Mechanistic Insights from Neurophysiological 
Studies of OM Chanting,Pranayama and Yoga 
Nidra on Sleep Quality

We read with great interest the randomised controlled trial by Akshita et al. ¹ which evaluated a 24-week, home-based pranayama and Yoga Nidra programme in elderly hypertensive individuals. This groundbreaking study represents the first home-based, mobile-guided yoga intervention specifically designed for hypertension management and sleep quality improvement in elderly populations. The intervention modules, structured according to protocols from the Ministry of Ayush, India and Central Council for Research in Yoga and Naturopathy publications on naturopathic and yogic management of hypertension, demonstrated statistically significant improvements in both systolic blood pressure and sleep quality.

These findings align with recent systematic reviews and meta-analyses demonstrating the efficacy of yogic practices. Ahuja et al. ² showed that Yoga Nidra significantly reduces both systolic and diastolic blood pressure compared to control groups, while Steinmane and Fernate ³ demonstrated that breathing exercises improve sleep quality across various adult populations. Additionally, Prashanth et al. ⁴ found statistically significant sleep quality improvements in elderly populations practising yoga. Building upon these clinical findings, this letter explores the neurophysiological mechanisms underlying the sleep-promoting effects of OM chanting, pranayama and Yoga Nidra practices.

During audible OM chanting, neuroimaging studies reveal distinct patterns of brain deactivation that may explain its therapeutic effects. Kalyani et al. ⁵ reported bilateral deactivation in key limbic and paralimbic structures, including the orbitofrontal cortex, anterior cingulate cortex, parahippocampal gyri, thalami and hippocampi, with particularly notable deactivation of the right amygdala compared to rest conditions. Importantly, these changes did not occur during the control ‘ssss’ condition, suggesting specificity to OM chanting.

The authors proposed that this limbic–paralimbic deactivation may arise from vagus nerve engagement via its auricular branches, potentially triggered by the vibrational sensations experienced during audible OM chanting. ⁵ This deactivation of limbic structures, which are responsible for emotional regulation and stress responses, promotes autonomic balance and may directly contribute to improved sleep quality. ⁶

Supporting the vagal stimulation hypothesis, Inbaraj et al. ⁷ demonstrated that just five minutes of loud OM chanting produces immediate effects on autonomic function. Their study showed increased high-frequency power in heart rate variability parameters, indicating parasympathetic dominance. This autonomic shift occurs through dual mechanisms: Stimulation of laryngeal and auricular branches of the vagus nerve due to vibrational sensations and increased respiratory sinus arrhythmia achieved by decreasing respiratory frequency to approximately six breaths per minute.

The insula, a critical region for processing proprioceptive and interoceptive inputs, including pain, temperature and visceral sensations, plays a crucial role in translating bodily experiences into emotional and cognitive awareness.^{8, 9} Functional connectivity studies of OM chanting reveal significantly reduced outputs from the insula, anterior cingulate and orbitofrontal cortices during OM chanting compared to both rest and control conditions. ¹⁰ This reduction in insular output may contribute to decreased emotional reactivity and enhanced autonomic regulation.

Electroencephalogram (EEG) studies provide additional evidence for the neurophysiological effects of OM chanting. Harne and Hiwale ¹¹ demonstrated that 30 minutes of OM mantra meditation significantly alters theta wave patterns compared to baseline across all brain regions, indicating widespread reductions in cortical arousal—a state conducive to sleep initiation.

At the network level, OM chanting appears to facilitate flexible switching between resting-state networks, including the attentional network, frontoparietal control network and default mode network (DMN). ¹¹ The DMN, responsible for internal cognition, mental exploration and emotional processing, shows particular relevance to sleep regulation. Long-term OM chanting practice may shift the balance from DMN dominance toward attentional network activation. ¹² Importantly, DMN deactivation has been associated with improved sleep health, ¹³ providing a potential mechanism for the sleep-promoting effects observed in clinical studies.

Neurophysiological studies of Yoga Nidra reveal specific brainwave changes that promote sleep. Datta et al. ¹⁴ found that Yoga Nidra practice increases delta waves in select brain regions responsible for local sleep while preserving frontal region activity, indicating a unique ‘non-sleep awakened relaxed state’. This selective enhancement of delta activity is particularly significant because morning Yoga Nidra practice increases nighttime delta activity, which attenuates sympathetic activity and enhances parasympathetic regulation during sleep.^{14, 15}

Clinical studies support these neurophysiological findings. Datta et al. ¹⁵ demonstrated that Yoga Nidra practice significantly improves sleep in patients with chronic insomnia through a randomised controlled trial. The practice was associated with improved sleep architecture, enhanced cognitive processing and better performance on learning and memory tasks. ¹⁴

Slow-breathing pranayama techniques, including Nadi Shodhana (alternate nostril breathing), Ujjayi (ocean breath) and Bhramari (humming bee breath), improve sleep quality through enhanced vagal tone and attenuated sympathetic arousal. ¹⁶ Power spectral analysis during and after Bhramari pranayama reveals increased theta, alpha and gamma power in the right temporal region. ¹⁷ The increased theta activity is particularly relevant, as it is associated with relaxed, blissful or meditative states of consciousness. ¹⁷

Clinical studies demonstrate that comprehensive yoga practices incorporating asanas, pranayama, relaxation and meditation techniques are associated with reductions in anxiety and depressive symptoms, along with improvements in mood, cognitive processing and lower Pittsburgh Sleep Quality Index scores in older adults. ¹⁸

Both Yoga Nidra and pranayama practices attenuate hypothalamic–pituitary–adrenal (HPA) axis activity, supporting healthy melatonin rhythmicity, reducing cortisol levels and promoting neuroendocrine homeostasis.^{19, 20} These mechanisms collectively facilitate sleep initiation and enhance overall sleep quality through multiple convergent pathways: Autonomic rebalancing toward parasympathetic dominance, limbic system deactivation reducing emotional reactivity and stress responses, HPA axis regulation normalising stress hormone patterns, brainwave optimisation enhancing theta and delta wave activity and network level changes promoting beneficial DMN modulation.

The mechanistic insights outlined above provide a robust neurophysiological foundation for the clinical benefits observed in the study by Akshita et al. Understanding these mechanisms can inform optimal protocol design, patient selection and outcome measurement in future interventions.

However, we strongly encourage explicit monitoring and reporting of adverse events in geriatric populations, including dizziness, breathlessness, orthostatic symptoms and musculoskeletal discomfort during supine postures. Such safety data is essential for proper risk–benefit appraisal and successful implementation in clinical settings.

The neurophysiological evidence presented here elucidates the mechanisms by which OM chanting, pranayama and Yoga Nidra improve sleep quality through complementary pathways involving autonomic rebalancing, limbic deactivation, HPA axis regulation and beneficial brainwave changes. Integrating these mechanistic insights with comprehensive safety monitoring would strengthen the translational impact of home-based yogic interventions for elderly populations with hypertension and sleep disorders.