认知与发展心理学研究室知识库

尽管神经系统发育存在“关键期”，但是在关键期以后，个体的大脑皮层仍然具有很强的可塑性。现在越来越多的研究表明大脑皮层的可塑性可能发生在视觉加工通路的各个阶段。皮层可塑性的发生不仅需要视觉刺激进行自下而上的驱动，更需要自上而下的调控，以实现视知觉能力的提升或改善。

识别客体运动和判断主体运动状态是绝大多数生物体的必备技能，包括人类在内的灵长类生物对运动信息的处理主要依赖视觉系统背侧通路的一系列脑区来完成。其中基于光流模式的自身运动方向判断主要由属于高级视觉皮层的MST和VIP脑区参与，而对光栅、散点平动方向的识别则在初、中级视觉皮层即可实现。

本研究采用清醒猴神经电生理胞外记录技术，考察了称猴VIP脑区神经元在自身运动方向判断任务训练中反应特性的变化，以及这种变化与动物行为变化的相关性。旨在探明:(1)自身运动方向判别训练对称猴行为和VIP神经元反应特性分别有什么影响?(2)称猴对自身运动方向判别能力的提升可否归因于VIP神经元信息加工能力的提高?

由于VIP脑区可能特点是参与自身运动方向判断中眼动补偿的神经计算，实验采用模拟自身朝不同方向运动的光流作为视觉刺激，并设定了无眼动、真实眼动和模拟眼动三种条件，目的是考察知觉训练引起的行为和神经元眼动补偿能力改变。其中模拟眼动是在称猴盯住注视点不动时，将真实眼动造成的视网膜图像扭曲直接呈献在显示器上，以保正无眼动信号参与时视觉信息输入与真实眼动条件下一致。

在行为层面上，我们发现称猴对光流刺激的分辨阂值不断降低，分辨能力不断提升，并且分辨能力存在对眼动条件的依赖性。从眼动补偿能力角度出发，个体在真实眼动条件下眼动补偿能力的提升不能迁移到模拟眼动条件，也就是说在有、无眼动信号参与时称猴应该采用了不同的方向判别策略以解决视网膜图像的扭曲，以识别真实的自身运动方向。

在神经机制层面，知觉训练能显著提高VIP神经元对最优方向和非最优方向间反应频率的幅值差异，进而提升VIP神经元对自身运动方向的分辨能力，但这种提升是普遍的，与眼动条件无关。此外，知觉训练对VIP神经元解决眼动补偿的能力没有显著的提升作用。

综合分析知觉训练对称猴行为和VIP神经元反应特性的影响，我们发现尽管VIP脑区活动与动物行为选择的相关性随训练而持续提高，但这种提高可能主要源于VIP神经元对光流敏感性的提升，而不是它们解决眼动补偿的能力。结合称猴在真实和模拟眼动条件下显然基于可用的视网膜与非视网膜信息采取了不同的策略以解决眼动补偿问题，我们可以推测VIP的功能角色主要还是对感知觉信息编码，而不过多参与如何利用这些信息形成准确判断甚至调整信息读取的策略。

训练是影响皮层变化的一种因素，自然老化也会造成皮层信息加工能力的改变。在客体运动知觉领域，研究者发现老化造成了老年人的在视运动知觉实验任务中存在空间抑制效应减弱的现象(Betts, et al, 2009; Betts, et al, 2005)。那么老化是否必然导致神经系统抑制效应的减弱呢?也许并非如此。我们分别采用运动互斥效应范式与空间抑制效应范式比较了年轻人与老年人在同样实验条件下的效应值，由于运动互斥效应被认为主要源于MT脑区对不同方向敏感神经元群体间的相互抑制，空间抑制效应源于中高级皮层脑区对初级皮层(V1)的反馈抑制，因此这项研究旨在探讨自然老化对视觉系统背侧通路中级皮层MT区和初级皮层V1区抑制功能的影响。我们发现尽管老年人比年轻人在空间抑制效应上表现出减弱趋势，在运动互斥效应上则表现为显著增强，意味着老化使对初级视皮层的反馈抑制减弱，但中级视皮层(MT)内侧抑制效应反倒是增强的。其神经机制可能是由于侧抑制源于对不同运动方向敏感的神经元群体间的相互抑制，而老化降低了神经元对运动方向编码的准确性，表现为调制曲线带宽增加且基线增高，进而使两个相互抑制的神经元群体调制曲线的重叠区域增加。因此，老化所引起的皮层功能变化并不一定必然导致神经系统抑制功能的减弱，要结合抑制类型来判断。

Although the development of neural system has a "critical period", there is still strong plasticity of the individual's cerebral cortex after the critical period. Recently, more and more studies showed that the plasticity of the cortex might occur at various stages of the visual pathway. The development of cortical plasticity not only requires to be driven by the bottom-up visual stimulation, but also requires top-down control, in order to promote and improve the ability of visual perception .

