Evidence of Two Distinct Alpha Rhythms Underlying Attention

In human brains, populations of excitatory neurons often synchronize through interactions with inhibitory neurons to facilitate information transfer. Such synchronized neural activities produce macroscopic oscillatory changes in electrical potential, which can be detected with electroencephalography (EEG). Analysis of the various frequency components of the EEG signal reveals that synchronization occurs in several frequency bands (alpha, beta, gamma, etc. ), each associated with different cognitive roles. The amount of synchronization within each of these bands, measured by power, changes with cognitive tasks. In visual attention, oscillations in the alpha frequency range (8–12 Hz) are typically observed over posterior brain areas in humans when these areas are not engaged in a task. Moreover, shifts of attention to one visual hemifield are associated with increased posterior alpha power in the ipsilateral hemisphere, which receives information from the unattended hemifield, while posterior alpha power decreased in the contralateral hemisphere, which processes information from the attended hemifield (Worden et al. , 2000). The increased alpha power in the ipsilateral hemisphere is thought to reflect inhibition of processing of distracting information from the unattended hemifield, while decreased alpha power in the contralateral hemisphere is thought to remove such functional Inhibition, enhancing information processing from the attended hemifield (Worden et al. , 2000; Klimesch et al. , 2007; Jensen and Mazaheri, 2010). This unidimensional and relatively simple understanding of lateral alpha modulation (Worden et al. , 2000) was challenged recently by evidence showing that spatial attention involves not one, but several rhythms within the alpha band. For example, source analysis revealed that spatially segregated brain regions generated alpha rhythms with distinct temporal dynamics during attentional processing (Capilla et al. , 2014; Sokoliuk et al. , 2019). Similarly, spatiotemporal analysis found that two alpha rhythms propagate in different directions, reflecting different functional roles in spatial attention (Alamia et al. , 2023). Given … Correspondence should be addressed to Yifan Zeng at yifan. zengatpsychologie. uzh. ch.