Laboratory for Human Brain Dynamics, AAI Scientific Cultural Services Ltd. Nicosia, Cyprus.
Front Hum Neurosci. 2013 Aug 5;7:429. doi: 10.3389/fnhum.2013.00429. eCollection 2013.
Cross-modal activity in visual cortex of blind subjects has been reported during performance of variety of non-visual tasks. A key unanswered question is through which pathways non-visual inputs are funneled to the visual cortex. Here we used tomographic analysis of single trial magnetoencephalography (MEG) data recorded from one congenitally blind and two sighted subjects after stimulation of the left and right median nerves at three intensities: below sensory threshold, above sensory threshold and above motor threshold; the last sufficient to produce thumb twitching. We identified reproducible brain responses in the primary somatosensory (S1) and motor (M1) cortices at around 20 ms post-stimulus, which were very similar in sighted and blind subjects. Time-frequency analysis revealed strong 45-70 Hz activity at latencies of 20-50 ms in S1 and M1, and posterior parietal cortex Brodmann areas (BA) 7 and 40, which compared to lower frequencies, were substantially more pronounced in the blind than the sighted subjects. Critically, at frequencies from α-band up to 100 Hz we found clear, strong, and widespread responses in the visual cortex of the blind subject, which increased with the intensity of the somatosensory stimuli. Time-delayed mutual information (MI) revealed that in blind subject the stimulus information is funneled from the early somatosensory to visual cortex through posterior parietal BA 7 and 40, projecting first to visual areas V5 and V3, and eventually V1. The flow of information through this pathway occurred in stages characterized by convergence of activations into specific cortical regions. In sighted subjects, no linked activity was found that led from the somatosensory to the visual cortex through any of the studied brain regions. These results provide the first evidence from MEG that in blind subjects, tactile information is routed from primary somatosensory to occipital cortex via the posterior parietal cortex.
盲人群体在执行各种非视觉任务时，其视觉皮层会出现跨模态活动。一个尚未解决的关键问题是，非视觉输入是通过哪些途径传入视觉皮层的。在这里，我们使用单试磁共振脑磁图（MEG）数据的层析分析，对一名先天性失明和两名视力正常的受试者进行了研究，这些数据是在刺激左、右正中神经时记录的，刺激强度分为三种：低于感觉阈、高于感觉阈和高于运动阈；最后一种强度足以引起拇指抽搐。我们在刺激后约 20 毫秒时，在初级体感（S1）和运动（M1）皮层中识别到了可重复的大脑反应，在视力正常和失明的受试者中，这些反应非常相似。时频分析显示，在 S1 和 M1 以及顶后皮质 Brodmann 区（BA）7 和 40 的潜伏期为 20-50 毫秒处，存在强烈的 45-70 Hz 活动，与低频相比，在失明受试者中比视力正常受试者更为明显。重要的是，在α频段到 100 Hz 的频率范围内，我们在失明受试者的视觉皮层中发现了清晰、强烈和广泛的反应，这些反应随着体感刺激的强度而增加。时滞互信息（MI）显示，在失明受试者中，刺激信息通过顶后皮质 BA7 和 40 从早期体感传入视觉皮层，最初投射到 V5 和 V3 区，最终投射到 V1 区。信息通过该途径的流动分阶段进行，特征是激活在特定的皮层区域汇聚。在视力正常的受试者中，没有发现从体感到视觉皮层的任何连接活动，这些活动通过任何研究中的大脑区域进行。这些结果首次从 MEG 中提供了证据，表明在失明受试者中，触觉信息是通过顶后皮质从初级体感传入枕叶皮层的。
