视觉对比度检测的脑机制研究

There are inconsistent points of view about the contributions of higher order cortical region and early visual cortex to visual perception and perceptual learning. To solve this dispute, this research project plans to examine the dual effects of higher order cortical region of cat on the perceptual ability of visual stimulus contrast detection and the neuronal activities in the primary visual cortex (V1). Transcranial direct current stimulation (tDCS) techniques will be used to modify the excitability of different higher order cortical areas respectively. Before and after tDCS, the contrast threshold that the cats can detect stimuli with different level of external noise interference will be measured with 2-AFC method, so as to construct psychological TvC (contrast threshold versus external noise contrast) curves. The tuning response of V1 neurons to stimuli of different contrast under each level of noise interference was studied before and after tDCS respectively using chronical in vivo single-unit recording techniques. ROC analysis will be used to acquire the stimulus contrast threshold of neuronal response, so as to construct V1 neuronal population TvC curves. By examining the tDCS-induced contrast threshold change at low and high noise portions of TvC curves as well as the change relationship between psychophysical level and V1 neuronal level, we attempt to investigate the relative contribution of different higher order cortical areas and V1 to stimulus contrast detection. This research is of great value in elucidating the brain mechanism of visual perception and perceptual learning and in treating visual impairments related to amblyopia and etc.

高级脑区和初级视区对视知觉及知觉学习的贡献存在意见分歧。为解决争议，本项目研究猫的高级脑区对刺激对比度检测的知觉能力和初级视皮层（V1）神经活动的双重影响。采用经颅直流电刺激（tDCS）分别改变不同高级脑区的兴奋性。在tDCS前、后，用2-AFC方法测试猫对不同外噪声干扰的刺激辨别的对比度阈值，以建立心理学TvC（contrast threshold versus external noise contrast）曲线；用在体单细胞慢性记录技术研究V1细胞对各噪声等级下不同对比度刺激的调谐反应，经ROC分析方法获得细胞对刺激反应的对比度阈值，以建立V1细胞群TvC曲线。通过检测tDCS对TvC曲线的高、低噪声部影响幅度及其在心理学和V1细胞水平的相关性，探讨不同高级脑区和初级视皮层对刺激对比度检测的相对贡献大小。该研究对阐明视知觉和知觉学习的脑机制及治疗弱视等相关视觉缺陷有重要价值。

高级脑区和初级视皮层（V1）对视知觉和知觉学习的贡献存在意见分歧。为解决争议，我们采用经颅直流电刺激（tDCS）改变猫的不同高级脑区的兴奋性，研究高级脑区反馈作用变化对行为学视觉对比度检测能力和V1神经元反应的对比敏感度影响。分别在tDCS前后测试猫对不同空间频率（SF）及不同等级外噪声（external noise）干扰的光栅刺激辨别的对比度阈值（TC），以建立行为学对比敏感度CSF（contrast sensitivity versus SF）及TvC（TC versus external noise contrast）曲线；用电生理慢性记录技术记录V1神经元群对不同SF及不同外噪声水平下的梯度对比度光栅刺激反应的诱发场电位（VEP），经VEP峰-峰值幅度的ROC分析获得神经元群的CSF和TvC曲线。结果发现:（1）阳极（a-）和阴极（c-）tDCS分别能增强和抑制高级脑区的神经活动并持续约60-70 min。（2）高级视区的反馈作用能显著提高V1神经元对刺激反应的对比敏感度，减弱V1神经元对刺激反应的适应性，其反馈作用主要通过高级视区兴奋性谷氨酸能神经元介导。（3）抑制高级视皮层7区的反馈作用后，行为学和V1神经元的CSF曲线在相同的SF水平出现显著降低；在反馈作用抑制前后，行为学CSF曲线与V1神经元的CSF曲线有高度的相关性。（4）抑制7区的反馈作用后，行为学和V1神经元的TvC曲线在各噪声水平的TC出现显著升高；在反馈作用抑制前后，行为学TvC曲线与V1神经元的TvC曲线有高度的相关性。（5）行为学TvC和V1神经元TvC曲线的知觉模板模型（Perceptual Template Model）分析表明，7区反馈作用可能通过降低知觉模板的内部噪声（internal additive noise）和增加外噪声排除（external noise exclusion）机制提高行为学和V1神经元对信号检测的对比敏感度。本研究结果表明，高级脑区可通过反馈调控V1神经元对刺激反应的对比敏感度来影响行为学视觉对比度检测，这为进一步阐明视知觉形成的神经机制的研究提供了重要线索。