Neural basis of higher visual cognition by using brain models

目的：利用脑模型研究高级视觉认知的神经基础。以阿尔茨海默病（AD）和轻度认知障碍（MCI）患者为疾病模型，采用低频重复经颅磁刺激（rTMS）在健康受试者脑内制造虚拟病变。受试者被要求完成认知任务，如面部识别和连贯运动。在受试者执行认知任务时，评估心理物理和神经生理检查（视觉事件相关电位（ERPs）、脑磁图（MEG）和功能磁共振成像（fMRI））。结果：观察到一些新的发现。首先，我们滤除原始灰度人脸的低或高空间频率成分（宽带空间频率），从而得到粗（低空间频率）和细（高空间频率）人脸。在运动知觉方面，采用相干水平和光流刺激。其次，年龄对运动知觉有明显的影响。有趣的是，MCI和AD均表现出运动阈值升高，MCI表现出光流运动敏感性降低。第三，记录erp与面部和运动感知的地形映射。在人脸任务中，枕部P1表现出对人脸的整体处理。颞枕部的N170反映了面部识别。后期慢速成分（N250-400）对面部表情表现出明显的敏感性。首先区分积极和消极表达的差异，然后区分消极表达。P200指示光流知觉，在轻度认知损伤患者中延迟或缺失。目前，我们正在记录面部和运动感知过程中的MEG和fMRI，以进一步研究神经机制。最后，在健康受试者的V1和V5上应用低频rTMS，使运动知觉的反应时间增加，这种效果持续40分钟。因此，rTMS是一种很有前途的探索高级视觉认知神经网络的方法。少

OBJECTIVES : We studied the neural basis of higher visual cognitions by using brain models. Low-frequency repetitive transcranial magnetic stimulation (rTMS) was used to produce brain virtual lesion in healthy subjects while patients with Alzheimer disease (AD) and mild cognitive impairment (MCI) were considered as disease models. Subjects were instructed to perform cognitive tasks such as face recognition and coherent motion. Psychophysical and neurophysiological examinations (visual event-related potentials (ERPs), magnetoencehalography (MEG) and functional magnetic resonance imaging (fMRI)) were evaluated while the subjects performed cognitive tasks.RESULTS : Several new findings were observed. First, we filtered out either low or high spatial frequency components of the original grayscale faces (broadband spatial frequency) so that coarse (low spatial frequency) and fine (high spatial frequency) faces were made. For motion perception, coherent horizontal and optic flow stimuli were … More employed. Second, aging has a distinct effect on the motion perception. Interestingly, both MCI and AD showed increased motion thresholds and MCI revealed decreased sensitivity for optic flow motion. Third, topographical mapping of ERPs to face and motion perception was recorded. In the face tasks, P1 at the occipital site showed holistic processing of faces. N170 at the temporooccipital site reflects facial identification. Late slow components (N250-400) show distinct sensitivities for facial expressions. The difference between positive and negative expressions was first discriminated, then discrimination of negative expressions was achieved. P200 is indicative of optic flow perception and was delayed or absent in patients with MCI. Currently, we are recording MEG and fMRI during face and motion perception to further investigate the neural mechanisms. Finally, low-frequency rTMS was applied over V1 and V5 in healthy subjects, which resulted in increased reaction times for motion perception and this effect lasted for 40 min. Therefore, rTMS is a promising method for exploring the neural network for higher visual cognition. Less