Investigating scene processing in the human brain

每天，我们都在理解复杂的视觉环境，以执行简单但必要的行为。这些行为统称为导航功能，包括识别周围环境（例如在厨房内），选择合适的导航路径（例如通过休息室进入走廊的路线），识别与之互动的物体（例如灯开关）以及避开障碍物（例如咖啡桌）。尽管我们进行这些行为很重要，也很容易，但我们对大脑，尤其是视觉皮层是如何组织起来完成这些行为的知之甚少。这种知识差距的一个潜在原因是，关于视觉皮层组织的观点在历史上是由两种不同的观点形成的，而这两种观点在很大程度上是独立的。第一种观点关注的是视野中位置的重要性，它基于这样一个事实，即视觉皮层的早期阶段包含视野的空间地图，称为视野地图。与此相反，第二种观点认为，大脑中包含一些特殊的区域，可以选择特定的类别，比如面孔和场景。这些类别选择区域位于视觉皮层的后期阶段，被认为对视野中的位置不敏感，并且独立于这些早期的视野地图。然而，最近的证据已经确定了整个大脑的视野地图，远远超出了视觉皮层的早期阶段。此外，一些类别选择区域在空间上重叠了多个地图。这种空间重叠表明了这两个原则之间的相互作用，并提出了一个基本的、尚未回答的问题：这些视野地图在视觉感知中扮演什么角色？我们的目标是回答这个问题，这个问题与大脑的一个场景选择区域有关，被称为枕地区（OPA）和它重叠的视野地图。OPA对场景图像的反应比对其他类别的反应更强烈，可能在我们有效导航的能力中发挥作用。有趣的是，我们团队最近的研究发现，至少有五个独立的视野地图重叠在OPA上。这一发现令人惊讶，因为长期以来人们一直认为，类别选择区域对视野位置不敏感。它还提出了这样一种可能性，即这些地图中的每一个都执行不同但互补的功能。我们的目标是通过利用不同技术的优势来测试这种可能性。首先，我们将使用功能性磁共振成像（fMRI）来识别OPA及其在个体参与者中重叠的视野图。一旦确定，我们将使用功能磁共振成像测量在处理不同类型场景时这些地图上的活动。FMRI允许人们测量非常小（约2mm）的大脑区域的活动，尽管相对缓慢（例如每2秒）。我们将通过使用一种每毫秒测量大脑活动的技术-脑磁图（MEG）来克服功能磁共振成像的相对滞后。这将提供场景处理何时发生的措施，例如在决定通过房间的路线时。最后，我们将使用一种称为经颅磁刺激（TMS）的技术来测试这些大脑区域处理的因果性质。在颅磁刺激过程中，一个快速变化的磁场被传送到头部的一小部分。这种磁场会暂时无痛地扰乱受刺激大脑区域的正常活动。与功能磁共振成像和脑磁图间接测量大脑活动不同，经颅磁刺激可以提供单个区域对特定任务的贡献的因果证据。通过一系列新颖而雄心勃勃的项目，我们的目标是建立OPA视野地图在复杂的视觉过程中发挥的作用，例如那些涉及导航功能的视觉过程。

Every day, we make sense of complex visual environments to carry out simple, yet essential behaviours. These behaviours, which together are referred to as navigational affordances, include identifying our surroundings (e.g. inside a kitchen), selecting appropriate paths for navigation (e.g. the route through your lounge and into your hallway), recognising objects to interact with (e.g. light switches) and avoiding obstacles (e.g. the coffee table). Despite the importance and ease at which we perform these behaviours, we know relatively little about how the brain, and the visual cortex in particular is organised to accomplish this. One potential reason for this knowledge gap is that ideas about the organisation of visual cortex have been shaped historically by two different perspectives that were largely independent.The first perspective focused on the importance of positions in the visual field and was grounded in the fact that early stages of visual cortex contains spatial maps of the visual field called visual field maps. In contrast, the second perspective proposed that the brain contains special areas selective to certain categories, such as faces and scenes. These category-selective areas, located at later stages of visual cortex, were thought to be insensitive to positions in the visual field and independent from these early visual field maps. However, recent evidence has identified visual field maps throughout the brain, spreading far beyond the early stages of visual cortex. Moreover, several category-selective areas have been shown to spatially overlap multiple maps. This spatial overlap suggests an interaction between these two principles and raises a fundamental and as yet unanswered question: What role do these visual field maps play in visual perception?It is this question that we aim to answer with respect to a scene-selective area of the brain, referred to as the Occipital Place Area (OPA) and the visual field maps it overlaps. OPA responds more strongly to images of scenes than to other categories and may play a role in our ability to navigate effectively. Intriguingly, recent research by our team identified at least five separate visual field maps overlapping OPA. This finding is surprising given the long-held idea that category-selective areas are insensitive to visual field position. It also raises the possibility that each of these maps performs different, yet complementary functions. We aim to test this possibility by capitalising on the strengths of different techniques. First, we will use functional magnetic resonance imaging (fMRI) to identify both OPA and the visual field map it overlaps in individual participants. Once identified, we will measure the activity in these maps during the processing of different types of scenes using fMRI. FMRI allows one to measure the activity of very small (~2mm) areas of the brain albeit relatively slowly (e.g. every 2 s). We will overcome the relative sluggishness of fMRI by using a technique that measures brain activity every millisecond - magnetoencephalography (MEG). This will provide measures of when in time aspects of scene processing occur, such as when deciding on the route to take through a room. Finally, we will test the causal nature of processing in these brain areas using a technique called transcranial magnetic stimulation (TMS). During TMS, a rapidly changing magnetic field is delivered to a small part of the head. This magnetic field temporarily and painlessly disrupts the normal activity of the stimulated brain region. Unlike both fMRI and MEG, which provide indirect measurements of brain activity, TMS can provide causal evidence of the contribution of individual areas to a particular task. Through a series of novel and ambitious projects we aim to establish the role that OPA visual field maps play in complex visual processes such as those involved in navigational affordances.