NIBS in addiction: Neurobiological mechanisms and clinical outcomes

Addiction is correlated with the dysfunction of definite neural circuitry involving deep as well as superficial brain regions. Among the deep structures are the midbrain ventral tegmental area (VTA) and the nucleus accumbens of the ventral striatum, connected to each other by means of dopaminergic fibers. This pathway is the neural correlate of normal appetitive behaviour and is part of the reward system. Cortical areas such as the dorsolateral prefrontal cortex (DLPFC) exert an inhibitory control over the appetitive behaviours through descending cortico-striatal projections. Non–invasive brain stimulation (NIBS) of these regulatory cortical areas has been shown to modify symptoms of substance use disorders and behavioural addictions in several recent studies. In particular, repetitive Transcranial Magnetic Stimulation (rTMS) over the left DLPFC was shown to be effective in reducing relapse in abstinent tobacco smokers while it did not consistently reduce craving and consumption in current smokers. Moreover, in cocaine-use disorder, craving, substance consumption and anhedonia were found to be reduced by the application of rTMS over the right and/or left DLPFC. Preliminary data also point to a possible role of rTMS in the treatment of non-substance addictive behaviours, such as gambling disorder. In recent years, another promising NIBS technique, i.e. transcranial direct current stimulation (tDCS) was used to reduce the symptoms of various addictive disorders, with mixed results. In conclusion, the growing evidence of NIBS efficacy for the treatment of addictive disorders does warrant further larger-scale randomized controlled studies.