Low-Intensity Focused Ultrasound Neuromodulation of the Mediodorsal Thalamus for Treatment-Resistant Schizophrenia

Approximately 30% of patients with schizophrenia have symptoms that persist despite multiple antipsychotic medication trials including clozapine, and there is currently no evidence-based treatment option for this population. These patients often suffer psychological distress related to their psychotic symptoms, become chronically disabled, and are unable to lead meaningful lives. Several promising new treatment modalities are being explored including deep brain stimulation (DBS) in subjects with treatment-resistant schizophrenia. A pilot study at another institution is using DBS of the substantia nigra pars reticulata (SNr) to modulate circuitry in the thalamus by disinhibiting the mediodorsal (MD) nucleus of the thalamus. This approach follows evidence from multiple structural and functional studies implicating hypofunction of the MD thalamus in the pathophysiology of schizophrenia. This includes an association between MD hypofunction and both positive and cognitive symptoms of schizophrenia including auditory hallucinations and working memory, respectively. As DBS is an invasive neurosurgical procedure with small but definable risks of neurologic injury, a minimally invasive screening method to optimize patient selection for DBS would be optimal. This pilot study aims to investigate the use of MRI-guided low-intensity focused ultrasound (LIFU) to modulate neuronal activity within the thalamus in human subjects with treatment-resistant schizophrenia. Focused ultrasound itself is a safe, incisionless technology with high spatial resolution and depth penetration that has been shown to stimulate and inhibit neuronal activity. At high intensities, focused ultrasound can be used to thermally ablate a specific region of brain tissue and has been FDA-approved for the treatment of essential tremor and tremor in Parkinson's disease via thermal ablation of the ventral intermediate (VIM) thalamus. In contrast, LIFU is non-ablative and thus can be used for transient neuromodulation with high spatial precision due to direct real-time MRI targeting. This pilot study aims to use non-ablative LIFU to target the MD thalamus noninvasively and specifically, with the aim of interrogating and modulating the neuronal circuitry involved in symptoms of schizophrenia.