Abstract
The brain constitutes a formidably complicated structural network. There are three main types of connectivity used to describe neuronal networks, which reflect three parallel levels of investigation: anatomical connectivity, functional connectivity and effective connectivity. Effective connectivity indicates the direct influence that a node exerts on another, and in the context of neuronal circuits, a causal relationship between the activities of two nodes. Since its definition, effective connectivity analysis has been used to describe causal relationship across multiple spatial scales in PET imaging, fMRI, electroencephalography (EEG) and magnetoencephalography (MEG), single-unit, and local field potential. There are diverse literatures which probe the anesthetized state using effective connectivity analysis over the past two decades. The examination of effective connectivity in the anesthetized state is of relevance to both anesthesiologists and neuroscientists, as it has the potential to elucidate still unclear mechanisms of anesthesia while offering insight into intrinsic functional activity in the brain. The present review attempts to examine, elucidate, and integrate the insight that effective connectivity analysis of the anesthetized state has generated thus far.
Highlights
Since the nineteenth century, we have known that the neuronal elements of the brain constitute a formidablyHow to cite this paper: Xu, X.Y., Wang, G.L. and Tian, X. (2015) Effects of Anesthesia on Effective Connectivity in the Brain
Other measures related to spectral Granger Causality (GC) have been proposed, such as the Directed Transfer Function (DTF) [17], the Partial Directed Coherence (PDC), which might be numerically and computationally advantageous when compared to any of the above measures [18]
In order to overcome methodological limitations of EEG methods, Jordan et al recorded simultaneously resting-state EEG and blood oxygen level-dependent fMRI of healthy subjects during consciousness and propofol-induced loss of consciousness (LOC) [45]. They found that changes in functional connectivity in fMRI during unconsciousness correlate with simultaneous changes in effective connectivity in EEG
Summary
We have known that the neuronal elements of the brain constitute a formidably. Such networks are thought to provide the physiological basis for information processing and mental representations [3]-[6]. Functional connectivity indicates a statistical dependence between the activities of two nodes without any assumption of the mechanism by which these relationships are mediated. Effective connectivity indicates the direct influence that a node exerts on another, and in the context of neuronal circuits, a causal relationship between the activities of two nodes [7]. The effective connectivity takes explicitly into consideration the existence of a causal link between two or more brain regions [8]
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