Selective blockade of rat brain T-type calcium channels provides insights on neurophysiological basis of arousal dependent resting state functional magnetic resonance imaging signals

Abstract

A number of studies point to slow (0.1–2 Hz) brain rhythms as the basis for the resting-state functional magnetic resonance imaging (rsfMRI) signal. Slow waves exist in the absence of stimulation, propagate across the cortex, and are strongly modulated by vigilance similar to large portions of the rsfMRI signal. However, it is not clear if slow rhythms serve as the basis of all neural activity reflected in rsfMRI signals, or just the vigilance-dependent components. The rsfMRI data exhibit quasi-periodic patterns (QPPs) that appear to increase in strength with decreasing vigilance and propagate across the brain similar to slow rhythms. These QPPs can complicate the estimation of functional connectivity (FC) via rsfMRI, either by existing as unmodeled signal or by inducing additional wide-spread correlation between voxel-time courses of functionally connected brain regions. In this study, we examined the relationship between cortical slow rhythms and the rsfMRI signal, using a well-established pharmacological model of slow wave suppression. Suppression of cortical slow rhythms led to significant reduction in the amplitude of QPPs but increased rsfMRI measures of intrinsic FC in rats. The results suggest that cortical slow rhythms serve as the basis of only the vigilance-dependent components (e.g., QPPs) of rsfMRI signals. Further attenuation of these non-specific signals enhances delineation of brain functional networks.

Variation in the Distribution of Large-scale Spatiotemporal Patterns of Activity Across Brain States

“…Despite the prominence of QPPs in rs-fMRI, little is known about the mechanisms that organize brain-wide activity into these few repeated spatiotemporal patterns. Multimodal studies have linked them to infraslow neural activity 40,41 , which is itself understudied, and QPPs exhibit reduced magnitude when slow waves are suppressed 42 . Structural connectivity undoubtedly plays a role in the organization of intrinsic brain activity, as shown by modeling studies that recreate much of the structure of functional connectivity by using a network representation of the brain's structural connections along with a variety of neural mass models.…”