Nasal airflow promotes default mode network activity.

BACKGROUND AND OBJECTIVES: Default mode network (DMN) is a principal network that is more active at the baseline functional state of consciousness and spontaneous brain activity. Nasal breathing beyond the oxygen supply, entrained brain oscillations in widespread brain regions. Consistent with the important role of nasal breathing on neural oscillation for brain function, here we aimed to evaluate respiration entrained DMN rhythms. MATERIALS AND METHODS: Using electroencephalography (EEG), we assessed the power spectral density and connectivity in DMN during the resting state among a group of sixteen healthy during three successive sessions. In addition to DMN, synchrony of the signal over the widespread cortical regions including somatosensory areas was investigated. Signal acquisition sessions consist of three times including nasal breathing, oral breathing, and nasal air-puff state that odorless air was puffed using a nasal cannula via an electrical valve (open duration of 630 ms) with a frequency of 0.2 Hz while subjects spontaneously breath orally. RESULTS: Our analyses demonstrated that nasal airflow, during both nasal breathing and nasal air-puff states, enhanced the power and connectivity of DMN regions specially at higher frequency bands, particularly gamma ranges. Enhancement in brain areas activity and connectivity including DMN and somatosensory due to the nasal airflow were not affected even in the condition that subjects were not attending to the nasal air-puff. CONCLUSIONS: Nasal airflow promotes brain oscillations, particularly at the range of gamma that is very essential for higher brain functions.

Nasal Air Puff Promotes Default Mode Network Activity in Mechanically Ventilated Comatose Patients: A Noninvasive Brain Stimulation Approach.

OBJECTIVES: Coma state and loss of consciousness are associated with impaired brain activity, particularly gamma oscillations, that integrate functional connectivity in neural networks, including the default mode network (DMN). Mechanical ventilation (MV) in comatose patients can aggravate brain activity, which has decreased in coma, presumably because of diminished nasal airflow. Nasal airflow, known to drive functional neural oscillations, synchronizing distant brain networks activity, is eliminated by tracheal intubation and MV. Hence, we proposed that rhythmic nasal air puffing in mechanically ventilated comatose patients may promote brain activity and improve network connectivity. MATERIALS AND METHODS: We recorded electroencephalography (EEG) from 15 comatose patients (seven women) admitted to the intensive care unit because of opium poisoning and assessed the activity, complexity, and connectivity of the DMN before and during the nasal air-puff stimulation. Nasal cavity air puffing was done through a nasal cannula controlled by an electrical valve (open duration of 630 ms) with a frequency of 0.2 Hz (ie, 12 puff/min). RESULTS: Our analyses demonstrated that nasal air puffing enhanced the power of gamma oscillations (30-100 Hz) in the DMN. In addition, we found that the coherence and synchrony between DMN regions were increased during nasal air puffing. Recurrence quantification and fractal dimension analyses revealed that EEG global complexity and irregularity, typically seen in wakefulness and conscious state, increased during rhythmic nasal air puffing. CONCLUSIONS: Rhythmic nasal air puffing, as a noninvasive brain stimulation method, opens a new window to modifying the brain connectivity integration in comatose patients. This approach may potentially influence comatose patients' outcomes by increasing brain reactivity and network connectivity.

Distraction of olfactory bulb-medial prefrontal cortex circuit may induce anxiety-like behavior in allergic rhinitis.

Allergic rhinitis is a chronic inflammatory disease of the upper respiratory tract, which is associated with high incidence of anxiety symptom. There is evidence that medial prefrontal cortex modulates anxiety-related behaviors and receives projections from olfactory bulb. Since olfactory dysfunction has been reported in allergic rhinitis, we aimed to evaluate anxiety-like behavior and oscillations of olfactory bulb-medial prefrontal cortex circuit in an animal model of allergic rhinitis. The number of open arm entries in elevated zero maze was significantly reduced in sensitized rats exposed to intranasal ovalbumin compared to the control group, which was indicating the enhancement of anxiety-like behavior in allergic rhinitis animals. Analysis of local field potentials in olfactory bulb and medial prefrontal cortex during immobility and exploration state showed that anxiety-like behavior induced by allergic rhinitis was in association with increased activity of medial prefrontal cortex and enhancement of olfactory bulb-medial prefrontal cortex coupling in delta and theta bands. Moreover, in allergic rhinitis animals, theta strongly coordinates local gamma activity in olfactory bulb and medial prefrontal cortex, which means to have a strong local theta/gamma coupling. We suggested that disruption of olfactory bulb-medial prefrontal cortex circuit due to allergic reactions might have a governing role for inducing anxiety-like behavior in the allergic rhinitis experimental model.