• slow eeg activity
• altered consciousness
• phenomenology of consciousness
• nasal trigeminal stimulation
• olfactory epithelium stimulation
• eeg

It has long been known that mechanoreceptors within the olfactory epithelium have a role
in modulating brain activity during nasal respiration. This phenomenon has been
convincingly elucidated by a series of studies on the effect of nasal breathing and in
particular of those tackling with slow-paced breathing techniques proper of contemplative
practices such as Pranayama.
The aim of this thesis is to verify the after-effects of the olfactory epithelium stimulation
on brain activity and its behavioural correlates, and to disentangle the effects of this
stimulation from those (if any), related to the stimulation of nasal areas innervated by the
trigeminal nerve during periodical and slow-paced odourless-air-delivery.
The volunteers for the study are ten healthy humans without any experience in
contemplative practices. The eligibility of each volunteer was evaluated by a semistructured interview conducted by a senior physician and psychiatrist and by delivering
the Symptoms Checklist-90 questionnaire to evaluate psychopathological symptoms and
the Pittsburgh Sleep Quality Index to assess sleep quality and disturbances.
The study consists of two different experimental sessions. During each session, the
participant lays down in a darkened room and he is asked to close his eyes and to breath
normally through the mouth. During the olfactory stimulation session, the participant
wears nasal plugs with pass-through holes allowing the correct positioning of the nasal
cannulas used for air delivery. Each session starts with a 7-minutes resting-state phase
followed by 15 minutes of nasal stimulation and ends with another 7-minutes restingstate phase. Two different stimulation modalities are applied (one for each session):
1. Stimulation of the olfactory epithelium: 15 minutes of odourless air delivery at
0.05Hz (8 s of delivery, 12s off), in line with slow-paced breathing rhythms
typical of contemplative practices (i.e. Pranayama breathing).
2. Stimulation of peripheral nasal areas innervated by the trigeminal nerve. The
airflow is delivered to nasal areas innervated only by the trigeminal nerve. In this
session nasal plugs without pass-through holes are used to prevent the flow of air
towards the olfactory epithelium.
Throughout each session, ECG and respiratory signals together with high-density EEG
have been recorded. At the end of the session, two psychometric questionnaires are
delivered: the Phenomenology of Consciousness Inventory, elucidating the
phenomenological aspects of consciousness associated to the experience and the State
Anxiety Inventory to assess putative changes of anxiety levels.
Based on results from previous studies, the expected after-effects of olfactory epithelium
stimulation were a slowing of brain rhythms (increase of delta and theta bands activity),
over the whole cortical mantle session associated with a modification in the subjective
perception of the self and to the sensation of having experienced an altered state of
consciousness. It is worth underlining how the former control condition is specifically
designed to unambiguously demonstrate the modulatory role of the olfactory epithelium,
while the latter condition aims at identifying the modulatory effects of trigeminal nerve
stimulation (if any). This allows to ascertain whether the effects of the olfactory
epithelium stimulation are partially ascribable to the stimulation of trigeminal nerves, as
the intranasal trigeminal system is closely connected to the olfactory epithelium itself.