Arshad Q, Siddiqui S, Ramachandran S, Goga U, Bonsu A, Patel M, Roberts R E, Nigmatullina Y, Malhotra P, Bronstein A M
Division of Brain Sciences, Charing Cross Hospital Campus, Imperial College, Fulham Palace Road, London W6 8RF, UK.
Division of Brain Sciences, Charing Cross Hospital Campus, Imperial College, Fulham Palace Road, London W6 8RF, UK.
Neuroscience. 2015 Dec 17;311:484-9. doi: 10.1016/j.neuroscience.2015.10.045. Epub 2015 Oct 27.
Right hemisphere dominance for visuo-spatial attention is characteristically observed in most right-handed individuals. This dominance has been attributed to both an anatomically larger right fronto-parietal network and the existence of asymmetric parietal interhemispheric connections. Previously it has been demonstrated that interhemispheric conflict, which induces left hemisphere inhibition, results in the modulation of both (i) the excitability of the early visual cortex (V1) and (ii) the brainstem-mediated vestibular-ocular reflex (VOR) via top-down control mechanisms. However to date, it remains unknown whether the degree of an individual's right hemisphere dominance for visuospatial function can influence, (i) the baseline excitability of the visual cortex and (ii) the extent to which the right hemisphere can exert top-down modulation. We directly tested this by correlating line bisection error (or pseudoneglect), taken as a measure of right hemisphere dominance, with both (i) visual cortical excitability measured using phosphene perception elicited via single-pulse occipital trans-cranial magnetic stimulation (TMS) and (ii) the degree of trans-cranial direct current stimulation (tDCS)-mediated VOR suppression, following left hemisphere inhibition. We found that those individuals with greater right hemisphere dominance had a less excitable early visual cortex at baseline and demonstrated a greater degree of vestibular nystagmus suppression following left hemisphere cathodal tDCS. To conclude, our results provide the first demonstration that individual differences in right hemisphere dominance can directly predict both the baseline excitability of low-level brain structures and the degree of top-down modulation exerted over them.
在大多数右利手个体中，通常可以观察到右半球在视觉空间注意力方面占主导地位。这种主导地位既归因于解剖学上更大的右额顶叶网络，也归因于不对称的顶叶半球间连接的存在。此前已经证明，诱导左半球抑制的半球间冲突会通过自上而下的控制机制，对（i）早期视觉皮层（V1）的兴奋性和（ii）脑干介导的前庭眼反射（VOR）产生调节作用。然而，迄今为止，尚不清楚个体右半球在视觉空间功能方面的主导程度是否会影响（i）视觉皮层的基线兴奋性，以及（ii）右半球能够施加自上而下调节的程度。我们通过将作为右半球主导程度衡量指标的直线二等分误差（或假性忽视），与（i）通过单脉冲枕部经颅磁刺激（TMS）诱发的光幻视感知所测量的视觉皮层兴奋性，以及（ii）在左半球抑制后经颅直流电刺激（tDCS）介导的VOR抑制程度进行关联，直接对此进行了测试。我们发现，那些右半球主导程度较高的个体，其早期视觉皮层在基线时兴奋性较低，并且在左半球阴极tDCS后表现出更大程度的前庭眼震抑制。总之，我们的结果首次证明了右半球主导程度的个体差异可以直接预测低级脑结构的基线兴奋性以及对其施加的自上而下调节的程度。
