Alpha Oscillations Correlate with the Successful Inhibition of Unattended Stimuli

Abstract

Because the human visual system is continually being bombarded with inputs, it is necessary to have effective mechanisms for filtering out irrelevant information. This is partly achieved by the allocation of attention, allowing the visual system to process relevant input while blocking out irrelevant input. What is the physiological substrate of attentional allocation? It has been proposed that alpha activity reflects functional inhibition. Here we asked if inhibition by alpha oscillations has behavioral consequences for suppressing the perception of unattended input. To this end, we investigated the influence of alpha activity on motion processing in two attentional conditions using magneto-encephalography. The visual stimuli used consisted of two random-dot kinematograms presented simultaneously to the left and right visual hemifields. Subjects were cued to covertly attend the left or right kinematogram. After 1.5 sec, a second cue tested whether subjects could report the direction of coherent motion in the attended (80%) or unattended hemifield (20%). Occipital alpha power was higher contralateral to the unattended side than to the attended side, thus suggesting inhibition of the unattended hemifield. Our key finding is that this alpha lateralization in the 20% invalidly cued trials did correlate with the perception of motion direction: Subjects with pronounced alpha lateralization were worse at detecting motion direction in the unattended hemifield. In contrast, lateralization did not correlate with visual discrimination in the attended visual hemifield. Our findings emphasize the suppressive nature of alpha oscillations and suggest that processing of inputs outside the field of attention is weakened by means of increased alpha activity.

α-Oscillations in the monkey sensorimotor network influence discrimination performance by rhythmical inhibition of neuronal spiking

“…We found that decreases in α-activity during the decision period correlated with task performance in S1, S2, DPC, MPC-left, and M1. The current findings are consistent with previous work showing that somatosensory α-activity influences discrimination performance (18,27) and with the visuospatial attention literature linking α-activity to detection performance (15)(16)(17). These previous findings have resulted in the notion that α-activity is involved in sensory gating.…”

“…In particular, α-activity might serve to shape the state of sensory brain regions to direct the flow of information and optimize performance (8). In support of this idea, several studies on visual perception have shown that anticipatory α-activity reflects the orienting of attention (9)(10)(11)(12)(13)(14) and influences detection performance (15)(16)(17). Recently, it was shown that the functionality of α-oscillations can be generalized to the somatosensory system (18)(19)(20)(21).…”

Top-Down Controlled Alpha Band Activity in Somatosensory Areas Determines Behavioral Performance in a Discrimination Task

“…Further, it is in line with results from the visual domain: higher ongoing visual alpha activity has been related to lower visual detection performance van Dijk et al, 2008). Furthermore, alpha lateralization over parieto-occipital regions has been correlated with detection of attended and successful inhibition of unattended visual stimuli (Thut et al, 2006;Händel et al, 2011). Recent TMS studies entraining posterior alpha oscillations strongly suggest that the influence of alpha activity on perception is causal rather than merely correlational (Sauseng et al, 2009;Romei et al, 2010).…”

“…In visual spatial attention tasks, alpha activity shows a lateralized pattern: alpha decreases contralateral to the attended location (Sauseng et al, 2005) and increases contralateral to the ignored location, presumably to suppress distracting input (Worden et al, 2000;Kelly et al, 2006). This lateralized alpha activity correlates with visual detection performance (Thut et al, 2006;Händel et al, 2011). The functionality of alpha might be generalized to other modalities.…”

Alpha-band suppression in the visual word form area as a functional bottleneck to consciousness

“…This could be convincingly pointed out by its left-lateralized activity pattern irrespective of response-hand laterality ( Figure 7A), and by the non-motor region in which it was generated, namely, the LOT Noteworthy, a recently proposed framework postulates that alpha activity reflects functional inhibition (Jensen and Mazaheri, 2010). This interpretation was derived from reports of alpha power suppression in task-engaged brain areas (van Gerven and Jensen, 2009;Handel et al, 2010), and alternatively of alpha power enhancement in non-engaged areas (Haegens et al, 2010). Thus, alpha suppression as observed here could be indicative of the functional engagement of the LOT as a selective activation pattern gating fully conscious perception of words.…”