CIMEC - Center for Mind/Brain Sciences, University of Trento, Italy.
CIMEC - Center for Mind/Brain Sciences, University of Trento, Italy.
Neuroimage. 2021 May 15;232:117876. doi: 10.1016/j.neuroimage.2021.117876. Epub 2021 Feb 24.
Relational information about items in memory is thought to be represented in our brain thanks to an internal comprehensive model, also referred to as a "cognitive map". In the human neuroimaging literature, two signatures of bi-dimensional cognitive maps have been reported: the grid-like code and the distance-dependent code. While these kinds of representation were previously observed during spatial navigation and, more recently, during processing of perceptual stimuli, it is still an open question whether they also underlie the representation of the most basic items of language: words. Here we taught human participants the meaning of novel words as arbitrary labels for a set of audiovisual objects varying orthogonally in size and sound. The novel words were therefore conceivable as points in a navigable 2D map of meaning. While subjects performed a word comparison task, we recorded their brain activity using functional magnetic resonance imaging (fMRI). By applying a combination of representational similarity and fMRI-adaptation analyses, we found evidence of (i) a grid-like code, in the right postero-medial entorhinal cortex, representing the relative angular positions of words in the word space, and (ii) a distance-dependent code, in medial prefrontal, orbitofrontal, and mid-cingulate cortices, representing the Euclidean distance between words. Additionally, we found evidence that the brain also separately represents the single dimensions of word meaning: their implied size, encoded in visual areas, and their implied sound, in Heschl's gyrus/Insula. These results support the idea that the meaning of words, when they are organized along two dimensions, is represented in the human brain across multiple maps of different dimensionality. SIGNIFICANT STATEMENT: How do we represent the meaning of words and perform comparative judgements on them in our brain? According to influential theories, concepts are conceivable as points of an internal map (where distance represents similarity) that, as the physical space, can be mentally navigated. Here we use fMRI to show that when humans compare newly learnt words, they recruit a grid-like and a distance code, the same types of neural codes that, in mammals, represent relations between locations in the environment and support physical navigation between them.
记忆中物品的关系信息被认为是通过大脑内部的综合模型（也称为“认知地图”）来表示的。在人类神经影像学文献中，已经报道了二维认知地图的两个特征：网格状编码和距离依赖编码。虽然这些类型的表示以前在空间导航中观察到，并且最近在处理感知刺激时也观察到了，但它们是否也为语言中最基本的项目（即单词）的表示提供了基础，这仍然是一个悬而未决的问题。在这里，我们向人类参与者教授了新单词的含义，将其作为一组大小和声音正交变化的视听对象的任意标签。因此，新单词可以想象为在可导航的 2D 意义地图上的点。当受试者执行单词比较任务时，我们使用功能磁共振成像（fMRI）记录他们的大脑活动。通过应用表示相似性和 fMRI 适应分析的组合，我们发现了以下证据：（i）在右侧后内侧内嗅皮层中存在网格状编码，用于表示单词在单词空间中的相对角度位置，以及（ii）在 medial prefrontal、orbitofrontal 和 mid-cingulate cortices 中存在距离依赖编码，用于表示单词之间的欧几里得距离。此外，我们发现证据表明，大脑还分别表示单词含义的单一维度：其隐含的大小，在视觉区域中编码，以及其隐含的声音，在 Heschl's gyrus/Insula 中编码。这些结果支持了这样一种观点，即当单词按照两个维度组织时，它们在人类大脑中的表示跨越了多个不同维度的地图。重要声明：我们如何在大脑中表示单词的含义并对它们进行比较判断？根据有影响力的理论，概念可以想象为内部地图上的点（其中距离代表相似性），就像物理空间一样，可以在心理上进行导航。在这里，我们使用 fMRI 表明，当人类比较新学习的单词时，他们会招募网格状和距离编码，这些类型的神经编码与哺乳动物中表示环境中位置之间关系并支持它们之间的物理导航的编码相同。
