the yogic description of sattva. However, it should be emphasized that the study is small and that gamma measurements by EEG can be affected by muscle activity.

Nitric oxide in the sinuses

Weitzberg and Lundberg (2002, American Journal of Respiratory and Critical Care Medicine) measured that humming increased the concentration of nitric oxide (NO) in the nose approximately 15-fold compared to quiet exhalation. The vibration increases air exchange between the sinuses and nasal cavity, where NO is formed.

NO has vasodilating and antibacterial and antiviral properties. The finding is primarily relevant to the respiratory tract, but shows that sound has measurable physiological effects in addition to neurological ones.

Why exactly OM?

In the classical analysis (Mandukya Upanishad), OM consists of three sounds, AUM, followed by silence. The three sounds correspond to the waking, dreaming and sleeping states, while the silence represents turiya, the pure consciousness behind them.

Physiologically, OM combines the three elements described above: a long exhalation, an open vowel that activates the vocal cords and chest, and a final M that creates resonance in the skull and sinuses. It is precisely this combination that distinguished OM from the control sound in the fMRI study.

Limitations

The research is promising, but has clear limitations:

• Most studies are small, often with 10–20 participants.

• Several are pilot studies without randomization or blinding.

• Long-term effects have been sparsely studied.

• The mechanism via the vagus nerve is a hypothesis, not documented.

The conclusion should therefore be cautious: the evidence indicates that bhramari and OM recitation acutely affect the autonomic nervous system and the activity in the emotional centers of the brain towards calmness and regulation.

Note: In the language of yoga, sound and breath energize the manomaya kosha. In the language of neurophysiology, they increase vagal activity, lower the respiratory rate towards resonance, dampen activity in the amygdala and limbic structures, and change the oscillation patterns of the brain. The two descriptions are not contradictory. They describe the same phenomenon from two sides: from within as experience and from without as measurement.