Lu, R.; Michael, E.; Scrivener, C. L.; Jackson, J. B.; Duncan, J.; Woolgar, A.

Selective attention is a fundamental cognitive mechanism that allows people to prioritise task-relevant information while ignoring irrelevant information. Previous research has suggested key roles of parietal evoked potentials like N2pc, and parietal oscillatory responses like alpha power, in spatial attention tasks. However, the informational content of these signals is less clear. Spatial attention tasks require not only representation of spatial information (i.e., where to attend) but also task (e.g., what to attend to) and visual feature information (e.g., details of visual stimuli). Whether all these features are represented in both evoked and oscillatory responses, and with what dynamics, is unknown. Moreover, the question of whether parietal evoked potentials and/or alpha power causally influence the coding of these different task elements is yet unresolved. Here, we used concurrent TMS-EEG to causally manipulate parietal alpha power and evoked potentials and investigate their roles in coding task-relevant information in a selective attention task. First, using EEG-only data, we investigated the decodability and temporal dynamics of evoked potentials and alpha power in coding different aspects of a selective attention task (where to attend, what to attend to, and visual feature information). We found that evoked potentials coded all three types of task-relevant information with distinct temporal dynamics, and alpha oscillations carried information regarding both where to attend and what to attend to. Then, we applied rhythmic-TMS (rTMS) at individual alpha frequency over the right intraparietal sulcus (IPS), to examine the causal roles of evoked potentials and alpha oscillations in selective attention. Compared with the control arrhythmic-TMS, alpha rTMS increased power and inter-trial phase coherence in alpha band and induced more negative N2pc amplitudes. Moreover, alpha rTMS causally and specifically improved multivariate decoding accuracy of the information about where to attend but not what to attend to or feature information during task performance. This TMS-induced change in decoding information about where to attend, encoded in both evoked potentials and alpha power, predicted TMS-induced changes in response errors and reaction time. These findings illuminate the dynamics with which the complementary aspects of a selective attention task are encoded in evoked and oscillatory brain activity. Moreover, they reveal a specific and causal role of IPS-controlled evoked and oscillatory activity in carrying behaviour-driving information about where to focus attention.