Table 1.
Detailed study characteristics and participant demographics of included tDCS trials.
| Author, year | Outcome assessment measures | Duration of intervention | Location of study | tDCS protocol (active treatment arm) | Anode placement site | No. of participant | Age (years) | Clinical profile of participants |
|---|---|---|---|---|---|---|---|---|
| Zhou et al., 2023 (Zhou et al., 2023) | Cambridge Neuropsychological Test Automated Battery | 5 weeks | China | 15 sessions of 2 mA continuous, direct current on weekdays of the 1st, 3rd, and 5th week | Left Prefrontal Cortex | Active:21 Sham:17 | 18–70 (chronic schizophrenia with TD) | Chronic schizophrenia (1-year cumulative antipsychotic use) with Tardive Dyskinesia. |
| Lisoni et al., 2022 (Lisoni et al., 2022) | Brief Assessment of Cognition in Schizophrenia | 3 weeks | Italy | 15 sessions of 2 mA continuous, direct current on weekdays |
Left Dorsolateral Prefrontal Cortex | Active: 25 Sham: 25 |
≥ 18 | Schizophrenia stabilized after at least one month of antipsychotic treatment. |
| Bulubas et al., 2021 (Bulubas et al., 2021) | 1. Penn-CNB 2. Penn Conditional Exclusion Test 3. Penn Letter N-Back test (PLNB) 4. Penn Word Memory Test (PWMT), 5. Penn Face Memory Test (PFMT), 6. Short Visual Object Learning Test (volt) 7. Emotion identification (EMI) |
5 days | Brazil | 10 sessions of 20 min 2 mA continuous, direct current two times per day over the course of one week. Monday to Friday, with inter-session intervals between 180 and 210 min |
Left Prefrontal Cortex | Active:48Sham:42 | 18–55 | Schizophrenia with prominent negative symptoms and stable positive and negative symptoms, with a stable antipsychotic dose for 4 weeks at enrollment. . |
| Chang et al., 2020 (Chang et al., 2020) | 1. Mini-Mental State Examination 2. The Trail Making Test 3. Wisconsin Card Sorting Test 4. Tower of London-Drexel University Test (TOLDXtm 2nd edition) |
5 days | Taiwan | 10 sessions of 20 min 2 mA continuous direct current twice daily, 5 consecutive weekdays with inter-session intervals >2 h | Bilateral Dorsolateral Prefrontal Cortex | Active:30 Sham: 30 |
20–65 | Schizophrenia or schizoaffective disorder, illness duration ≥1 year, stable on antipsychotics but symptomatic for ≥4 weeks (CGI-S ≤ 4). |
| Smith et al., 2020 (Smith et al., 2020) | 1. Repeatable Battery for the Assessment of Neuropsychological Status 2. MATRICS™ Consensus Cognitive Battery (MCCB™) |
10–17 days | China | 10 sessions of 20 min 2 mA continuous direct current stimulation. | Left Dorsolateral Prefrontal Cortex | Active:24 Sham: 25 |
19–60 | Schizophrenia stabilized on medications with no recent acute exacerbation of symptoms, but still with significant cognitive deficit. |
| Weikert et al., 2019 (Weickert et al., 2019) | 1. Weschler Test of Adult Reading (WTAR) 2. Wechsler Adult Intelligence Scale 3rd Edition (WAIS-III) 3. MATRICS™ Consensus Cognitive Battery (MCCB™) |
4 weeks | USA | 20 sessions of 20 min 2 mA continuous direct current stimulation. | Right Dorsolateral Prefrontal Cortex | Active:6 Sham:6 |
18–50 | Patients with schizophrenia or schizo-affective disorder on antipsychotics for at least one year. |
| Jeon et al., 2018 (Jeon et al., 2018) | MATRICS™ Consensus Cognitive Battery (MCCB™) | 10 days | Rep of Korea | 30 mins of active 2 mA tDCS | Left & Dorsolateral Prefrontal Cortex | Active:28 Sham:28 |
18–65 | Patients with schizophrenia clinically stable for at least 3 months. |
| Gomes et al., 2018 (Gomes et al., 2018) | MATRICS™ Consensus Cognitive Battery (MCCB™) | 3 months (10 days intervention and then one assessment at 3 months) |
Brazil | 10 sessions of 20 min 2 mA continuous direct current stimulation. two consecutive weeks (Monday to Friday) |
Left Dorsolateral Prefrontal Cortex | Active:12 Sham:12 |
18–65 | Patients with schizophrenia stable on medication for at least 6 weeks, no co-morbid substance use disorder. |
| Smith et al., 2015 (Smith et al., 2015) | MATRICS™ Consensus Cognitive Battery (MCCB™) | 10–12 days | USA | 5 sessions of 20 min 2 mA continuous direct current stimulation. |
Left Dorsolateral Prefrontal Cortex | Active:19 Sham:18 |
≥18 years | Patients with schizophrenia or schizo-affective disorder and regular cigarette smokers. |
| Lindenmayer et al. 2019 (Lindenmayer et al., 2019) | MATRICS™ Consensus Cognitive Battery (MCCB™) | 4 weeks | USA | 40 sessions of 2 mA for 20 min session, twice daily for four weeks | Left Dorsolateral Prefrontal Cortex | Active:15 Sham:13 | 18–65 | Patients with long-standing treatment resistant schizophrenia and persistent auditory hallucination. |
| Mellin et al. 2018 (Mellin et al., 2018) |
1. Cognitive function (BACS) 2. Brief assessment of cognition in schizophrenia (BACS) |
5 days | USA | 10 sessions of 2 mA for 20 min session, twice daily | Left Dorsolateral Prefrontal Cortex | Active:7 Sham:7 | Mean age 29.57 (10.97) for tDCS And 38.86 (10.01) for sham |
Clinically stable patients with schizophrenia. |
| Koops et al. ., 2018 (Koops et al., 2018) | Stroop test and trail making test | 5 days | Netherland | 10 sessions of 2 mA for 20 min session, twice daily. | Left Dorsolateral Prefrontal Cortex | Active: 28 Sham:26 |
≥18 | Participants had daily auditory hallucinations, were resistant to two antipsychotics, and were on a stable dose for at least two weeks before study entry. |
| Palm et al. 2016 (Palm et al., 2016) | 1.Self-Ordered Pointing Task (SOPT) for WM, 2. Trail-Making Test (TMT-A) for processing speed, and TMT-B for executive functioning. |
5 days | Germany | 10 sessions of 2 mA for 20 min session, twice daily | Left Dorsolateral Prefrontal Cortex | Active: 10 Sham:10 |
18–65 | Patients with predominant negative symptoms a PANSS score > 70, and stable antipsychotic treatment for over 4 weeks. |