Two spatially distinct posterior alpha sources fulfill different functional roles in attention

Abstract

Directing attention helps to extract relevant information and suppress distracters. Alpha brain oscillations (8-12Hz) play a fundamental role in this process, with a power decrease facilitating processing of important information and power increase inhibiting brain regions processing irrelevant information. Evidence for this phenomenon arises from visual attention studies (Worden et al., 2000), however, the effect also exists in other modalities, including the somatosensory system (Haegens et al., 2011) and inter-sensory attention tasks (Foxe and Snyder, 2011). We investigated what happens when attention is divided between two modalities using both a multi-and unimodal attention paradigm while recording EEG over 128 scalp electrodes in two separate experiments. In Experiment 1 participants divided their attention between the visual and somatosensory modality to determine the temporal or spatial frequency of a target stimulus (vibrotactile stimulus or Gabor grating). In Experiment 2, participants divided attention between two visual hemifields to identify the orientation of a target Gabor grating. In both experiments, pre-stimulus alpha power in visual areas decreased linearly with increasing attention to visual stimuli. In contrast, alpha power in parietal areas showed lower pre-stimulus alpha power when attention was divided between modalities, compared to unimodal attention.These results suggest that there are two different alpha sources, where one reflects the 'visual spotlight of attention' and the other reflects attentional effort. To our knowledge, this is the first study to show that attention recruits two spatially distinct alpha sources in occipital and parietal brain regions, which act simultaneously but serve different functions in attention.. CC-BY-NC-ND 4.0 International license It is made available under a (which was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint . http://dx.doi.org/10.1101/384065 doi: bioRxiv preprint first posted online Aug. 3, 2018; 3 SIGNIFICANCE STATEMENT Attention to one spatial location/sensory modality leads to power changes of alpha oscillations (~10Hz) with decreased power over regions processing relevant information and power increases to actively inhibit areas processing 'to-be-ignored' information. Here, we used detailed source modelling to investigate EEG data recorded during separate uni-modal (visual) and multi-(visual and somatosensory) attention tasks. Participants either focused their attention on one modality/spatial location or directed it to both. We show for the first time two distinct alpha sources are active simultaneously but play different roles. A sensory (visual) alpha source was linearly modulated by attention representing the 'visual spotlight of attention'. In contrast, a parietal alpha source was modulated by attentional effort, showing lowest alpha power when attention was divided.

Addressing challenges of high spatial resolution UHF fMRI for group analysis of higher‐order cognitive tasks: An inter‐sensory task directing attention between visual and somatosensory domains

“…The quadratic response to the direction of attention between modalities has been documented in our parallel EEG‐study using the same paradigm (Sokoliuk et al ()). In our four conditions we linearly increase visually‐directed‐attention with condition number (1–4, Figure c) whilst simultaneously linearly decreasing somatosensory‐directed‐attention with condition number (1–4, Figure d).…”

“…Analysing these two contrasts is aimed at mapping the attentional changes within these two modalities. However in the Hard (40/60,60/40) > Easy tasks (0/100,100/0) this contrast resembles a quadratic function when formulated over the 4 conditions ( Figure 3e) [as in Sokoliuk et al, 2018] with the shape reflecting variation in total attentional load.…”

Attention explores space periodically at the theta frequency

“…Alpha has been related to sensory aspects of visual perception, and was first described as the natural frequency of the occipital pole (Rosanova et al, 2009). Recent studies have further proposed multiple alpha sources (i.e., occipital and parietal) serving distinct functional roles (e.g., Chaumon & Busch, 2014;Gulbinaite, van Viegen, Wieling, Cohen, & VanRullen, 2017;Sokoliuk et al, 2018). Theta appears to be related to attentional sampling (for a review, see VanRullen, 2016).…”

Dissociable electrophysiological correlates of semantic access of motor and non-motor concepts

“…We focused our analyses on the specific anatomical regions identified in the meta-analysis of Watson et al (2013) 33 described in the introduction to this manuscript, and bilateral precentral gyri based on evidence from literature [7][8][9][10][11] . The resulting seven anatomical regions of interest (see Table 2 and Figure 3 for anatomical details) were defined using the automated anatomical labelling (AAL) atlas (see 55,56 for similar analyses with MEG and EEG data). One of these seven AAL regions, the left middle temporal gyrus (left MTG) was further subdivided into anterior (aMTG) and posterior middle temporal gyrus (pMTG) since only the left pMTG was of interest in this study (cf.…”