Orexin effect on physiological pulsations of the human brain

Area of Science:

• Neuroscience
• Fluid Dynamics
• Sleep Medicine

Background:

• Sleep facilitates cerebrospinal fluid (CSF) to interstitial fluid (ISF) exchange, driven by brain pulsations, particularly vasomotion and arterial pulsations.
• Noradrenergic signaling, influenced by arousal states, plays a key role in intracranial fluid dynamics and CSF-ISF clearance.

Purpose of the Study:

• To investigate brain pulsation profiles in Narcolepsy type 1 (NT1) patients as a model for orexin-targeted, sleep-related pathology.
• To assess the sensitivity of magnetic resonance encephalography (MREG) in detecting flow-related signal changes using a phantom model.
• To compare brain pulsation dynamics between healthy awake individuals, healthy sleeping individuals, and awake NT1 patients.

Main Methods:

• Fast functional MRI (fMRI) was used to map brain pulsations in three groups: healthy sleeping controls (n=13), healthy awake controls (n=79), and awake NT1 patients (n=21).
• Analysis included measuring very low frequency (0.008–0.1 Hz) and cardiorespiratory frequencies.
• Metrics like coefficient of variation, spectral power, and spectral entropy were calculated to generate brain pulsation maps.

Main Results:

• A distinct brain pulsation profile was identified, differing across healthy wakefulness, sleep, and NT1 pathology.
• NT1 patients exhibited significant alterations in vascular-related vasomotor and brain arterial pulsations compared to healthy controls.
• The study demonstrated MREG's sensitivity to flow changes and confirmed brain pulsations in both healthy wake and sleep states.

Conclusions:

• Loss of orexinergic signaling in NT1 alters brain hydrodynamics, specifically affecting vascular and arterial pulsations.
• Brain pulsation patterns provide insights into the impact of neurotransmitter deficits on brain fluid dynamics.
• MREG is a viable tool for detecting flow-related changes and characterizing brain pulsations.