Discharging the voices: Non-invasive brain stimulation as a treatment for hallucinations

Abstract

Hallucinations are a common and disturbing symptom in psychotic disorders, among which auditory hallucinations are most frequently seen; 60 to 70% of patients with a schizophrenia spectrum disorder experience this type of hallucinations. These hallucinations are often in the form of negative and derogatory voices, and may contain insults, criticism, threats and commands. They may instigate violence and even suicide attempts. In approximately 75% of patients, the hallucinations can be sufficiently reduced with the use of antipsychotic medication. However, in the remaining 25%, the hallucinations persist despite optimal pharmacotherapy. For these patients, few other treatment options remain. The persistence of hallucinations in these patients remains burdensome and is of high impact on their quality of life. Finding an alternative treatment method that is able to reduce them is of high value. This collection of studies reports on the efficacy of two types of non-invasive brain stimulation (NIBS) as treatment methods for hallucinations. The focus is mainly on auditory hallucinations that are refractory to treatment with antipsychotic medication. Efficacy of one week theta burst rTMS treatment on the left temporoparietal junction was tested in comparison to placebo treatment. Furthermore, immediate effects of 1-Hz rTMS on the left and right temporoparietal junction on auditory hallucinations was tested compared to an occipital control location, as well as the neuronal effects of this treatment as measured by electroencephalography (EEG). Unfortunately, these studies found no evidence of rTMS efficacy for treatment-resistant hallucinations in comparison with placebo. However, several responders were found, which led to wonder if the treatment is only effective in a specific subset of patients. In a combined dataset it was then uncovered that being of a younger age and of female gender were predictors for a positive response of auditory hallucinations to rTMS treatment. In another study, the effect of one week 2 mA tDCS treatment on auditory hallucinations was tested. Again, it was found that this treatment was not effective when compared to placebo treatment. However, some benefit of tDCS was found on visual hallucinations in a case study, which should be further tested in a larger group compared to placebo. For both rTMS and tDCS as treatments for hallucinations, results up till now are highly varying, with meta-analyses indicating modest, but positive effect sizes for rTMS, but not yet for tDCS. Future studies should focus on unravelling the neurobiological mechanisms underlying NIBS, and adapting treatment parameters and targeting methods accordingly. Furthermore, as it was found that younger age and female gender were predictors for a positive response to rTMS, future work might aim at identifying more patient characteristics that may help to predict for whom NIBS have higher chances of success. The results in the current thesis call for new strategies in using NIBS as a treatment method for hallucinations.