Influences of right parietal cortex in the visual processing of contralateral visual stimuli in a sustained attentional context

Visuospatial attention is essential for successful interactions with the environment. It has been shown that visuospatial attention is based on a right lateralized network of parietal and frontal areas. Indeed, insights about this network arise from studies with visual neglect patients, who after a localized lesion in right parietal or temporal areas fail to perceive or attend normally to signals in the contralateral left visual hemifield. Accumulating evidence shows that transcranial magnetic stimulation (TMS) over the parietal cortex is able to induce neglect-like changes in performance during visuopatial tasks. At the neural level, parietal TMS has also been shown to modulate activity in remote interconnected areas of the brain, in particular in the occipito-temporal cortex. This study used concurrent TMS-fMRI to investigate the role of the right intraparietal sulcus (IPS) in visual detection under spatial attention. Participants performed a visual target detection task during TMS-stimulation to the right anterior IPS and Sham-TMS-stimulation where specific TMS effects were abolished by placing a 2cm thick plastic plate between the TMS-coil and the participant's head. In both conditions, TMS was applied in bursts of 4 pulses (10Hz), starting 90ms after the target onset. Participants fixated on a cross in the centre of the screen and attended to a location indicated by a placeholder in the left lower visual field. On each trial, they indicated whether they detected a small visual stimulus that was presented inside the placeholder on 50 of the trials. Blocks of 12 trials were interleaved with baseline periods of 13s. Hence, attention was sustained specifically to the left visual field throughout the entire block relative to baseline. As expected, compared to baseline, attended periods activated the network of fronto-parietal areas commonly involved in attention. Critically, IPS-TMS relative to Sham-TMS significantly decreased the difference in activations between visual present and visual absent trials by reducing the deactivations during visual present trials in the right anterior fusiform gyrus, an area that has previously been reported to be modulated by attention. Our results show that the right human parietal cortex influences visual processing in the right ipsilateral occipital cortex by modulating stimulus evoked (de)activations during spatial attention