Why Language Processing Recruits Modality Specific Brain Regions: It Is Not About Understanding Words, but About Modelling Situations.

Whether language comprehension requires the participation of brain structures that evolved for perception and action has been a subject of intense debate. While brain-imaging evidence for the involvement of such modality-specific regions has grown, the fact that lesions to these structures do not necessarily erase word knowledge has invited the conclusion that language-induced activity in these structures might not be essential for word recognition. Why language processing recruits these structures remains unanswered, however. Here, we examine the original findings from a slightly different perspective. We first consider the 'original' function of structures in modality-specific brain regions that are recruited by language activity. We propose that these structures help elaborate 'internal forward models' in motor control (c.f. emulators). Emulators are brain systems that capture the relationship between an action and its sensory consequences. During language processing emulators could thus allow accessing associative memories. We further postulate the existence of a linguistic system that exploits, in a rule-based manner, emulators and other nonlinguistic brain systems, to gain complementary (and redundant) information during language processing. Emulators are therefore just one of several sources of information. We emphasize that whether a given word-form triggers activity in modality-specific brain regions depends on the linguistic context and not on the word-form as such. The role of modality-specific systems in language processing is thus not to help understanding words but to model the verbally depicted situation by supplying memorized context information. We present a model derived from these assumptions and provide predictions and perspectives for future research.