Visual Hallucinations in Psychosis: The Curious Absence of the Primary Visual Cortex.

BACKGROUND AND HYPOTHESIS

Approximately one-third of patients with a psychotic disorder experience visual hallucinations (VH). While new, more targeted treatment options are warranted, the pathophysiology of VH remains largely unknown. Previous studies hypothesized that VH result from impaired functioning of the vision-related networks and impaired interaction between those networks, including a possible functional disconnection between the primary visual cortex (V1) and higher-order visual processing regions. Testing these hypotheses requires sufficient data on brain activation during actual VH, but such data are extremely scarce.

STUDY DESIGN

We therefore recruited seven participants with a psychotic disorder who were scanned in a 3 T fMRI scanner while indicating the occurrence of VH by pressing a button. Following the scan session, we interviewed participants about the VH experienced during scanning. We then used the fMRI scans to identify regions with increased or decreased activity during VH periods versus baseline (no VH).

STUDY RESULTS

In six participants, V1 was not activated during VH, and in one participant V1 showed decreased activation. All participants reported complex VH such as human-like beings, objects and/or animals, during which higher-order visual areas and regions belonging to the vision-related networks on attention and memory were activated.

DISCUSSION

These results indicate that VH are associated with diffuse involvement of the vision-related networks, with the exception of V1. We therefore propose a model for the pathophysiology of psychotic VH in which a dissociation of higher-order visual processing areas from V1 biases conscious perception away from reality and towards internally generated percepts.