Improvement of Insight with Non-Invasive Brain Stimulation in Patients with Schizophrenia: A Systematic Review.

Martin Blay,Rémy Bation,Jérôme Brunelin,Filipe Galvao,Ondine Adam,Marine Mondino

doi:10.3390/jcm11010040

Abstract

Patients with schizophrenia are often unaware of their condition and the consequences of their illness. This lack of insight results in impaired functioning, treatment non-adherence and poor prognosis. Here, we aimed to investigate the effects of non-invasive brain stimulation (NIBS) on two forms of insight, clinical and cognitive, in patients with schizophrenia. We conducted a systematic review of the literature registered in the PROSPERO database (CRD42020220323) according to PRISMA guidelines. The literature search was conducted in Medline and Web of Science databases based on studies published up until October 2020 that included pre-NIBS and post-NIBS measurements of clinical and/or cognitive insight in adults with schizophrenia. A total of 14 studies were finally included, and their methodological quality was assessed by using the QualSyst tool. Despite the lack of well-conducted large randomized-controlled studies using insight as the primary outcome, the available findings provide preliminary evidence that NIBS can improve clinical insight in patients with schizophrenia, with a majority of studies using transcranial direct current stimulation with a left frontotemporal montage. Further studies should investigate the effect of NIBS on insight as a primary outcome and how these effects on insight could translate into clinical and functional benefits in patients with schizophrenia.

Highlights

Schizophrenia is a severe psychiatric disorder affecting 20 million people worldwide [1] and is associated with poor functional, social and professional outcomes, and with increased early mortality [2]
Almost all selected studies found a significant increase in clinical insight following repeated sessions of non-invasive brain stimulation (NIBS) in this population, with some studies even reporting a maintenance of the effect for at least 3 months
Given that the review was designed to provide a comprehensive overview of the existing literature on the effects of NIBS on insight in schizophrenia and given the limited data available on this subject, we chose to include case reports and a case series, which limits the generalization of the findings reported here

Summary

Introduction

Schizophrenia is a severe psychiatric disorder affecting 20 million people worldwide [1] and is associated with poor functional, social and professional outcomes, and with increased early mortality [2]. One of the core features of schizophrenia is the lack of insight into the illness, i.e., the lack of awareness of having a mental disorder, of its symptoms and of its consequences, which is observed in 50% of patients with schizophrenia [4,5] This feature has been shown to be linked to several cognitive functions, including the theory of mind [6]. Cognitive insight involves two subcomponents: the capacity for self-reflectiveness and the capacity to resist excessive self-certainty [13,14,15] This form of insight is thought to be related to specific brain regions: the hippocampal neural efferent pathway being involved in self-certainty [16] and the prefrontal (especially its ventrolateral part) and temporal cortical regions being involved in self-reflectiveness [17]. They are thought to be different constructs, the different forms of insight are intimately correlated, and cognitive insight is sometimes seen as prerequisite for clinical insight [13,18]

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