Gustotopic mapping in humans: a high resolution fmri study to assess detailed topography and modulations

个人如何以及为什么会对口味有不同的感知？我们的味觉进化是为了鼓励营养的消耗，并避免摄入危险物质。然而，今天，甜味和咸味的积极体验可能导致过度消费及其对健康的相关有害影响。相反，苦味和酸味也会阻止一些人食用更健康的食物，如苦味的绿色蔬菜。通过对味觉的深入研究，我们可以帮助营养政策制定者和食品行业开发健康的饮食和食品，从而改善整个社会的健康和福祉。味觉分为五类：甜、苦、鲜、咸和酸，这些味觉的感受器位于舌头乳头的味觉感受器细胞上。这项提案的重点是绘制大脑如何处理这些来自口腔的味觉信号。现代神经影像学方法使直接在人体中研究许多神经科学问题成为可能。例如，通过使用功能性磁共振成像（fMRI），我们可以跟踪伴随神经活动增加的局部血流变化。我们可以测量当受试者食用不同的促味剂时，大脑的哪些部分更活跃。研究我们味觉背后的神经机制的一个问题是，在人类大脑中，这些反应相对较小。使用尖端技术，我们可以在活体人脑中以非常高的空间分辨率测量人类皮层的神经反应。通过使用超高场磁共振成像技术，我们可以以比以前更高的空间分辨率非侵入性地测量强大的神经反应，同时评估感知的味觉，将感知和大脑的反应联系起来。在这个提议中，我们将研究是否可以识别初级味觉皮层中处理甜，苦，使用先进的大脑扫描技术来检测鲜味（一种美味的感觉）、咸和酸的味道。关于是否存在某些其他“味道”，特别是“脂肪”（脂肪酸）和金属“味道”，存在争议。我们计划确定这些刺激是否以及在哪里在初级味觉皮层中进行处理，为这些感觉是否应该被称为味觉提供证据。此外，我们将研究最近被称为热诱导味觉的现象，即当舌头快速加热或冷却时，一些人报告味觉感觉，尽管没有物理味觉刺激。由于对味觉的敏感度因人而异，我们将确定大脑处理如何受到这些已知的味觉差异的影响。我们也有兴趣看看温度引起的幻味是否以及如何改变大脑初级味觉皮层的反应。当他们的舌头快速冷却或加热时，将扫描热味觉者的大脑（先前在热刺激时报告甜味或苦味）。这将使我们能够确定幻象味觉是否调节与真实的味觉刺激相关的初级味觉皮层的同一区域。使用不同浓度的味觉刺激，我们还将探索浓度如何调节大脑反应。已知味道的组合会改变感知，例如甜味减少苦味，而鲜味增强咸味。在最后一个实验中，我们将问的问题，为什么混合促味剂可以导致增强或抑制味觉通过评估大脑的反应，成对的混合物的促味剂，并调查这些抑制和增强效果的皮质代表。总的来说，这项研究将大大促进我们对人类味觉的理解。

How and why do individuals perceive tastes differently? Our sense of taste evolved to encourage the consumption of nutrients, and to avoid ingestion of dangerous substances. However, today, the positive experience of sweet and salty taste can lead to the overconsumption and its associated detrimental effects on health. Conversely, bitterness and acidity can also prevent some individuals from consuming healthier foods such as bitter tasting green vegetables. Research progressing our fundamental understanding of taste perception will inform nutritional policy makers and the food industry to develop healthy diets and food products, hence improving the health and well-being of society in general.There are five categories of taste: sweet, bitter, umami, salty and acidic, and the receptors for these tastes have been identified on taste receptor cells housed in papillae on the tongue. This proposal focuses on mapping how the brain processes these taste signals from the mouth. Modern neuroimaging methods have made it possible to study many neuroscience questions directly in the human. By using functional magnetic resonance imaging (fMRI), for example, we can track changes in the local blood flow that accompanies increased neural activity. We can measure which parts of the brain are more active while subjects consume different tastants. One of the problems with studying the neural mechanisms underlying our sense of taste is that in the human brain, these responses are relatively small. Using cutting-edge technology we can measure neural responses in the human cortex at very high spatial resolution in the living human brain. By using ultra-high-field magnetic resonance imaging techniques, we can measure robust neural responses non-invasively at a much higher spatial resolution than has previously been possible, whilst concurrently assessing perceived taste sensations, linking perception and the brain's responses.In this proposal, we will investigate whether specific areas of the brain in the primary taste cortex can be identified that process sweet, bitter, umami (a savoury sensation), salty and sour tastes using improved state-of-the-art brain scanning technology. There is debate as to whether certain other 'tastes' exist, in particular 'fat' (fatty acid) and metallic 'taste'. We plan to determine if, and where, these stimuli are processed in the primary taste cortex, providing evidence as to whether these sensations should be termed tastes.In addition we will study a recent phenomenon known as thermally induced taste whereby some individuals report a taste sensation, although there is no physical taste stimulus present, when the tongue is rapidly heated or cooled. As sensitivity to taste varies across individuals, we will determine how brain processing is affected by these known differences in taste perception. We are also interested to see if, and how, the phantom taste induced by temperature changes the brain's response in the primary taste cortex. The brains of thermal tasters (previously reporting sweet or bitter taste upon thermal stimulation) will be scanned whilst their tongue is rapidly cooled or warmed. This will enable us to determine if the phantom taste sensation modulates the same area of the primary taste cortex as is related to real taste stimuli.Using different concentrations of taste stimuli we will also explore how concentration modulates brain response. Combinations of tastes are known to modify perception, for example sweetness reduces bitterness, and umami enhances saltiness. In a final experiment, we will ask the question of why mixing tastants can lead to enhancement or suppression of taste perception by assessing the brain's response to paired mixtures of tastants, and investigating the cortical representation of these suppression and enhancement effects. Overall, this research will considerably advance our understanding of human taste perception.