Abstract
Evidence has amassed from both animal intracranial recordings and human electrophysiology that neural oscillatory mechanisms play a critical role in a number of cognitive functions such as learning, memory, feature binding and sensory gating. The wide availability of high-density electrical and magnetic recordings (64–256 channels) over the past two decades has allowed for renewed efforts in the characterization and localization of these rhythms. A variety of cognitive effects that are associated with specific brain oscillations have been reported, which range in spectral, temporal, and spatial characteristics depending on the context. Our laboratory has focused on investigating the role of alpha-band oscillatory activity (8–14 Hz) as a potential attentional suppression mechanism, and this particular oscillatory attention mechanism will be the focus of the current review. We discuss findings in the context of intersensory selective attention as well as intrasensory spatial and feature-based attention in the visual, auditory, and tactile domains. The weight of evidence suggests that alpha-band oscillations can be actively invoked within cortical regions across multiple sensory systems, particularly when these regions are involved in processing irrelevant or distracting information. That is, a central role for alpha seems to be as an attentional suppression mechanism when objects or features need to be specifically ignored or selected against.
Highlights
Evidence has amassed from both animal intracranial recordings and human electrophysiology that neural oscillatory mechanisms play a critical role in a number of cognitive functions such as learning, memory, feature binding and sensory gating
Our laboratory has focused on investigating the role of alpha-band oscillatory activity (8–14 Hz) as a potential attentional suppression mechanism, and this particular oscillatory attention mechanism will be the focus of the current review
Since alpha oscillations (8–14 Hz) are known to be related to general alerting and ongoing visual processing (Adrian and Matthews, 1934; Klimesch et al, 1998) and are seen in the EEG, even when subjects are involved in highly demanding tasks, we proposed that such oscillations may be involved in selective attention mechanisms (Foxe et al, 1998)
Summary
Alpha and attention form of inhibited or decreased receptivity state. Evidence from behavioral studies supports such a mechanism, as reaction times to stimuli presented at non-attended locations are slower relative to those at attended locations (e.g., Posner et al, 1980), and precuing visual targets when they are presented with accompanying distracters improves performance to levels seen when no distracters were presented (Morgan et al, 1998). Some evidence suggests that one correlate of the first variety of attention, enhancement of neural processing for stimuli at the focus of attention, is the selective modulation of evoked gamma-band oscillatory activity (e.g., Gruber et al, 1999; Shibata et al, 1999; Sokolov et al, 1999; Fries et al, 2001). Vanni et al (1997) demonstrated a parieto-occipital alpha effect such that alpha level became higher in the period following presentation of a “non-object” stimulus as opposed to meaningful objects. They suggested that this represented a disengagement of attention by parietal attention gating structures in the inferior parietal region. Our results regarding this prediction from a series of studies are discussed below
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