Brain connectivity in rat at rest: Analysis of dynamic signals using fMRI and electrophysiology studies

Abstract

Collections of afferent and efferent connections and associated neuroelectric activities provide a framework for constructing brain connectivity networks. Advances in neural signal acquisition and analysis methods improved the understanding of both structural and functional aspects of the neurofunctional networks. In particular, based on the strong coupling between neural and hemodynamic activities, blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) has long been established as a convenient means to evaluate stimulus-induced activity in the brain with excellent spatial resolution. However, the fMRI technique is limited to resolve only stimuli- or task-specific responses and to assess the functionality of responding brain regions. An alternative, a relatively new fMRI approach, resting-state fMRI (rs-fMRI) has been introduced to evaluate organization of the functional connectivity networks and changes of such in the whole brain. The rs-fMRI relies on periodic spontaneous neurohemodynamic events and related MRI signal changes due to fluctuations of the deoxygenated hemoglobin concentration in the local brain tissue. We posit that such unsolicited neural activities are particularly important and useful for understanding baseline of the functional neural networks and also for assessing neuropathological conditions such as stroke, ALS, alzheimer’s and parkinson’s dieseases. In mid 1990’s, low-frequency (~0.1 Hz) fluctuations (LFFs) have been identified in the resting-state BOLD MRI time series. Since the discovery, researchers have demonstrated the temporal synchronicity of LFFs across functionally related brain regions. Several studies have substantiated the neural basis of LFFs while correlations between fMRI time series have expanded the applicability of BOLD fMRI from a tool to assess task-elicited brain activity to one that can be used to construct global maps of neural connectivity networks. However, since the BOLD signal is an i...