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Inclusion Criteria:

* Diagnosed with PD having a verbal fluency deficit based on neuropsychological test (T-score \< 40 or a T-score \<-1.0 SD below the average T-score): Semantic Object Retrieval Test (SORT), COWAT (both letter and category fluency), Boston Naming Test (BNT), Rey Auditory Verbal Learning Test (RAVLT)
* 50 - 90 years old
* Capable of understanding and signing an informed consent (able to answer consent comprehension questions)
* Fluent in speaking and reading English

Exclusion Criteria:

A potentially study-confounding, tDCS-contraindicated, or EEG-contraindicated psychological, neuropsychiatric, neurological, or other medical issues:

* Montreal Cognitve Assessment (MOCA) score \<23, unless an accompanying study partner/caregiver is with them and we can obtain the written consent of both the participant and the participant's accompanying study partner/caregiver (i.e., the participant's spouse, adult child, parent, or adult sibling);
* history of seizures;
* unexplained episodes of loss of consciousness (as these may be related to brain alterations or epilepsy);
* suffering from severe or frequent headaches;
* unstable or uncontrolled neuropsychiatric illness;
* severe traumatic brain injury (based on the Ohio State TBI Identification; Method);
* brain tumor; stroke; present drug abuse/misuse;
* brain tumor;
* serious or life-threatening diseases, including congestive heart failure, chronic obstructive pulmonary disease, or active malignancy;
* Huntington's disease;
* stroke;
* cranial implants or skull defects that affect tDCS administration;
* implanted brain medical devices, including, deep brain stimulators (DBS);
* implanted pacemakers;
* any electrically, magnetically, or mechanically activated implants;
* cardiac, neural, or medication implants;
* vascular clips or other electrically sensitive support systems in the brain;
* damaged skin at the sites of stimulation (the device should only be used on healthy, intact skin, as wounds may alter resistance to current);
* skin conditions such as dermatitis, psoriasis, or eczema;
* pregnant women;
* diagnosis of just dysarthria;

Use of medications that interact with or potentially interact with tDCS or EEG effects:

* anti-convulsants;
* carbamazepine;
* sulpiride;
* pergolide;
* lorazepam;
* rivastigmine;
* dextromethorphan;
* D-cycloserine;
* flunarizine;
* ropinirole;
* citalopram;
* stimulants;

Additionally, non-English speakers will be excluded because not all of the screening forms, questionnaires, and tests are available in languages other than English.

• Richardson, Texas, United States