Shared neural geometries for bilingual semantic representations

ABSTRACT The human brain has the remarkable ability to comprehend and express similar concepts in multiple languages. To understand how it does so, we examined responses of hippocampal neurons during passive listening, directed speaking, and spontaneous conversation, in both English and Spanish, in a small group of balanced bilinguals. We find a small number of putative cross-language neurons, whose responses to equivalent words (e.g., “tierra” and “earth”) are correlated. However, neurons’ semantic tunings differed substantially by language, suggesting language-specific neural implementations. Instead, the crucial driver of translation was a preserved geometric organization of neural responses between the two languages, one that did not depend on neuron level functional overlap. Indeed, that geometry was implemented by a common set of neurons along distinct readout axes; this difference in readout may help prevent cross-language interference. Together, these results suggest that hippocampus encodes a language-independent internal model for meaning. Competing Interest Statement S.A.S has consulting agreements with Boston Scientific, Zimmer Biomet, Koh Young, Abbott, and Neuropace. SAS is Co-founder of Motif Neurotech Footnotes Modest changes throughout the manuscript based on comments from colleagues, including a few improvements to the analyses and figures, a tweak to the title and abstract.