Neural correlates of spatial attention bias: Changes in functional connectivity in attention networks associated with tDCS

The prevailing theory concerning the pathophysiology of unilateral spatial neglect is that it is caused by an interhemispheric imbalance in attention networks. Previous studies have demonstrated that repetitive transcranial magnetic stimulation or transcranial direct current stimulation (tDCS) delivered over the right posterior parietal cortex can induce transitory neglect-like deficits in healthy individuals. We examined whether right cathodal and left anodal tDCS delivered over the posterior parietal cortex could produce neglect-like deficits and change the resting-state functional connectivity (rsFC) of attention networks. We found that the reaction time for targets in the left hemifield was significantly prolonged during two different types of visual search tasks, and rsFC of the attention networks was altered by tDCS. Furthermore, the change in the reaction times for the left visual target in the two different tasks significantly correlated with the change in the rsFC of either the right dorsal attention network (DAN) or right ventral attention network (VAN) based on the tasks. These results suggest that tDCS delivered to the posterior parietal cortex bilaterally induced neglect-like deficits by altering the connectivity of the attentional networks through excitability changes in the cortical area under the electrode. The results of this study are consistent with the hypothesis that the cause of neglect is the interhemispheric imbalance of attention networks. This is the first study to demonstrate that local cortical stimulation can induce changes not only in the local brain function but also in the cortical networks in healthy individuals.

The precuneus and visuospatial attention in near and far space: a transcranial magnetic stimulation study

BACKGROUND

There is a large body of evidence for the involvement of the parietal cortex in orientation and navigation in space. This has been supplemented by investigation of the contribution of a number of subregions using transcranial magnetic stimulation.

OBJECTIVE

The role of the precuneus area, located in the medial plane of posterior parietal cortex (PPC), in visuospatial functions is not well understood. We investigated the contribution of this area using the landmark task.

METHODS

Participants were asked to make forced-choice judgments of which side of prebisected line was longer for near and far viewing conditions (70 and 180 cm, respectively). Online 10 Hz, repetitive transcranial magnetic stimulation (rTMS) was delivered for 500 ms over the right precuneus, rPPC and vertex (control), in separate blocks of trials. The rPPC stimulation was used as a positive control, having previously resulted in "neglect like" spatial bias effects in a number of studies.

RESULTS

A no-TMS condition showed a leftward spatial bias (pseudoneglect) for near space judgments but not for far space and was used as the baseline. Precuneus stimulation resulted in rightward spatial bias from the midpoint in near space similar to the rPPC neglect-like effect. No significant effects were seen with vertex stimulation.

CONCLUSION

This study shows that precuneus, like other parietal areas, is involved in visuospatial functions. Further work is required to clarify how the contribution of this area differs from other parietal regions.