Striatal degeneration impairs language learning: evidence from Huntington's disease

Abstract

Although the role of the striatum in language processing is still largely unclear, a number of recent proposals have outlined its specific contribution. Different studies report evidence converging to a picture where the striatum may be involved in those aspects of rule-application requiring non-automatized behaviour. This is the main characteristic of the earliest phases of language acquisition that require the online detection of distant dependencies and the creation of syntactic categories by means of rule learning. Learning of sequences and categorization processes in non-language domains has been known to require striatal recruitment. Thus, we hypothesized that the striatum should play a prominent role in the extraction of rules in learning a language. We studied 13 pre-symptomatic gene-carriers and 22 early stage patients of Huntington's disease (pre-HD), both characterized by a progressive degeneration of the striatum and 21 late stage patients Huntington's disease (18 stage II, two stage III and one stage IV) where cortical degeneration accompanies striatal degeneration. When presented with a simplified artificial language where words and rules could be extracted, early stage Huntington's disease patients (stage I) were impaired in the learning test, demonstrating a greater impairment in rule than word learning compared to the 20 age- and education-matched controls. Huntington's disease patients at later stages were impaired both on word and rule learning. While spared in their overall performance, gene-carriers having learned a set of abstract artificial language rules were then impaired in the transfer of those rules to similar artificial language structures. The correlation analyses among several neuropsychological tests assessing executive function showed that rule learning correlated with tests requiring working memory and attentional control, while word learning correlated with a test involving episodic memory. These learning impairments significantly correlated with the bicaudate ratio. The overall results support striatal involvement in rule extraction from speech and suggest that language acquisition requires several aspects of memory and executive functions for word and rule learning.

Procedural Learning and Individual Differences in Language

“…Much classic evidence of the basal ganglia mediation in language comes from studies of patients with striatal damage. For example, individuals with Huntington's disease showed difficulty learning a simplified artificial language, wherein novel words followed artificial grammatical rules and no semantic representations were accessible (De Diego-Balaguer et al, 2008). In addition, they demonstrated inefficient use of purely syntactic operations during sentence comprehension (Teichmann et al, 2005).…”

Language deficits in pre-symptomatic Huntington’s disease: Evidence from Hungarian

“…Because the present study focuses on Hungarian, an agglutinative language with complex morphology that has not been examined before in either HD or pre-HD, the results should be useful for testing the cross-linguistic validity of previous research on HD that has investigated similar aspects of language in both English (Longworth, Keenan, Barker, Marslen-Wilson, & Tyler, 2005; Ullman, et al, 1997) and French (Teichmann, Dupoux, Kouider, & Bachoud-Levi, 2006; Teichmann, et al, 2005). Finally, although previous studies of pre-HD have examined language-related tasks such as verbal fluency (Larsson, Almkvist, Luszcz, & Wahlin, 2008; Lawrence, et al, 1998) or artificial grammar (De Diego-Balaguer, et al, 2008), to our knowledge this is the first study that specifically examines morphology, or indeed any other particular component of the language system, in pre-HD.…”

Bilingualism at the core of the brain. Structural differences between bilinguals and monolinguals revealed by subcortical shape analysis

“…The basal ganglia have received increased attention regarding their functional role in a wide array of languagerelated processes, such as speech production (Binder et al 2005;Bohland and Guenther 2006;Kuljic-Obradovic 2003;Riecker et al 2002;Rosen et al 2000;Sakurai et al 1993), rule learning (De Diego-Balaguer et al 2008), and phonological processing (Tettamanti et al 2005;Tricomi et al 2006;Watkins et al 2002), among others. The basal ganglia are an important component of the procedural memory system, which underlies the extraction and computation of language regularities and rules (e.g., mental grammar) (Ullman, 2004).…”