Biological basis for visual hallucinations identified

Visual hallucinations in patients with schizophrenia may be caused by hyperconnectivity in a specific area of the brain, say researchers.

“While [visual hallucinations] are generally neglected in clinical assessments in this population, functional connectivity data provide biological support for their distressing reality”, says the team, led by Judith Ford (San Francisco VA Medical Center, California, USA).

Ford and colleagues studied 180 schizophrenia patients, and found that the 45 who had experienced visual hallucinations in the month prior to brain imaging had hyperconnectivity between the amygdala and the visual cortex, relative to 178 mentally healthy controls matched for age, gender, handedness and ethnicity.

“This hyperconnectivity may facilitate retrieval and reactivation of visual memories, arguably the raw material of [visual hallucinations]”, the team writes in Schizophrenia Bulletin.

Patients with visual hallucinations also had significantly increased connectivity relative to 50 patients with auditory hallucinations and 67 without any visual or auditory hallucinations. The connectivity was strongest for Brodmann area (BA)18, and tended to be stronger for right than left BA18 connectivity.

Of note, connectivity between the amygdala and BA18 was significantly stronger in patients with visual hallucinations than auditory hallucinations for both the right and left hemispheres.