Transcranial Cerebellar Direct Current Stimulation Enhances Verb Generation but Not Verb Naming in Poststroke Aphasia

Although the role of the cerebellum in motor function is well recognized, its involvement in the lexical domain remains to be further elucidated. Indeed, it has not yet been clarified whether the cerebellum is a language structure per se or whether it contributes to language processing when other cognitive com- ponents (e.g., cognitive effort, working memory) are required by the language task. Neuromodulation studies on healthy partici- pants have suggested that cerebellar transcranial direct current stimulation (tDCS) is a valuable tool to modulate cognitive func- tions. However, so far, only a single case study has investigated whether cerebellar stimulation enhances language recovery in aphasic individuals. In a randomized, crossover, double-blind de- sign, we explored the effect of cerebellar tDCS coupled with lan- INTRODUCTION During the past two decades, converging neuroscientific evidence has largely documented that the human cere- bellum contributes to a much wider range of higher-level cerebral functions than previously accepted. Indeed, although, traditionally, there has been a unanimous agreement that the cerebellum is primarily involved in autonomic and somatic motor processes (Leiner, 2010; Schmahmann, 2010; Strick, Dum, & Fiez, 2009; De Smet, Baillieux, De Deyn, Mariën, & Paquier, 2007; Holmes, 1939), particularly after aphasia reports, there has been a rapidly increasing interest in the cerebellum’s role in cognition (Reeber, Otis, & Sillitoe, 2013; Manto & Haines, 2012; Strick et al., 2009). Indeed, several linguistic dis- orders after acquired cerebellar lesions have been docu- mented (De Smet et al., 2007), such as impaired verbal fluency (Meinzer, Yetim, McMahon, & de Zubicaray, 2016; Stoodley & Schmahmann, 2009; Richter et al., 2007; Leggio, Silveri, Petrosini, & Molinari, 2000; Schmahmann & Sherman, 1998; Molinari, Leggio, & Silveri, 1997; Appollonio, Grafman, Schwartz, Massaquoi, & Hallett, 1993; Akshoomoff, 1Università Federico II, Naples, Italy, 2IRCCS Fondazione Santa Lucia, Rome, Italy, 3Università degli Studi di Roma Tor Vergata, Rome, Italy, 4Università degli Studi di Milano, Milan, Italy © 2017 Massachusetts Institute of Technology guage treatment for verb improvement in 12 aphasic individuals. Each participant received cerebellar tDCS (20 min, 2 mA) in four experimental conditions: (1) right cathodal and (2) sham stimu- lation during a verb generation task and (3) right cathodal and (4) sham stimulation during a verb naming task. Each ex- perimental condition was run in five consecutive daily sessions over 4 weeks. At the end of treatment, a significant improve- ment was found after cathodal stimulation only in the verb gen- eration task. No significant differences were present for verb naming among the two conditions. We hypothesize that cere- bellar tDCS is a viable tool for recovery from aphasia but only when the language task, such as verb generation, also demands the activation of nonlinguistic strategies.