Network-Targeted Neuromodulation for Nicotine Dependence in Schizophrenia

This study proposes to test the hypothesis that the brain circuits most relevant to nicotine use in schizophrenia are distinct from pathways identified in nicotine-using people without psychosis. This study seeks to provide evidence that targeted stimulation of the Default Mode Network (DMN) leads to both altered network activity and a concomitant behavioral change in cue-induced craving and cognitive performance in individuals with schizophrenia and schizoaffective disorder, while targeted stimulation of the left dorsolateral prefrontal cortex (L DLPFC) leads to these changes in nicotine-using people without psychosis.

The investigators will test this hypothesis in a crossover design comparing 1) DMN-targeted continuous theta burst stimulation (cTBS) and 2) L DLPFC-targeted intermittent theta burst stimulation (iTBS). cTBS and iTBS are types of rTMS. cTBS has inhibitory effects and reduces functional connectivity, while iTBS is excitatory and increases connectivity (Huang et al. 2005). By applying cTBS to the DMN, a target that modulates craving in schizophrenia, the investigators expect DMN connectivity to decrease, thereby decreasing craving. Excitatory stimulation (e.g. iTBS) to the L DLPFC reduces craving in smokers without psychosis (Tseng et al. 2022).

This study will test a model that integrates brain network pathophysiology and cognition to 1) explain the prevalence of nicotine use in schizophrenia and 2) identify a target for engagement in schizophrenia. This study seeks to establish a neuroscientific framework to guide future treatment-oriented studies aimed at reducing craving and improving cognitive performance in individuals with schizophrenia and schizoaffective disorder.

Aim 1: Target Engagement: Determine if rTMS manipulates functional connectivity of each target (DMN, L DLPFC) (n=60). Hypothesis 1A: Functional connectivity of the entire DMN will decrease after 5 days of DMN-targeted cTBS. Hypothesis 1B: Functional connectivity of the L DLPFC to the left insula will increase after 5 days of L DLPFC-targeted iTBS. As an exploratory hypothesis, the investigators will test if there is an effect of diagnosis on connectivity change.

Aim 2: Clinical Efficacy: Determine if rTMS affects cue-induced craving and if craving change correlates with change in functional connectivity (n=60). Hypothesis 2A: Both DMN-targeted and L DLPFC-targeted rTMS will significantly reduce craving. Hypothesis 2B: Craving change will be correlated with functional connectivity change. As an exploratory hypothesis, in individuals with schizophrenia, DMN-targeted cTBS will be more efficacious than L DLPFC-targeted iTBS.