Table 1.

An overview of the numerous bio-signal markers that demonstrate stress reduction by yoga

Literature cited	Target	Yoga form	Bio-signal	Feature select	Implication
[18]	Stress	Pranakarshan pranayama and Yoga nidra	EEG and GSR	RP and change in impedance of skin	Reduction in stress
[19]	Stress	Sudharshana Kriya	EEG	Energy	Reduction in stress
[20]	Mental stress	Sudarshan Kriya	EEG and ECG	PSD and HRV	Decrement in mental stress
[21]	Stress and anxiety	Alternate nostril yoga breathing	EEG	RP	Reduction in stress and anxiety
[22]		Bhramari pranayama	EEG	PSD	Alpha band functional network structure integrates better during and after yoga
[41]	ANS	Integrated yoga-based intervention	ECG	HRV	Increased PNS activity
[42]	Anxiety	Tai chi	EKG and EEG	PSD	Decreased anxiety and increased EEG theta activity
[43]	Stress	Vipassana	EEG	PSD	Increased occipital gamma power
[44]		Zen meditation	EEG and ECG	AP and low frequency/high-frequency ratio	Internalized attention
[45]		Zen meditation	EEG	Spectral powers	Zen meditation increased the state of consciousness
[47]		Transcendental meditation	EEG	Coherence	Stabilization attentional awareness
[50]		Bhramari Pranayama	EEG	Gamma wave	Generate controlled high-frequency gamma waves
[53]		Nonreferential compassion meditation	EEG	RP
[56]	Stress	Shambhavi Maha Mudra	EEG	Spectral analysis	Higher level of mental consciousness
[63]	The spinally mediated reflex response	Medical yoga therapy	EMG	Nociceptive flexion reflex	Reduce stress
[66]	State of consciousness	“OM” chanting	EEG and GSR	RP and change in impedance of the skin	Alleviating stress
[67]	Stress	Abdominal breathing	GSR	Skin resistance	Reducing the stress level
[70]	Stress	Mindfulness meditation	fMRI	Resting-state functional connectivity	Stress reduction effects
[71]	Depression	Hatha yoga	fMRI	Functional connectivity	Reduce depressive symptomatology
[72]	Cognitive aging	Hatha yoga	fMRI	Functional connectivity	Influences healthier cognitive aging process
[74]	Depression and epilepsy	“OM” chanting	fMRI	Neuro-hemodynamic	Potential role of this “OM” chanting in clinical practice
[75]	Anxiety	Bhastrika Pranayama	fMRI	Functional connectivity	Significantly reduce the levels of anxiety
[84]	Autonomic reactivity	Mukh Bhastrika	ECG	HRV	Increase in PNS activity

PNS: Parasympathetic, ANS: Autonomic nervous system, RP: Relative power, AP: Absolute power, PSD: Power spectral density, HRV: Heart rate variability, ECG: Electrocardiogram, fMRI: Functional magnetic resonance imaging, GSR: Galvanic skin response, EEG: Electroencephalogram, EMG: Electromyogram, EKG: Electrocardiogram