Ultra-fast magnetic resonance encephalography of physiological brain activity – Glymphatic pulsation mechanisms?

Abstract

The theory on the glymphatic convection mechanism of cerebrospinal fluid holds that cardiac pulsations in part pump cerebrospinal fluid from the peri-arterial spaces through the extracellular tissue into the peri-venous spaces facilitated by aquaporin water channels. Since cardiac pulses cannot be the sole mechanism of glymphatic propulsion, we searched for additional cerebrospinal fluid pulsations in the human brain with ultra-fast magnetic resonance encephalography. We detected three types of physiological mechanisms affecting cerebral cerebrospinal fluid pulsations: cardiac, respiratory, and very low frequency pulsations. The cardiac pulsations induce a negative magnetic resonance encephalography signal change in peri-arterial regions that extends centrifugally and covers the brain in &1 Hz cycles. The respiratory &0.3 Hz pulsations are centripetal periodical pulses that occur dominantly in peri-venous areas. The third type of pulsation was very low frequency (VLF 0.001-0.023 Hz) and low frequency (LF 0.023-0.73 Hz) waves that both propagate with unique spatiotemporal patterns. Our findings using critically sampled magnetic resonance encephalography open a new view into cerebral fluid dynamics. Since glymphatic system failure may precede protein accumulations in diseases such as Alzheimer's dementia, this methodological advance offers a novel approach to image brain fluid dynamics that potentially can enable early detection and intervention in neurodegenerative diseases.

Altered physiological brain variation in drug‐resistant epilepsy

“…In human brain, glymphatic system may be driven partially by respiratory and vasomotor control waves in addition to cardiac pulses (Kiviniemi et al., 2016). …”

“…The results of our study suggest that the physiological pulsations, that drive glymphatic clearance, may be abnormal in drug‐resistant epileptic brain (Kiviniemi et al., 2016; Nedergaard, 2013). As none of our DRE patients had MTS lesions, we suggest that seemingly normal DRE patients’ brain tissue may suffer from failed physiological drive of the glymphatic clearance, rather than direct AQP4 channel loss as in MTS.…”

“…FIX method was trained on previously acquired control data and was used for both groups because of our null hypothesis. The first 5‐min data, that is, 3,000 brain volumes were used for the actual CV MREG calculations as in our previous study and to minimize vigilance drops (Kiviniemi et al., 2016). Data from patient 4 were excluded for the first measurement group analysis due to partial data corruption.…”

“…This methodology enables robust mapping of epileptic spike activity as detected in simultaneous EEG‐fMRI due to the increased temporal accuracy and statistical power (Jacobs et al., 2014). MREG can also discern three different forms of physiological brain pulsations; cardiac pulses, respiratory oscillations, and very low‐frequency fMRI signal fluctuations (Kiviniemi et al., 2016). These are important for the detection of driving forces of recently detected glymphatic brain clearance mechanisms, which have been linked to several neurological diseases (Sun et al., 2017).…”

Surgical Treatment for Neonatal Hydrocephalus: Catheter-Based Cerebrospinal Fluid Diversion or Endoscopic Intervention?

“…Thus, the therapeutic principle is to restore CSF outflow dynamics and to reestablish physiological pulsatile forces [16]. This can either be achieved by neurosurgical removal of the occluding structure (e.g.…”