It is essential for most organisms to identify the motion of the object and to judge the heading direction, which is attributed to a series of areas in the dorsal pathway for the non-human primates and human beings. During the self-motion, the judgment of heading direction based on the optic flow pattern is accomplished by the MST area and VIP area, which belong to the higher level visual cortex. However, the direction of gabor and moving points could be recognized by the primary and secondary visual cortex.

In this study, we used the extracellular recording technique of the neural electrophysiology on the awake monkey, to examine the change of response characteristics for VIP neurons during the training of heading direction and the correlation between neuronal response and behavioral response. We would discuss

these following aspects: first, how does perceptual training affect the behavior of macaques and the response of VIP neurons? Second, could the plasticity of the neurons in VIP area sufficiently support the plasticity of the behavior? If not, what factors attribute to this enhancement?

As the possible function of the VIP area is involved in the neural computation of eye movement compensation during the heading perception. Our experiment used the optic flow to simulate people moving to different directions. We designed the fixation condition, the real pursuit condition, and the simulated pursuit condition in order to investigate the training effects of eye movement compensation on the behavioral level and the neuronal level. In the simulated pursuit condition, macaques focused a fixation point, the optic flow on the screen were the optic flow pattern on retina when the monkeys did the real pursuit. This manipulation ensured that the retina image during the simulated pursuit condition was the same as the real pursuit condition.

The results showed that, on the behavioral level,，there is a significant perceptual learning effect of the discrimination ability. The thresholds of rhesus monkeys for discriminating optic flow angle decreased. The sensitivity of behavior enhanced and the discrimination ability gradually increased. Moreover, the enhancement of discrimination ability was dependent on the condition of eye movement. For the eye movement compensation ability, the improvement of the eye movement compensation ability in the real pursuit condition cannot be transferred to the simulated pursuit condition. In other words, the macaques might adopt different direction discrimination strategies to solve the distortion of the retinal image problem, in order to identify the actual heading direction.

On the neural level, for the discrimination ability, perceptual training changed the information representation of heading perception in the VIP region. Perception training could make difference between maximum and minimum responses larger. The discrimination ability of VIP neurons could be significantly improved by the perceptual training. However, there is no significant interaction effects between the eye movement condition and the training stage which means that these improvements are common. For the eye movement compensation ability, perceptual training did not has significant effect on those neurons.

Comprehensive analysis of perception training effect on macaque behavior and response of VIP neurons, we found that although the correlation between the VIP neurons' response and the choice of macaque continuously improved, this enhancement might be derived from the improvement of discrimination ability of VIP neurons, rather than the ability of the eye movement compensation. Combination the result which the macaques might adopt different direction discrimination strategies to solve the distortion of the retinal image problem, we inferred that the functional role of VIP is mainly to encode perceptual information, rather than how to use this information to form accurate judgment and even to adjust reading-out rules.

Training is one of the factors that affect the change of cortex, and aging could also change the information processing ability of cortex. In the study of visual motion perception, researchers have found that aging has caused the weakening of the spatial inhibition effect of the elderly (Betts, et al, 2009; Betts, et al, 2005). However, is aging necessarily lead to a reduction in the inhibitory effect of the neural system? It is still unclear. In the second study, we used motion repulsion and surround suppression paradigm to compare the effect values of young and old people under the same experimental conditions. As the motion repulsion effects are thought to stem from mutual inhibition of MT areas neurons with different preferred directions, and the spatial inhibition effect is the result of the interaction between excitatory feedback connections and inhibitory horizontal connections, so our study aimed to explore the aging effect of inhibition mechanisms of MT area and V 1 area.

We found that motion repulsion effect was increased with aging and the surround suppression effect was reduced. These results suggested that aging caused the reduction of inhibitory effects of inter cortical feedback between the MT and the V 1 region. However, the cortical inhibition function of MT area was increased by aging. Because motion repulsion has been interpreted as arising from local mutual inhibition, which is that two groups of neurons with different preferred directions inhibit each other, our result suggest that aging may leads to enhanced local mutual inhibition. This might be due to the decrease of direction coding accuracy caused by aging, which is represented as the increase of the bandwidth and baseline of the neuron tuning curve, and then the overlapping regions of tuning curves increased. Therefore, the change of cortex function caused by aging does not necessarily lead to a reduction of the neural system inhibitory function, which should be judged by combining the suppression type.