Cazzoli Dario, Wurtz Pascal, Müri René M, Hess Christian W, Nyffeler Thomas
Perception and Eye Movement Laboratory, Department of Neurology, Bern University Hospital Inselspital, and University of Bern, Bern, Switzerland.
Eur J Neurosci. 2009 Mar;29(6):1271-6. doi: 10.1111/j.1460-9568.2009.06665.x.
Interhemispheric imbalance is discussed as a pathophysiological mechanism in visuospatial neglect. It is suggested that after a lesion of the right hemisphere the mutual transcallosal inhibition is impaired, resulting in an increased activity of the left hemisphere. We investigated the interhemispheric balance of attention in healthy subjects by using a free visual exploration task and by interfering with the neural activity of the posterior parietal cortex (PPC) of either hemisphere using an inhibitory transcranial magnetic stimulation routine with theta burst stimulation (TBS). Subjects explored colour photographs of real-life scenes presented on a computer screen under four conditions: (i) without TBS; (ii) after TBS over the right PPC; (iii) after TBS over the left PPC; and (iv) after TBS over the right PPC and, after the first half of the task, over the left PPC. Eye movements were measured, and distribution of mean cumulative fixation duration over screen halves was analyzed. TBS over the right PPC resulted in a significant rightward shift of mean cumulative fixation duration of approximately 30 min. The shift could be reversed when a subsequent train of TBS was applied over the left PPC. However, left PPC stimulation alone had no significant effect on visual exploration behaviour. The present study shows that the effect of TBS on the PPC depends on which hemisphere is stimulated and on the state of the contralateral homologue area. These findings are in accordance with the predictions of the interhemispheric rivalry model in neglect.
半球间失衡被认为是视觉空间忽视的一种病理生理机制。有人提出，在右侧半球受损后，胼胝体间的相互抑制会受到损害，导致左侧半球活动增加。我们通过使用自由视觉探索任务，并使用带有theta爆发刺激（TBS）的抑制性经颅磁刺激程序干扰任一半球的后顶叶皮质（PPC）的神经活动，来研究健康受试者的半球间注意力平衡。受试者在四种条件下探索电脑屏幕上呈现的现实生活场景的彩色照片：（i）无TBS；（ii）右侧PPC进行TBS后；（iii）左侧PPC进行TBS后；（iv）右侧PPC进行TBS后，且在任务的前半部分之后，左侧PPC进行TBS。测量眼动，并分析平均累积注视持续时间在屏幕两半的分布。右侧PPC进行TBS导致平均累积注视持续时间显著向右偏移约30分钟。当随后在左侧PPC施加一系列TBS时，这种偏移可以被逆转。然而，单独刺激左侧PPC对视觉探索行为没有显著影响。本研究表明，TBS对PPC的影响取决于刺激的是哪个半球以及对侧同源区域的状态。这些发现与忽视中半球间竞争模型的预测一致。
