Table 1.

Studies using tDCS for the treatment of auditory hallucinations (AH).

Reference	Design	Patients	Position of electrodes	Current strength	Duration	Effects
Andrade (2013)	Case study	One subject with schizophrenia and clozapine resistant AH.	The cathode over the left temporoparietal cortex (TPC) and the anode over the left dorsolateral prefrontal cortex (DLPFC).	First 1 mA, later 3 mA	First 20 min (daily sessions for 2 consecutive months), later 30 min (twice daily sessions for 3 consecutive years).	A reduction of 90% in AH severity was reported after the first 2 months. After increasing treatment to twice daily and a current intensity of 3 mA, AH severity further improved. When electrode positioning was changed or treatment frequency was reduced to once per 2 days, the ameliorating effects disappeared.
Bose et al. (2014)	Open label study, without a placebo condition	21 subjects with schizophrenia and medication resistant AH.	The cathode over the left TPC and the anode over the left DLPFC.	2 mA	20 min (twice daily sessions on 5 consecutive days).	Improvement of 32% in AH severity.
Brunelin et al. (2012)	Randomized, placebo controlled, double-blind trial	30 subjects with schizophrenia and medication resistant AH.	The cathode over the left TPC and the anode over the left DLPFC.	2 mA	20 min (twice daily sessions on 5 consecutive days).	Improvement of 31% in AH severity which lasted for 3 months.
Fitzgerald et al. (2014)	Randomized, placebo controlled, double-blind trial	24 subjects with schizophrenia or schizoaffective disorder and medication resistant AH.	Unilateral and bilateral tDCS with the cathode over the (left) TPC and the anode over the (left) DLPFC.	2 mA	20 min (daily sessions on 15 days in 3 consecutive weeks)	AH did not respond to either treatment method, and no difference was found between the active and placebo treatment group.
Homan et al. (2011)	Case study	One subject with schizophrenia and medication resistant AH.	The cathode over the left TPC and the anode over the right supraorbital area.	1 mA	15 min (daily sessions on 10 consecutive days)	Amelioration of AH was reported, which was still present 6 weeks after treatment.
Mondino et al. (2014)	Randomized, placebo controlled, double-blind trial	28 subjects with schizophrenia and medication resistant AH.	The cathode over the left TPC and the anode over the left DLPFC.	2 mA	20 min (twice daily sessions on 5 consecutive days).	Improvement of 46% in AH severity in the active treatment group, with no such effect in the placebo group.
Nawani et al. (2014)	Case study	One subject with schizophrenia and medication resistant AH.	The cathode over the left TPC and the anode over the left DLPFC.	2 mA	20 min (twice daily sessions on 5 consecutive days).	Improvement of AH.
Rakesh et al. (2013)	Case study	One subject with schizophrenia and medication resistant AH.	The cathode over the left TPC and the anode over the left DLPFC.	2 mA	20 min (twice daily sessions on 5 consecutive days).	Complete cessation of AH.
Shiozawa et al. (2013)	Case study	One subject with schizophrenia and medication resistant AH.	The cathode over the left TPC and the anode over the left DLPFC.	2 mA	20 min (twice daily sessions on 5 consecutive days).	Improvement of AH, which was sustained after a 2-month follow-up.
Shivakumar et al. (2013)	Case study	One subject with schizophrenia and medication resistant AH.	The cathode over the left TPC and the anode over the left DLPFC.	2 mA	20 min (twice daily sessions on 5 consecutive days).	Complete cessation of AH, which was sustained after a 4-week follow-up.