Cerebro-cerebellar circuitry in the pathophysiology of auditory hallucinations: dysmetria of auditory perceptual processing?

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PROJECT SUMMARY/ABSTRACT This R21 proposal aims to provide detailed understanding of how finely parcellated subareas of the auditory cortex (AC) are functionally connected with one another and with cerebellar regions in schizophrenia (SZ) patients with auditory hallucinations (AH). AH can be disabling, and do not always respond to existing treatments. A clear understanding of AH pathophysiology is needed to guide the development of more effective treatments for AH, but such knowledge is currently lacking. Previous research suggests that the AC is abnormal in AH, suggesting a possible perceptual basis for AH. The AC, however, is one of many brain regions implicated in AH pathogenesis, and a better understanding of how AC interacts with other critical brain areas is needed. The cerebellum coordinates a host of cerebral cortical functions—including higher-level cognitive, affective, and perceptual processes—rather than just motor functions, as traditionally believed. Consistent with this framework, the myriad symptoms of psychosis have been proposed to reflect “dysmetria,” or incoordination, of mental activity due to disruptions in cerebro-cerebellar circuits (Andreasen, et al., 1996; Schmahmann, 1998). Given evidence that the cerebellum is reciprocally connected to AC and coordinates auditory processing, there is motivation to understand how abnormal AC-cerebellar circuitry might lead to `auditory dysmetria', and AH. We propose to examine features of local AC circuitry and AC-cerebellar circuitry underlying AH by utilizing an innovative and highly reliable AC parcellation strategy based on resting state functional magnetic resonance imaging (rsfMRI). This parcellation method, which computes functional connectivity (FC) between voxels in AC and the rest of the brain, will be used to segment AC into multiple subareas. Subdividing the AC at this fine- grained a level could only be achieved before with postmortem (e.g., cytoarchitectonic) methods. Here, these individual-specific and functionally defined AC subareas will serve as the seeds for FC between AC subareas and between AC and cerebellum. Our aims are to identify features of AC inter-subarea FC (Aim 1) and features of AC-cerebellar FC (Aim 2) that track with AH severity in SZ. We also aim to validate how these markers change with intra-subject variations in AH (Aim 3), using data from an independent interventional longitudinal study. Our hypotheses are two-fold: (1) The AC is comprised of a complex local network of both primary sensory and association subareas, and FC between AC subareas is meaningfully associated with AH. (2) The cerebellum plays a key role in coordinating activity in AC subareas, and this process is `dysmetric' in AH. This project is significant because it is the first step in a continuum of research that is expected to lead to the development of more targeted and personalized treatments for AH. Repetitive transcranial magnetic stimulation (rTMS) is a promising non-pharmacological treatment for AH. We propose that stimulation of cerebellar regions that are connected to association subareas of AC may provide access to circuits that are dysmetric in AH. We expect that this proposal will identify potential cerebellar targets for rTMS that can be tested in a future clinical trial.