Cause or consequence? Alpha oscillations in visuospatial attention

Modulations of electroencephalogram alpha amplitude have long been associated with visuospatial attention, but whether alpha power changes are causally involved in attention shifts or reflect a consequence of them is a matter of ongoing debate. We evaluate recent findings providing evidence for both of these two perspectives. We discuss the extent to which the temporal dynamics of alpha activity and extrinsic modulation of alpha amplitude can be used as a basis for arguing for or against alpha activity as a causal substrate of visuospatial attention. We also discuss whether alpha activity implements attention by gain control in the early visual cortex. A potential mechanism by which alpha activity in higher visual areas implements attentional gating is introduced. A well-established finding in the literature of human studies is that alpha activity (rhythmical brain activity around 10 Hz) shows retinotopic amplitude modulation during shifts in visual attention. Thus, it has long been argued that alpha amplitude modulation might play a crucial role in attention-driven alterations in visual information processing. Recently, there has been a revival of the topic, driven in part by new studies directly investigating the possible causal relationship between alpha activity and responses to visual input, both neuronally and perceptually. Here, we discuss evidence for and against a causal role of alpha activity in visual attentional processing. We conclude with hypotheses regarding the mechanisms by which top-down-modulated alpha activity in the parietal cortex might select visual information for attentive processing. A well-established finding in the literature of human studies is that alpha activity (rhythmical brain activity around 10 Hz) shows retinotopic amplitude modulation during shifts in visual attention. Thus, it has long been argued that alpha amplitude modulation might play a crucial role in attention-driven alterations in visual information processing. Recently, there has been a revival of the topic, driven in part by new studies directly investigating the possible causal relationship between alpha activity and responses to visual input, both neuronally and perceptually. Here, we discuss evidence for and against a causal role of alpha activity in visual attentional processing. We conclude with hypotheses regarding the mechanisms by which top-down-modulated alpha activity in the parietal cortex might select visual information for attentive processing. neural oscillatory activity in a frequency range around 10 Hz in humans. It has been claimed that the amplitude of alpha activity is associated with cortical excitability. the excitatory part of a neural oscillation’s cycle. Usually the duty cycle is characterized by increased neuronal firing. alignment of intrinsic oscillatory brain activity using stimulation approaches, usually rhythmic ones, such as sensory, electrical, magnetic, or ultrasonic stimulation. This might lead to increased amplitude at respective and/or related frequency ranges or it could result in alignment of the neural oscillation’s instantaneous phase. adjustment of neural activity to put greater or lesser weight on the processing of a specific incoming stimulus. Gain control has been discussed, for instance, to reflect a physiological correlate of a spotlight of attention in the early visual cortex [61.Brefczynski J.A. DeYoe E.A. A physiological correlate of the “spotlight” of visual attention.Nat. Neurosci. 1999; 2: 370-374Crossref PubMed Scopus (607) Google Scholar]. a neural mechanism to modulate the flow of low-level information to higher visual cortical areas. noninvasive techniques to modulate brain activity. Examples of NIBS techniques are TMS and tES. TMS alters neuronal activity by means of electromagnetic pulses generated by a coil that is held against the participant’s scalp. tES stimulates neuronal tissue by means of electric currents applied via electrodes attached to the scalp. To gear into ongoing oscillatory brain activity, a series of electromagnetic pulses (rTMS) or rhythmical fluctuations of electrical current (tACS) can be delivered. a measure of the presence and strength of a systematic relationship between the phase of two distinct neural oscillations (e.g., at different brain sites, with different frequencies). Phase coherence is high if the phase relationship is consistent over time (usually across trials) and low if the phase relationship varies randomly. experimental paradigm to investigate the shifting of visuospatial attention. Participants are asked to keep their gaze at a fixation cross in the middle of a screen. Then, the left or the right visual hemifield is cued. Participants are asked to covertly shift their visual attention into the cued hemifield (i.e., without moving their eyes). This is followed by the presentation of a visual target stimulus either in the attended visual hemifield (valid trial) or in a smaller proportion of trials in the unattended hemifield (invalid trial). an ERP (i.e., a neural response observable after averaging neural activity over a large number of trials) elicited by a series of rhythmically displayed visual stimuli, which is characterized by an increase in amplitude and a rhythmic amplitude modulation persisting throughout the stimulation. It is modulated by attentional processing, as indicated by an increase in amplitude in response to attended stimuli relative to unattended stimuli.