A Research On Visual Fronto-parietal Attention Network Based On TMS And FMRI

Visual attention is one of the most fundamental cognitive activity in human.It plays an very important role in the process of visual information processing and visual percep-tion and It can improve the detection ability of behavior and shorten the reaction.Visual at-tention is controlled by both top-down cognitive and bottom-up sensory factors.A variety of neuroimaging studies provide compelling evdence that frontoparietal network centered on the frontal and parietal lobes play very important roles in both types attention control.But how do those regions of frontoparietal network modulated with each other and how those brain areas connect and communicative with each other to deal with different kind of attention tasks?All those questions need a more in-depth and thorough research on the frontoparietal attention network.In this study,functional magnetic resonance imaging?fMRI?and transcranial mag-netic stimulation?TMS?were used to explore the visual attention frontal network.In order to trigger different attention control mechanisms,we use the visual search paradigm in the previous study.The paradigm contains two types of stimuli tasks:pop-out and search.In the pop-out condition the distractors differed from the target in both orientation and color,such that the target drew attention automatically.Whereas in the search condition the target differed from the distractors only in orientation,so that the search required more effort.The whole brain under the pop-out task and search task was scanned by fMRI to analyze the activation of the brain regions under the two task conditions,and three re-gions of interest?ROI?including dorsolateral prefrontal cortex?DLPFC?,frontal eye field?FEF?,superior parietal lobule?SPL?of the right hemisphere was selected based on the results of previous studies to conduct the follow-up TMS experiment.The behavior per-formance of participants were recorded during the TMS stimulation process to perform a more in-depth and detailed analysis.The behavior performance of both fRMI and TMS indicate that there are significant differences in the accuracy and average reaction time under the two visual search tasks,in-dicating that the two tasks belong to two different difficulty levels,but also suggesting that the information transfer process separately triggers different attention control mechanisms via different paths.It also illustrates the validity of this experimental paradigm.The fMRI results showed that the bottom-up attention modulation mainly activated the frontal,parietal,temporal,and limbic lobes,and the top-down attention modulation mainly activated the frontal,occipital,parietal,and bilateral Insula.And the pop-out task activates the parietal lobe more,and the search task activates more frontal lobes.This is consistent with our previous ERP experiment^[1].In addition,the anterior and the posterior of the cingulate are involved in different attention control mechanisms while the anterior cingulate cortex participates in the top-down attention process,and the posterior cingulate cortex takes part in the bottom-up attention process.The TMS results suggest that TMS stimulation to the right DLPFC,FEF,SPL will inhibit the behavior performance under the search task,and the SPL inhibition is more intense than DLPFC,FEF,and TMS stimulation only has an inhibitory effect on SPL under pop-out task.In addition,we used this group of brain regions to perform ROI analysis on the above fMRI data and found that regardless of the task,the percent singal change of the SPL region is the strongest among the three brain regions,followed by the FEF region,where DLPFC is weakest.And the percent signal change of the search task are bigger than the pop-out task.Therefore,it shows that DLPFC and FEF participate in the top-down attention control process,and SPL plays an important role in both bottom-up and top-down attention control.Both tasks in our experiment,the results of specific stimulation to multiple sites con-sistently showed that the stimulation of the visual search task by the rTMS will result in“virtual damage”of the brain function and interfere with the performance of the search task.