The contribution of the hippocampus to language processing

Resumo

Humans display distinct unlimited capacity to produce expressions in lan- guage and use them flexibly in language processing.This characteristic of human language allows speakers to use novel, flexible, and complex struc- tures during communication. Neurobiologically, however, it is not fully un- derstood how the rapid process of language production and language com- prehension occurs, including word generation, interpretations and common representations that facilitate the process of real-time language processing. The classical theories and approaches have limited the language network to perisylvian cortical regions, namely the Broca’s and Wernicke’s areas. This thesis proposes that the language network goes beyond the cortical regions indicated by traditional views. In doing so, this thesis puts forward a hy- pothesis that subcortical structures are not only fundamental to memory but also to language, in which online language processing receives a ma- jor contribution from the hippocampal declarative memory, which allows speakers and listeners to use language flexibly. The mechanism of such a contribution by the hippocampal declarative memory system during online language processing is via relational binding in which hippocampal declar- ative memory rapidly retrieves a network of relative, stored information to serve in the particular context. To support the hypothesis of hippocampal implications in language pro- cessing, several pathologies that affect the hippocampus have been reviewed, including Alzheimer’s disease, Down syndrome, Williams’ syndrome, schizophre- nia, depression and bipolar disorder. The review evaluated hippocampal neurobiological alterations in each pathology, and determined cognitive and language profiles. Findings from previous pathologies indicate that the hip- pocampus affects language at two levels. First, in the general delay in lan- guage acquisition and other cognitive aspects, and second, in the disturbed use of language during online communication; short lag interaction is seen to occur when the hippocampal formation is lesioned. It appears that hip- pocampal lesions suppress the flexible use of stored information within cer- tain contexts in communication, as it does in flexible navigation in animal models. This thesis concludes that the hippocampus is a multi-cognitive operator that is implicated in several cognitive areas including the flexible use of language during real-time processing, and therefore it should be taken into account in the language network in the human brain.