Parietal alpha stimulation causally enhances attentional information coding in evoked and oscillatory activity

Lu, Runhao; Michael, Elizabeth; Scrivener, Catriona L.; Jackson, Jade B.; Duncan, John; Woolgar, Alexandra · 2023 · Crossref

DOI: 10.1101/2023.11.14.567111

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Summary

This study investigates the causal roles of parietal evoked potentials and alpha oscillations in coding specific aspects of selective attention: spatial location (where to attend), task rules (what to attend to), and visual features. While previous research established correlational links between these neural signals and attention, the specific informational content and causal influence of each signal type remained unclear. The authors employed concurrent transcranial magnetic stimulation and electroencephalography (TMS-EEG) to manipulate right intraparietal sulcus (IPS) activity and assess its downstream effects on neural coding and behavior. The experimental design consisted of two parts. First, using EEG-only data, the researchers applied time-resolved multivariate pattern analysis (MVPA) to decode task-relevant information from evoked potentials (1–6 Hz) and alpha power (8–13 Hz). Second, they applied rhythmic TMS (rTMS) at individual alpha frequencies over the right IPS, compared against control arrhythmic TMS (aTMS), to causally entrain alpha activity. Participants performed a selective attention task requiring them to attend to specific locations and features (color or orientation) of visual stimuli. In the EEG-only phase, results indicated functional dissociations: evoked potentials coded all three task aspects (location, rule, and feature) with distinct temporal dynamics, whereas alpha oscillations carried information only about location and task rules, but not visual features. Feature coding in evoked potentials supported an object-based attention hypothesis, prioritizing all features of the attended object regardless of task relevance. In the TMS-EEG phase, alpha rTMS successfully increased alpha power and inter-trial phase coherence compared to aTMS. Crucially, rTMS causally enhanced the multivariate decoding of spatial location information ("where to attend") in both evoked potentials and alpha oscillations. This enhancement was specific; rTMS did not improve decoding of task rules or visual features. Furthermore, rTMS increased the amplitude of posterior-contralateral evoked potentials, indicating greater attentional resource allocation. The significance of these findings lies in establishing a specific causal link between IPS-controlled alpha activity and the neural coding of spatial attention. The study demonstrates that enhancing parietal alpha oscillations specifically improves the brain's ability to encode spatial location information, which in turn predicts improvements in behavioral performance. This clarifies the complementary roles of evoked potentials and alpha oscillations, showing that while evoked potentials broadly encode multiple task elements, alpha oscillations play a specialized, causal role in driving the coding of spatial attention.

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