Electrical stimulation over the parietal cortex induces spatial bias by mediating the influence of visuospatial attention on the temporal dynamics of visuocortical processing

Previous research suggests that electrical stimulation over posterior parietal cortex (PPC) can modulate visual cognition that requires selective attention,
yet the specific neural processes affected remain unclear. We hypothesized that tDCS over the PPC influenced the distribution of visuospatial attention by
mediating the way selective attention wrap visuocortical processing. We tested this hypothesis using unilateral transcranial direct-current stimulation
(tDCS) to the PPC of male and female human volunteers before we recorded electroencephalography (EEG) and collected psychophysical data. Subjects
performed two different visual tasks, in which they fixated at the central fixation at the fovea and attended to the visual stimuli presented in the periphery
after undergoing a sham procedure on one day and on the other day left or right PPC tDCS, delivered using a double-blind procedure. After active or sham
stimulation, participants completed the attend-fixation or attend-stimulus tasks while we recorded their EEG. Behaviorally, active stimulation led to
asymmetrical psychophysical contrast thresholds, indicating a shift in attention contralateral to the stimulated hemisphere. Electrophysiological findings
supported this, revealing enhanced attentional modulations of early visually evoked responses (P1 component) on the contralateral visual hemisphere.
However, tDCS had no significant effects on attentional modulations of other neural indexes, such as late sustained negative potentials, alpha band
oscillations, and steady-state visually evoked potentials. Our results demonstrate that PPC tDCS alters the spatial distribution of attention by modulating
the temporal dynamics visuocortical activity, providing insight into the neural mechanisms of tDCS-induced modulations of visuospatial attention across
time.