The role of the parietal lobe in task-irrelevant suppression during learning

BackgroundAttention optimizes the selection of visual information, while suppressing irrelevant visual input through cortical mechanisms that are still unclear. We set to investigate these processes using an attention task with an embedded to-be-ignored interfering visual input. ObjectiveWe delivered electrical stimulation to attention-related brain areas to modulate these facilitatory/inhibitory attentional mechanisms. We asked whether training on a task while being simultaneously exposed to visual features from a different task tested at baseline and post-training might influence performance on the baseline task. MethodsIn Experiment one, subjects performed an orientation discrimination (OD) task using a pair of gratings presented at individuals psychophysical threshold. We then trained participants over multiple sessions on a temporal order judgment task (TOJ), using the exact same gratings but presented with different time offsets. On the last session we re-tested OD. We coupled training with transcranial random noise stimulation (tRNS) over the parietal cortex, the human middle temporal area or sham, in three separate groups. In Experiment two, subjects performed the same OD task at baseline and post-training, while tRNS was delivered at rest during training. ResultsResults showed that tRNS over parietal cortex facilitated learning of the trained task. Moreover, we found a detrimental effect on OD when subjects received parietal tRNS coupled with training, but a benefit on OD when subjects received stimulation while at rest. ConclusionsThese results clearly indicate that task-irrelevant information is actively suppressed during learning, and that this prioritization mechanism of selection likely resides in the parietal cortex.