Words On The Brain: A Semantic Map of the Cortex

In a new Nature paper, Berkely neuroscientists Alexander G. Huth and colleagues present a 'semantic atlas' of the human brain. Huth et al. have mapped which brain areas respond to words, according to the semantics (meanings) of each word. It turns out that these maps are highly similar across individuals - which could have implications for 'mind reading' technology. Huth et al. recorded brain activity with fMRI while seven volunteers listened to over two hours of audio narrative (taken from the award winning 'Moth Radio Hour' series.) The purpose of this was to determine the pattern of neural responses associated with different words. In total, there were over 10,470 English words in the Moth narratives. To make it feasible to analyse these, Huth et al. first calculated the co-occurrence between each word and 985 common English words, which served as semantic 'markers'. For instance, a word which has a high co-occurrence with "worry" is likely to mean something related to anxiety. Finally, Huth et al. used principle component analysis (PCA) on the co-occurrence data to find a small number of factors or components. These components are high-level semantic domains. For instance, component 1 (PC1) indexes the 'humanness' of words, with high scores on PC1 for words related to categories related to humans and human society and emotions. PC2 seemed to capture the "sensoryness" of words, with concrete, sensory terms scoring high on PC2 while abstract, intangible words scored low. So where in the brain are these semantic categories encoded? The image below shows the data from one of the participants, S2. Neural activity in response to PC1 is shown in red, PC2 is green and PC3 is blue.