Rina Andriani, Papanikolaou Amalia, Zong Xiaopeng, Papageorgiou Dorina T, Keliris Georgios A, Smirnakis Stelios M
Department of Neurology Brigham and Women's Hospital and Jamaica Plain Veterans Administration Hospital, Harvard Medical School, Boston, MA, United States.
Visual and Cognitive Neuroscience, Faculty of Science, University of Tübingen, Tuebingen, Germany.
Front Neurosci. 2022 Mar 2;16:719250. doi: 10.3389/fnins.2022.719250. eCollection 2022.
Random dot kinematograms (RDKs) have recently been used to train subjects with cortical scotomas to perform direction of motion discrimination, partially restoring visual motion perception. To study the recovery of visual perception, it is important to understand how visual areas in normal subjects and subjects with cortical scotomas respond to RDK stimuli. Studies in normal subjects have shown that blood oxygen level-dependent (BOLD) responses in human area hV5/MT+ increase monotonically with coherence, in general agreement with electrophysiology studies in primates. However, RDK responses in prior studies were obtained while the subject was performing fixation, not a motion discrimination condition. Furthermore, BOLD responses were gauged against a baseline condition of uniform illumination or static dots, potentially decreasing the specificity of responses for the spatial integration of local motion signals (motion coherence). Here, we revisit this question starting from a baseline RDK condition of no coherence, thereby isolating the component of BOLD response due specifically to the spatial integration of local motion signals. In agreement with prior studies, we found that responses in the area hV5/MT+ of healthy subjects were monotonically increasing when subjects fixated without performing a motion discrimination task. In contrast, when subjects were performing an RDK direction of motion discrimination task, responses in the area hV5/MT+ remained flat, changing minimally, if at all, as a function of motion coherence. A similar pattern of responses was seen in the area hV5/MT+ of subjects with dense cortical scotomas performing direction of motion discrimination for RDKs presented inside the scotoma. Passive RDK presentation within the scotoma elicited no significant hV5/MT+ responses. These observations shed further light on how visual cortex responses behave as a function of motion coherence, helping to prepare the ground for future studies using these methods to study visual system recovery after injury.
随机点运动图（RDKs）最近已被用于训练患有皮质性暗点的受试者进行运动方向辨别，从而部分恢复视觉运动感知。为了研究视觉感知的恢复情况，了解正常受试者和患有皮质性暗点的受试者的视觉区域如何对RDK刺激做出反应非常重要。对正常受试者的研究表明，人类hV5/MT+区域的血氧水平依赖性（BOLD）反应通常与灵长类动物的电生理学研究一致，随连贯性单调增加。然而，先前研究中的RDK反应是在受试者进行注视时获得的，而不是在运动辨别条件下。此外，BOLD反应是根据均匀照明或静态点的基线条件来衡量的，这可能会降低对局部运动信号空间整合（运动连贯性）反应的特异性。在这里，我们从无连贯性的基线RDK条件开始重新审视这个问题，从而分离出专门由于局部运动信号空间整合而产生的BOLD反应成分。与先前的研究一致，我们发现，当健康受试者在不执行运动辨别任务的情况下进行注视时，hV5/MT+区域的反应呈单调增加。相比之下，当受试者执行RDK运动方向辨别任务时，hV5/MT+区域的反应保持平稳，随运动连贯性的变化极小（如果有变化的话）。在患有密集皮质性暗点的受试者中进行暗点内呈现的RDK运动方向辨别时，hV5/MT+区域也出现了类似的反应模式。在暗点内被动呈现RDK不会引起显著的hV5/MT+反应。这些观察结果进一步揭示了视觉皮层反应如何随运动连贯性而变化，有助于为未来使用这些方法研究损伤后视觉系统恢复的研究奠定基础。
