The Wellcome Centre for Human Neuroimaging, UCL Queen Square Institute of Neurology, University College London, London WC1N 3AR, UK.
Department of Neurobiology, Weizmann Institute of Science, Rehovot, 7610001, Israel.
Brain. 2021 Feb 12;144(1):340-353. doi: 10.1093/brain/awaa384.
Spontaneous activity of the human brain has been well documented, but little is known about the functional role of this ubiquitous neural phenomenon. It has previously been hypothesized that spontaneous brain activity underlies unprompted (internally generated) behaviour. We tested whether spontaneous brain activity might underlie internally-generated vision by studying the cortical visual system of five blind/visually-impaired individuals who experience vivid visual hallucinations (Charles Bonnet syndrome). Neural populations in the visual system of these individuals are deprived of external input, which may lead to their hyper-sensitization to spontaneous activity fluctuations. To test whether these spontaneous fluctuations can subserve visual hallucinations, the functional MRI brain activity of participants with Charles Bonnet syndrome obtained while they reported their hallucinations (spontaneous internally-generated vision) was compared to the: (i) brain activity evoked by veridical vision (externally-triggered vision) in sighted controls who were presented with a visual simulation of the hallucinatory streams; and (ii) brain activity of non-hallucinating blind controls during visual imagery (cued internally-generated vision). All conditions showed activity spanning large portions of the visual system. However, only the hallucination condition in the Charles Bonnet syndrome participants demonstrated unique temporal dynamics, characterized by a slow build-up of neural activity prior to the reported onset of hallucinations. This build-up was most pronounced in early visual cortex and then decayed along the visual hierarchy. These results suggest that, in the absence of external visual input, a build-up of spontaneous fluctuations in early visual cortex may activate the visual hierarchy, thereby triggering the experience of vision.
人类大脑的自发性活动已有充分记录，但对于这种普遍存在的神经现象的功能作用知之甚少。先前有人假设，自发性大脑活动是自发（内部产生）行为的基础。我们通过研究 5 名失明/视力受损个体的皮质视觉系统来测试自发性大脑活动是否可能是内部产生视觉的基础，这些个体患有生动的视觉幻觉（Charles Bonnet 综合征）。这些个体的视觉系统中的神经群体被剥夺了外部输入，这可能导致它们对自发性活动波动的超敏反应。为了测试这些自发性波动是否可以服务于视觉幻觉，我们比较了 Charles Bonnet 综合征患者在报告幻觉时（自发的内部产生的视觉）的功能磁共振成像脑活动与：（i）视力正常的对照者在观看视觉模拟幻觉流时引发的脑活动（外部触发的视觉）；以及（ii）非幻觉性失明对照者在进行视觉想象时（内部 cue 产生的视觉）的脑活动。所有条件都显示了跨越视觉系统大部分区域的活动。然而，只有 Charles Bonnet 综合征患者的幻觉条件表现出独特的时间动态，其特征是在报告幻觉发作之前，神经活动缓慢增加。这种增加在早期视觉皮层最为明显，然后沿着视觉层次结构衰减。这些结果表明，在没有外部视觉输入的情况下，早期视觉皮层中自发性波动的增加可能会激活视觉层次结构，从而触发视觉体验。
