Neural Origin of Spontaneous Hemodynamic Fluctuations in Rats under Burst–Suppression Anesthesia Condition

摘要

Spontaneous hemodynamic signals fluctuate coherently within many resting-brain functional networks not only in awake humans and lightly anesthetized primates but also in animals under deep anesthesia characterized by burst–suppression electroencephalogram (EEG) activity and unconsciousness. To understand the neural origin of spontaneous hemodynamic fluctuations under such a deep anesthesia state, epidural EEG and cerebral blood flow (CBF) were simultaneously recorded from the bilateral somatosensory cortical regions of rats with isoflurane-induced burst–suppression EEG activity. Strong neurovascular coupling was observed between spontaneous EEG “bursts” and CBF “bumps,” both of which were also highly synchronized across the 2 hemispheres. Functional magnetic resonance imaging (fMRI) was used to image spontaneous blood oxygen level–dependent (BOLD) signals under the same anesthesia conditions and showed similar BOLD “bumps” and dependence on anesthesia depth as the CBF signals. The spatiotemporal BOLD correlations indicate a strong but less-specific coherent network covering a wide range of cortical regions. The overall findings reveal that the spontaneous CBF/BOLD fluctuations under unconscious burst–suppression anesthesia conditions originate mainly from underlying neural activity. They provide insights into the neurophysiological basis for the use of BOLD- and CBF-based fMRI signals for noninvasively imaging spontaneous and synchronous brain activity under various brain states.