Cerebellum and Grammar Processing

Cortical and subcortical circuits of the brain contain regions of interest involved in grammar processing. Advances in neuroimaging techniques and neuroscience, reflected in a growing literature on the subject, are extending our understanding of how and where the brain processes the many intricacies of grammar in human language. Historically, linguistic functions were conceived as highly localized in specialized brain regions of the dominant cerebral cortex. Thus, the Broca area was responsible for expressive and the Wernicke area for receptive linguistic functions. This view has been revised in favor of more distributed language processing networks involving cortical and subcortical brain structures. Thus the Broca (the left inferior frontal cortex) and Wernicke areas (the left superior temporal cortex) are connected with contralateral cortex, ipsilateral insula, and subcortical brain structures of both hemispheres, such that the left inferior frontal and left superior temporal cortices are substantially involved in large-scale language processing in both comprehension and production of sentences (Friederici, Ruschemeyer, Hahne, & Fiebach, 2003; Shapiro & Caramazza, 2004). Thus, in this contemporary model, grammar processing is not restricted to cerebral cortex, but also engages several subcortical areas, forming part of a large-scaled matrix handling grammatical operations. Whereas motor control functions of these subcortical areas—for example, in the articulation of speech—are well-established in the neuroscience research literature, nonmotor functions, particularly in language domains, have been increasingly studied in linguistic and neuroscience research over the past two decades. As a result, the cerebellum and basal ganglia are now acknowledged to be involved in the cerebral networks that handle distinct grammatical aspects (Booth, Wood, Lu, Houk, & Bitan, 2 007; Friederici, 2004; Kotz, Schwartze, & Schmidt-Kassow, 2009). Clinical, neurophysiological, and neuroimaging studies have confirmed cerebellar contributions to grammar processing in both expressive and receptive domains (Ackermann, Graber, Hertrich, & Daum, 1999; De Smet, Baillieux, De Deyn, Marien, & Paquier, 2007; Fabbro, Moretti, & Bava, 2000; Gasparini et al ., 1999; Justus, 2004; Silveri, Leggio, & Molinari, 1994). In the 1990s, a possible role of the cerebellum in morphological, syntactic, and lexical aspects of grammar was put forward, gathering a variety of cerebellar contributions to grammar. These early studies indicated involvement of the cerebellum in detection of deviations from predicted grammar rules such as subject-verb agreement or canonical word order (Leiner, Leiner, & Dow, 1991, 1993; Silveri et al ., 1994). Subsequent investigations substantiated and extended this view of cerebellar contributions to include motorindependent comprehensive grammar analysis of sentence structure (Adamaszek et al ., 2012; Justus, 2004; Kotz et al ., 2009; Marien et al ., 2001; Witt, Nuhsman, & Deuschl, 2002). Thus, the cerebellum has been described as subserving the detection and marking of time intervals necessary for different sensorimotor and cognitive activities (Ivry & Richardson, 2002; Salman, 2002), the estimation of phonetic and semantic borders of syntagmata, and the maintenance of phrase structure in working memory during processing (Marien et al ., 2001). Precise details of such localized contributions and how they may contribute to large-scale networks integrating activity across multiple brain regions are still being worked out. Current controversies are discussed in this chapter along with a critical overview of the relevant literature.