The Functional Dissection of Motion Processing Pathways in the Human Visual Cortex: An fMRI-guided TMS Study

现代脑成像技术的发展，如功能磁共振成像(FMRI)，使神经科学家能够无与伦比地了解活着的人脑的内部工作原理。特别是视觉处理，已经被证明特别适合用功能磁共振成像进行研究。使用这项技术的研究揭示了大脑中不同网络的存在，这些网络由不同类型的视觉刺激激活，如运动、颜色、面孔、物体等。在这个研究项目中，我们感兴趣的是大脑如何分析有关运动刺激的信息。对视觉环境中运动的分析对于我们与外部世界的互动至关重要。它为我们提供了丰富的信息来源，帮助我们在周围环境中定位自己，帮助我们在这个环境中移动时避免和识别物体。大脑成像实验表明，当我们观察运动刺激时，这会在大脑内的大量视觉区域产生神经活动，这反映了运动感知的重要性。这些大脑区域中的许多区域都包含它们自己对外部世界或视野的单独表示。但似乎不太可能，也不是说效率低下，这些大脑区域中的每一个都执行完全相同的分析，并以完全相同的方式对我们的运动感知做出贡献。然而，这些不同的区域在我们对运动的感知中究竟扮演了什么角色，还远不清楚。虽然功能磁共振成像为我们提供了一种极好的方法，我们可以通过它来定位和绘制整个视觉大脑的不同区域，但它不太适合提供关于特定大脑区域内的神经活动是否对感知或行为至关重要的信息。然而，当功能磁共振成像与经颅磁刺激(TMS)相结合时，这些直接或因果联系就可以建立起来。TMS是一种非侵入性、无害的技术，可导致大脑小区域的神经功能一过性中断。如果这种神经活动对感知很重要，那么它的破坏可能会导致人类观察者执行特定视觉任务的能力受损，例如，决定刺激的方向运动。来自猴子大脑的实验证据表明，不同的运动区域对不同类型的运动刺激做出反应，如左右(平移)运动、光流(当我们在环境中移动时在视网膜上产生的一种径向运动)或由运动刺激定义的边界。这项工作提供了一个理论框架，可以在这个框架内研究人类大脑中运动处理的组织。使用我们的fMRI引导的TMS方法，我们的目标是在特定脑区的神经活动和感知不同类型运动刺激的能力之间建立直接关系。通过这样做，我们的目标是提供一个更完整的描述，说明这些大脑中对运动做出反应的每个区域是如何影响其知觉的。

The development of modern brain imaging techniques, such as functional magnetic resonance imaging (fMRI), has given neuroscientists unparalleled access to the inner workings of the living human brain. Visual processing in particular has proven to be particularly amenable to study with fMRI. Studies using this technique have revealed the existence of different networks in the brain that are activated by different kinds of visual stimuli, such as motion, colour, faces, objects and so forth. In this research project we are interested in how the brain analyses information about moving stimuli. The analysis of motion within our visual environment is vitally important to our interaction with the outside world. It provides us with a rich source of information that helps us orientate ourselves within our surroundings, aiding in the avoidance as well as in the recognition of objects as we move around in this environment. The importance of motion perception is reflected by the fact brain imaging experiments reveal that when we look at moving stimuli, this generates neural activity across a large number of visual areas within the brain. Many of these brain areas contain their own individual representation of the outside world or visual field. But it seems unlikely, not to say inefficient, that each of these brain areas performs exactly the same kind of analysis and contributes in exactly the same way to our perception of motion. Yet precisely what roles these different areas do play in our perception of motion, is far from clear. Whilst fMRI provides us with an excellent means by which we can localise and map different areas across the visual brain, it is less well suited to providing information as to whether neural activity within a particular brain area is crucial for perception or behaviour. However, these kinds of direct or causal links can be made when fMRI is combined with transcranial magnetic stimulation (TMS). TMS is a non-invasive and non-harmful technique which can bring about transient disruption of neural function in small areas of the brain. If this neural activity is important for perception, then its disruption can induce impairments in the ability of human observers to performance specific visual tasks, such a determining the direction motion of stimulus, for example. Experimental evidence from the monkey brain has shown that different motion areas are responsive to different kinds of moving stimuli such as left-right (translational) motion, optic flow (a kind of radial motion produced on the retina as we physically move through our environment) or boundaries defined by moving stimuli. This work has provided a theoretical framework within which the organisation of motion processing can be studied in the human brain. Using our fMRI-guided TMS approach we aim to establish direct relationships between neural activity within particular brain areas and the ability to perceive different kinds of moving stimuli. In so doing we aim to provide a more complete description as to how each of these brain areas that are responsive to motion contribute to its perception.