# Altered Effective Connectivity Within a Thalamocortical Corollary Discharge Network in Individuals With Schizophrenia

## TL;DR

This study shows that people with schizophrenia have altered brain connectivity in a network involved in eye movement planning, which may explain their passivity and self-experience issues.

## Contribution

The study identifies reduced thalamus-to-IPS connectivity in schizophrenia and links it to passivity symptoms using dynamic causal modeling.

## Key findings

- Effective connectivity from thalamus to IPS was reduced in individuals with schizophrenia.
- Reduced connectivity correlated with the severity of passivity symptoms in schizophrenia.
- The DS task modulated network connectivity, highlighting the role of CD signaling in the network.

## Abstract

Sequential saccade planning requires corollary discharge (CD) signals that provide information about the planned landing location of an eye movement. These CD signals may be altered among individuals with schizophrenia (SZ), providing a potential mechanism to explain passivity and anomalous self-experiences broadly. In healthy controls (HC), a key oculomotor CD network transmits CD signals from the thalamus to the frontal eye fields (FEF) and the intraparietal sulcus (IPS) and also remaps signals from FEF to IPS.

Here, we modeled fMRI data using dynamic causal modeling (DCM) to examine patient-control differences in effective connectivity evoked by a double-step (DS) task (30 SZ, 29 HC). The interrogated network was formed from a combination of (1) functionally identified FEF and IPS regions that robustly responded on DS trials and (2) anatomically identified thalamic regions involved in CD transmission. We also examined the relationship between clinical symptoms and effective connectivity parameters associated with task modulation of network pathways.

Network connectivity was indeed modulated by the DS task, which involves CD transmission. More importantly, we found reduced effective connectivity from thalamus to IPS in SZ, which was further correlated with passivity symptom severity.

These results reaffirm the importance of IPS and thalamocortical connections in oculomotor CD signaling and provide mechanistic insights into CD alterations and consequently agency disturbances in schizophrenia.