Effects of tDCS on Apraxia of Speech in Non-Fluent Primary Progressive Aphasia

Overview

Primary progressive aphasia (PPA) is a neurodegenerative disease that affects first and foremost language abilities. There are three different variants of PPA, each a relatively distinct speech and language profile. For individuals with non-fluent variant PPA (nfvPPA), a core symptom is apraxia of speech (AOS), which is defined as an oral motor speech disorder. Such a disorder inhibits one's ability to translate speech plans into motor plans and results in longer segmental durations and reduced rate of syllabic production. This research project investigates the behavioral and neuromodulatory effects of transcranial direct current stimulation (tDCS) during language therapy in participants with nfvPPA over time. Anodal tDCS targeting the left inferior frontal gyrus (IFG) administered in combination with language therapy is expected to be more beneficial when compared to language therapy alone (sham). The investigators believe tDCS during language therapy will 1) improve language performance or decrease rate of decline, 2) promote better-sustained effects at 2 weeks and 2 months post-treatment, and 3) produce generalization to untrained language items and some other cognitive functions. Resting-state fMRI, diffusion tensor imaging (DTI), and volumetric data are also collected to investigate changes in functional brain connectivity associated with tDCS in individuals with PPA. A better understanding of the therapeutic and neuromodulatory mechanisms of tDCS as an adjunct to language therapy in nfvPPA may have a significant impact on the development of effective therapies for PPA, and may offer insight into ways of impeding neurodegeneration that may improve patients' quality of life, as well as extend patients' ability to work and manage patients' affairs.

A. Evaluation Tasks Language Tasks: Participants will be administered baseline language and cognitive tasks, including 1 or more of the following, depending on participants' residual language and cognitive skills: a) writing to dictation b) oral spelling c) oral and written naming of pictures d) word-picture matching f) written and oral picture description g) digit span h) spatial span i) verbal learning j) grammatical sentence production k) oral word repetition l) sentence comprehension Quality of Life questionnaires: Participants will be administered standardized and non-standardized quality-of-life questionnaires before, after, and at follow-up intervals of each experimental period. The purpose of these questionnaires is to assess whether the proposed interventions have affected participants' well-being and the general quality of participants' life. B. AOS Intervention Intervention involves oral word repetition of increasingly complex words. The goal is to improve volitional control of participants' articulators in order to produce co-articulated, intelligible speech, as well as improve prosody, voice quality, and speech fluency. C. Assessment of Language Therapy Tasks: Follow-up assessments will probe all sets of increasingly complex words targeted in intervention and as well as word sets not targeted in intervention to assess near-transfer generalization. Other language and cognitive tasks will be assessed for far-transfer generalization. Differences in baseline measures in pre- and post-intervention accuracy for word production for each patient will be evaluated using the following: percentages of total number of words correct, arithmetic differences between percentage scores, and permutation tests (Pearson's chi-square test; Fisher's exact test). C. tDCS Methods: Participants will take part in 10-15 consecutive training sessions (3-5 per week), separated by 2 months. Anodal tDCS has typically been shown to up-regulate neuronal excitability and produce enhancement of behavioral performance. A Soterix-CT device will be delivering current at an intensity of 1-2 mA (estimated current density 0.04 mA/cm\^2; estimated total charge 0.048 C/cm\^2) for a maximum of 20 minutes in the tDCS groups and for a maximum of 30 seconds in the Sham group. For both interventions (tDCS and Sham) the electrical current will be increased in a ramp-like fashion at the onset of the stimulation eliciting a transient tingling sensation on the scalp that usually disappears over seconds. D. Imaging Methods: Imaging will be performed at the beginning of enrollment, before and after each 12-to-15-day tDCS treatment, and at follow-up intervals for up to 8 time points per individual on a 3T Philips system, and will consist of resting-state fMRI (rsfMRI), MPRAGE, and diffusion tensor imaging (DTI). Each scanning session will last approximately 1 hour. E. Statistical Analyses: In the within-subject crossover protocol, each participant will be administered two experimental conditions: IFG tDCS+language (tDCS intervention) and IFG sham+language (sham treatment). All analyses, behavioral and imaging, will be under the oversight of the study statisticians. F. Study duration and number of study visits required of research participants. Before any intervention, participants will be randomly assigned to either sham or tDCS experimental conditions. After 1-3 weeks of tDCS application (3-5 sessions in a week, 10-15 sessions per stimulation site) there will be an interval of approximately 2 months and then the investigators will implement the other two tDCS conditions in a within-subject cross-over design. Participants will be followed-up at 2-week and 2-month follow-up intervals. G. Blinding, including justification for blinding or not blinding the trial, if applicable. Participants will be blinded to the application of anodal or sham tDCS. To achieve blinding, all participants will be fitted with the tDCS electrodes placed over the left inferior frontal gyrus (IFG). The Soterix-CT device will be used for double-blinding purposes. H. Justification of why participants will not receive routine care or will have current therapy stopped Participation in this study will not disrupt any current care or therapy. I. Justification for inclusion of a placebo or non-treatment group All participants will undergo active and sham conditions, thus serving as participants' own control. J. Definition of treatment failure or participant removal criteria Participants will be removed from the study if participants are unable to comply with task instructions or tolerate the tDCS procedure. K. Description of what happens to participants receiving therapy when study ends or if a participant's participation in the study ends prematurely When the study ends participants will continue to receive management with participants' neurologist as usual. If a patient's participation in the study ends prematurely s/he will still receive care as before. In sum, termination of the study or termination of participation in it will not affect regular therapy he or she may be receiving. L. Qualification of investigators: The principal investigator (PI) and co-investigators have extensive research and clinical experience with all study tasks: behavioral language therapy (including AOS intervention). The investigators have already published tDCS studies showing positive results in spelling.