A role for the dominant thalamus in language? A linguistic comparison of two cases subsequent to unilateral thalamotomy procedures in the dominant and non-dominant hemispheres

Abstract

Background : Thalamotomy has been reported to be successful in ameliorating the motor symptoms of tremor and/or rigidity in people with Parkinson's disease (PD), emphasising the bona fide contribution of this subcortical nucleus to the neural circuitry subserving motor function. Despite evidence of parallel yet segregated associative and motor corticosubcortical-cortical circuits, comparatively few studies have investigated the effects of this procedure on cognitive functions. In particular, research pertaining to the impact of thalamotomy on linguistic processes is fundamentally lacking. Aims : The purpose of this research was to investigate the effects of thalamotomy in the language dominant and non-dominant hemispheres on linguistic functioning, relative to operative theoretical models of subcortical participation in language. This paper compares the linguistic profiles of two males with PD, aged 75 years (10 years of formal education) and 62 years (22 years of formal education), subsequent to unilateral thalamotomy procedures within the language dominant and non-dominant hemispheres, respectively. Methods & Procedures : Comprehensive linguistic profiles comprising general and high-level linguistic abilities in addition to on-line semantic processing skills were compiled up to 1 month prior to surgery and 3 months post-operatively, within perceived "on periods (i.e., when optimally medicated). Pre- and post-operative language performances were compared within-subjects to a group of 16 non-surgical Parkinson's controls (NSPD) and a group of 16 non-neurologically impaired adults (NC). Outcomes & Results : The findings of this research suggest a laterality effect with regard to the contribution of the thalamus to high-level linguistic abilities and, potentially, the temporal processing of semantic information. This outcome supports the application of highlevel linguistic assessments and measures of semantic processing proficiency to the clinical management of individuals with dominant thalamic lesions. Conclusions : The results reported lend support to contemporary theories of dominant thalamic participation in language, serving to further elucidate our current understanding of the role of subcortical structures in mediating linguistic processes, relevant to cortical hemispheric dominance.