The psychophysiological effects of active and passive stimulation of the olfactory epithelium: a physiological model for explaining how slow nasal breathing induces altered states of consciousness in meditation
Nasal breath is at the foundation of yoga and pranayama traditions, yet little is known about its functions on mind and brain. Based on increasing evidence from animal and human models, the aim of this thesis is to investigate psychophysiological effects of air-dependent stimulation of the olfactory epithelium in humans. In Section 1, 16 meditators performed a slow breathing task, firstly breathing through the nose and then through the mouth. EEG, cardiac and respiratory signals, and psychometric questionnaires were acquired. Significant differences were found during nasal breathing in power and connectivity in delta, theta, beta EEG brainwaves, and in the state of consciousness. In Section 2, the olfactory epithelium of 12 healthy subjects was stimulated with periodical odorless air-delivery. EEG and respiratory data, psychometric questionnaires and cognitive functions were measured. Compared with a no-stimulation session, the stimulation induced: an enhancement of delta-theta EEG activity in limbic and default mode structures; a reversal of the information flow directionality; the induction of an altered state of consciousness. In Section 3, a systematic review on slow breathing techniques was conducted, finding significant roles of the parasympathetic nervous system (increased HRV and LF power) and of cortical modulation (increased alpha and decreased theta power), in emotional and psychological well-being. Taken together, results consider two mechanisms for nasal breathing: parasympathetic dominance depending on the regulation of breathing frequency; rhythmic activity of mechanoceptors on the nasal vault modulating olfactory bulb activity, and in turn the entire cortical mantle.
