Behrens Janina R, Kraft Antje, Irlbacher Kerstin, Gerhardt Holger, Olma Manuel C, Brandt Stephan A
Charité Universitätsmedizin BerlinBerlin, Germany.
NeuroCare Clinical Research Center, Charité Universitätsmedizin BerlinBerlin, Germany.
Front Cell Neurosci. 2017 Aug 15;11:238. doi: 10.3389/fncel.2017.00238. eCollection 2017.
Understanding processes performed by an intact visual cortex as the basis for developing methods that enhance or restore visual perception is of great interest to both researchers and medical practitioners. Here, we explore whether contrast sensitivity, a main function of the primary visual cortex (V1), can be improved in healthy subjects by repetitive, noninvasive anodal transcranial direct current stimulation (tDCS). Contrast perception was measured via threshold perimetry directly before and after intervention (tDCS or sham stimulation) on each day over 5 consecutive days (24 subjects, double-blind study). tDCS improved contrast sensitivity from the second day onwards, with significant effects lasting 24 h. After the last stimulation on day 5, the anodal group showed a significantly greater improvement in contrast perception than the sham group (23 vs. 5%). We found significant long-term effects in only the central 2-4° of the visual field 4 weeks after the last stimulation. We suspect a combination of two factors contributes to these lasting effects. First, the V1 area that represents the central retina was located closer to the polarization electrode, resulting in higher current density. Second, the central visual field is represented by a larger cortical area relative to the peripheral visual field (cortical magnification). This is the first study showing that tDCS over V1 enhances contrast perception in healthy subjects for several weeks. This study contributes to the investigation of the causal relationship between the external modulation of neuronal membrane potential and behavior (in our case, visual perception). Because the vast majority of human studies only show temporary effects after single tDCS sessions targeting the visual system, our study underpins the potential for lasting effects of repetitive tDCS-induced modulation of neuronal excitability.
理解完整视觉皮层所执行的过程，以此为基础开发增强或恢复视觉感知的方法，这对研究人员和医学从业者都极具吸引力。在此，我们探究初级视觉皮层（V1）的主要功能——对比敏感度，能否通过重复性、非侵入性阳极经颅直流电刺激（tDCS）在健康受试者中得到改善。在连续5天的每一天，于干预（tDCS或假刺激）前后，通过阈值视野检查法测量对比感知（24名受试者，双盲研究）。从第二天起，tDCS改善了对比敏感度，显著效果持续24小时。在第5天最后一次刺激后，阳极组在对比感知方面的改善显著大于假刺激组（23%对5%）。在最后一次刺激4周后，我们仅在视野中央2 - 4°发现了显著的长期效应。我们怀疑有两个因素共同导致了这些持久效应。首先，代表中央视网膜的V1区域更靠近极化电极，导致电流密度更高。其次，相对于周边视野，中央视野由更大的皮质区域所代表（皮质放大）。这是第一项表明对V1进行tDCS可在数周内增强健康受试者对比感知的研究。本研究有助于探究神经元膜电位的外部调制与行为（在我们的案例中为视觉感知）之间的因果关系。由于绝大多数人体研究仅显示在针对视觉系统的单次tDCS治疗后有暂时效应，我们的研究支持了重复性tDCS诱导的神经元兴奋性调制具有持久效应的可能性。
