Table 2:
Summary of Reviewed tDCS Studies from 2015–2019.
| Author | Participants | Study Design | Stimulation Type | Stimulation location | Treatment sessions | Outcome Variable | Results |
|---|---|---|---|---|---|---|---|
| Branscheidt et al. 2018 | 16 chronic | Randomized, double blind, sham-controlled, cross over | Anodal tDCS | Left motor cortex | 1 session with tDCS and 1 with sham | Lexical Decision | Improved accuracy in lexical decision with anodal tDCS compared to sham. |
| Fridriksson et al. 2018 | 74 chronic | Randomized, double blind, sham-controlled Futility design |
Anodal tDCS | Left temporal lobe region with the highest naming related activation on the fMRI | 15 sessions with either tDCS or sham | Picture Naming | Improved picture naming for anodal tDCS compared to sham. |
| Pestalozzi et al. 2018 | 14 chronic | Randomized, double-blind, sham-controlled, crossover | Anodal tDCS | Left dorsolateral prefrontal cortex | 1 session with tDCS and 1 with sham | Picture Naming, Verbal Fluency, and Word Repetition | Improved verbal fluency and picture naming speed with anodal tDCS compared to sham. |
| Spielmann et al. 2018 | 58 subacute | Randomized, double-blind sham-controlled | Anodal tDCS | Left IFG | 5 sessions with tDCS or sham | Picture Naming | No significant improvement in naming with anodal tDCS compared to sham tDCS |
| Darkow et al. 2017 | 16 chronic | Randomized, sham-controlled, crossover trial | Anodal tDCS | Left primary motor cortex | 1 session with tDCS and 1 with sham | Picture naming, fMRI | No difference in naming accuracy between anodal tDCS and sham. Increased activity in language networks with anodal tDCS compared to sham. |
| Meinzer et al. 2016 | 26 chronic | Randomized, double-blind, sham-controlled | Anodal tDCS | Left primary motor cortex | 16 sessions (2 sessions per day) with either tDCS or sham | Picture naming and functional communication | Improvement for trained items noted for both anodal tDCS and sham. Generalization to untrained items and functional communication only for anodal tDCS condition |
| Campana et al. 2015 | 20 chronic | Randomized, double blind, sham-controlled, cross over | Anodal tDCS | Left IFG | 10 sessions with tDCS and 10 sessions with sham | Picture Description, Verb and Noun Naming | Significant improvement in picture description, verb and noun naming with anodal tDCS compared to sham. In addition, damage to distinct left hemispheric structures resulted in lower responses to anodal tDCS. |
| Wu et al., 2015 | 12 chronic | Sham-controlled, cross over study | Anodal tDCS | Left posterior perisylvian region | 20 sessions with tDCS and 40 with sham | Picture Naming and Auditory Word-Picture Identification, EEG | Improved picture naming and auditory comprehension with anodal tDCS. EEG analysis indicated that improved picture naming correlated with a higher activation level in wide areas of the left hemisphere and in isolated areas of the right hemisphere. |
| Santos et al. 2017 | 13 chronic | Randomized, double blind, sham-controlled, cross over | Anodal tDCS and inhibitory low frequency rTMS | tDCS: Left IFG rTMS: Right IFG | 1 session with tDCS, 1 session with rTMS and 1 with sham | Picture Naming | No significant difference between A-tDCS, rTMS and sham stimulation in picture naming |
| da Silva et al. 2018 | 14 chronic | Randomized, double-blind, sham-controlled | Cathodal tDCS | Right IFG | 5 sessions with either tDCS or sham No task (off-line tDCS) | Picture Naming | No significant results were observed for the Snodgrass test. Improved mean time for correct response with strategy for BNT with cathodal tDCS compared to sham |
| Feil et al. 2019 | 12 subacute | Randomized, double blind, sham-controlled | Bihemispheric tDCS | Left and Right IFG | 10 sessions with either tDCS or sham | Picture Naming, ANELT, AAT | Improved picture naming with bihemispheric tDCS compared to sham immediately after treatment, while ANELT and AAT scores improved at 4 weeks post treatment. |
| Marangolo et al. 2016 | 9 chronic | Randomized, double-blind, sham-controlled | Bihemispheric tDCS | Left and right IFG | 15 sessions with tDCS and 15 with sham | Word and syllable repetition, fMRI | Improved articulatory accuracy for treated and untreated stimuli for tDCS compared to sham. Furthermore, functional connectivity analysis revealed increased connectivity in the LH with tDCS but only in the RH with sham. |
| Manenti et al., 2015 | 1 chronic | Case study | Bihemispheric tDCS | Left and right DLPFC | 20 sessions with tDCS | Verb naming | Improved verb naming with treated and untreated items with bihemispheric tDCS. Improvements were maintained at 4, 12, 24, and 48 weeks post treatment. |
| Sebastian et al. 2017 | 1 chronic | Case study | Cerebellar tDCS | Right cerebellum | 15 sessions with tDCS and 15 sessions with sham | Spelling to Dictation and Written Picture Naming | Improved spelling for trained and untrained words, generalization to written picture naming immediately after and 2 months post-treatment with anodal cerebellar tDCS |
| Marangolo et al. 2018 | 12 chronic | Randomized double-blinded, sham controlled, cross over | Cerebellar tDCS | Right Cerebellum | 5 cathodal tDCS and 5 sham with verb naming, and 5 cathodal tDCS and 5 sham with verb generation | Verb Naming and Verb Generation | Improved verb generation with cathodal cerebellar tDCS compared to sham. |
| Shah-Basak et al. 2015 | 6 chronic | Randomized, sham-controlled, partial cross over | Anodal and Cathodal tDCS | Optimal tDCS montage. Anodal: Left or right frontal lobe, Cathode: Left or right frontal lobe, and Sham | 10 sessions with an optimal tDCS montage and 10 with sham | Picture naming | Improved picture naming with left-frontal cathodal-stimulation compared to sham. |
| Norise et al. 2017 | 9 chronic | Randomized, sham-controlled, partial cross over | Anodal and cathodal tDCS | Optimal tDCS montage Anodal: Left or right frontal lobe, Cathode: Left or right frontal lobe, and Sham | 10 sessions with an optimal tDCS montage and 10 with sham | Language fluency: BDAE Cookie theft | Severe baseline language profile was associated with larger improvements in fluency at the word-level after tDCS but not sham stimulation. These improvements were maintained at the 2-week follow-up. |
Abbreviations: tDCS: transcranial direct current stimulation; fMRI: functional magnetic resonance imaging; IFG: inferior frontal gyrus, BNT: Boston Naming Test; LH: Left hemisphere; RH: Right hemisphere; STG: superior temporal gyrus, EEG: electroencephalogram; ANELT: Amsterdam Nijmegen Everyday Language Test; AAT: Aachen Aphasia Test; BDAE: Boston Diagnostic Aphasia Examination