Researchers at the University of Queensland have found an association between Charles Bonnet Syndrome (CBS) and abnormally heightened activity in the visual cortex of the brain. The findings were published October 25, 2018 in the journal Current Biology.
According to the researchers, up to 40% of people with loss of vision experience hallucinations, which are thought to result from interrupted neural signals to the visual cortex (the part of the brain that interprets sight). Named after Charles Bonnet, who first studied the phenomenon in 1780, it was later defined as “persistent or recurrent visual pseudohallucinatory phenomena of a pleasant or neutral nature in a clear state of consciousness” (Damas-Mora, 1982). The hallucinations involve flashes of light, shapes, or geometric patterns and/or complex hallucinations, including faces, animals, or entire scenes.
The reason why some people experience CBS and others do not has been a mystery, but this study may have hit upon the answer. Exposing macular degeneration patients to various flickering images while performing a task using their peripheral visual fields, the researchers found that CBS individuals showed strikingly elevated visual cortical responses to peripheral field stimulation compared with patients without hallucinations. This offers direct support for the hypothesis of visual cortical hyperexcitability in patients with CBS.
Knowing that the syndrome is a neural, rather than a brain, disorder should relieve patients of unnecessary worry, which alone might help to reduce the frequency of the hallucinations and offer some comfort to the patient. Most important, it may give doctors a subjective means of diagnosing and treating CBS.
For an audio/visual presentation about Charles Bonnet syndrome, visit www.mdsupport.org/nsg/cbs/index.html