Cognitive Neuroscience Section, IRCCS Istituto Centro San Giovanni di Dio Fatebenefratelli, Brescia, Italy.
Department of Psychology, University of Milano-Bicocca, Milan, Italy.
Brain Topogr. 2019 Sep;32(5):773-782. doi: 10.1007/s10548-019-00715-x. Epub 2019 May 10.
Existing literature on sensory deprivation suggests that short-lasting periods of dark adaptation (DA) can cause changes in visual cortex excitability. DA cortical effects have previously been assessed through phosphene perception, i.e., the ability to report visual sensations when a transcranial magnetic stimulation (TMS) pulse is delivered over the visual cortex. However, phosphenes represent an indirect measure of visual cortical excitability which relies on a subjective report. Here, we aimed at overcoming this limitation by assessing visual cortical excitability by combining subjective (i.e., TMS-induced phosphenes) and objective (i.e., TMS-evoked potentials - TEPs) measurements in a TMS-EEG protocol after 30 min of DA. DA effects were compared to a control condition, entailing 30 min of controlled light exposure. TMS was applied at 11 intensities in order to estimate the psychometric function of phosphene report and explore the relationship between TEPs and TMS intensity. Compared to light adaptation, after DA the slope of the psychometric function was significantly steeper, and the amplitude of a TEP component (P60) was lower, only for high TMS intensities. The perceptual threshold was not affected by DA. These results support the idea that DA leads to a change in the excitability of the visual cortex, accompanied by a behavioral modification of visual perception. Furthermore, this study provides a first valuable description of the relationship between TMS intensity and visual TEPs.
现有关于感觉剥夺的文献表明，短暂的暗适应（DA）期可能会引起视觉皮层兴奋性的变化。以前，通过闪光感觉（即当经颅磁刺激（TMS）脉冲施加于视觉皮层时能够报告视觉感觉的能力）来评估 DA 对皮层的影响。然而，闪光感觉代表了对视觉皮层兴奋性的间接测量，这种测量依赖于主观报告。在这里，我们旨在通过在 30 分钟的 DA 后结合 TMS-EEG 方案中的主观（即 TMS 诱导的闪光感觉）和客观（即 TMS 诱发的脑电位-TEPS）测量来克服这一局限性，来评估视觉皮层兴奋性。将 DA 效应与对照条件（包括 30 分钟的受控光照暴露）进行了比较。为了估计闪光感觉报告的心理测量函数并探索 TEPs 与 TMS 强度之间的关系，TMS 以 11 种强度施加。与光适应相比，DA 后，闪光感觉报告的心理测量函数的斜率明显陡峭，并且仅对于高 TMS 强度，TEP 成分（P60）的振幅较低。感知阈值不受 DA 的影响。这些结果支持这样的观点，即 DA 导致视觉皮层兴奋性发生变化，并伴有视觉感知的行为改变。此外，这项研究首次提供了 TMS 强度与视觉 TEPs 之间关系的有价值描述。
