Abstract
Alpha-frequency band (8–14 Hz) oscillations are among the most salient phenomena in human electroencephalography (EEG) recordings and yet their functional roles have remained unclear. Much of research on alpha oscillations in human EEG has focused on peri-stimulus amplitude dynamics, which phenomenologically support an idea of alpha oscillations being negatively correlated with local cortical excitability and having a role in the suppression of task-irrelevant neuronal processing. This kind of an inhibitory role for alpha oscillations is also supported by several functional magnetic resonance imaging and trans-cranial magnetic stimulation studies. Nevertheless, investigations of local and inter-areal alpha phase dynamics suggest that the alpha-frequency band rhythmicity may play a role also in active task-relevant neuronal processing. These data imply that inter-areal alpha phase synchronization could support attentional, executive, and contextual functions. In this review, we outline evidence supporting different views on the roles of alpha oscillations in cortical networks and unresolved issues that should be addressed to resolve or reconcile these apparently contrasting hypotheses.
Highlights
Human perceptual and mental experiences are serial, introspectively coherent, and have a limited capacity of three to four objects (Luck and Vogel, 1997; Marois et al, 2004; Vogel and Machizawa, 2004)
We explore some recent studies addressing the functional correlates of alpha-band phase and amplitude dynamics both in local and large-scale cortical networks from the viewpoints of two alternative, albeit not mutually incompatible, hypotheses: the inhibition hypothesis and the active-processing hypothesis
We suggest that the inhibition and active-processing hypotheses could be reconciled by considering that inhibition at lower sensory and motor levels is, a key property of the higher-level frontal functions (Aron et al, 2004; Congdon et al, 2010), and could be mechanistically achieved by top-down alpha phase interactions
Summary
Human perceptual and mental experiences are serial, introspectively coherent, and have a limited capacity of three to four objects (Luck and Vogel, 1997; Marois et al, 2004; Vogel and Machizawa, 2004). There appears to be a mechanistic transition so that active-processing in early sensory regions is associated with decreased alpha amplitudes and attenuated synchronization (Bollimunta et al, 2008, 2011) whereas in attentional, executive, and higher-level sensory regions, alpha amplitude (Mo et al, 2011), and synchronization (von Stein et al, 2000) are positively correlated with task-related neuronal processing and local cortical excitability.
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