Hippocampal contributions to language: evidence of referential processing deficits in amnesia

A growing body of work suggests the hippocampus contributes to a variety of cognitive domains beyond its traditional role in memory. We propose that the hippocampus, in its capacity for relational binding, representational flexibility, and online maintenance and integration of multimodal relational representations, is a key contributor to language processing. Here we test the hypothesis that the online interpretation of pronouns is hippocampus-dependent. We combined eye tracking with neuropsychological methods, where participants (4 patients with bilateral hippocampal damage and severe declarative memory impairment, 4 patients with ventromedial prefrontal cortex [vmPFC] damage, and healthy comparison participants) viewed a scene while listening to short dialogues introducing 2 characters; for example, Melissa is playing violin for Debbie/Danny as the sun is shining overhead. She is wearing a blue/purple dress. Consistent with previous work, analysis of eye gaze showed that younger and older healthy comparison participants and the vmPFC patients rapidly identified the intended referent of the pronoun when gender uniquely identified the referent, and when it did not, they showed a preference to interpret the pronoun as referring to the first-mentioned character. By contrast, hippocampal patients, while exhibiting a similar gender effect, exhibited significant disruptions in their ability to use information about which character had been mentioned first to interpret the pronoun. This finding suggests that the hippocampus plays a role in maintaining and integrating information even over a very short discourse history. These observed disruptions in referential processing demonstrate how promiscuously the hallmark processing features of the hippocampus are used in service of a variety of cognitive domains including language.