Scientists at the Weizmann Institute of Science have found what they say might be the cause of "Charles Bonnet syndrome," a phenomenon in which blind people continue to "see" due to vivid visual hallucinations. The research also indicated that the same visual system that humans use to see is active when humans hallucinate or even imagine.
The findings, published in the journal Brain, show a mechanism which may enable normal activity in the brain's vision centers to trigger the hallucinations in the blind. Researchers revealed a connection between resting-state brain fluctuations - mysterious but common brain occurrences which happen when humans are not conscious - and visual hallucinations in the blind.
It is difficult to investigate brain fluctuations due to the the difficulty in separating them from other brain activity and it is hard to induce spontaneous activity without rendering it un-spontaneous. Individuals with Charles Bonnet experience purely spontaneous fluctuations, because these fluctuations cannot be stimulated visually in blind people, and so they afforded researchers an opportunity to examine them.
Through fMRI scans of people with Charles Bonnet syndrome and scans of a sighted control group shown videos made by researchers which were based on descriptions of the hallucinations experienced by the Charles Bonnet group, the researchers were able to identify brain fluctuations in the Charles Bonnet group.
“Our research clearly shows that the same visual system is active when we see the world outside of us, when we imagine it, when we hallucinate, and probably also when we dream,” says Prof. Rafi Malach. “It also exemplifies the creative power of vision and the contribution of spontaneous brain activity to unprompted and creative behaviors,” he adds.
Dr. Meytal Wilf of Lausanne University Hospital, Dr. Boris Rosin of the Ophthalmology Departments of Hadassah-University Medical Center and University of Pittsburgh Medical Center, and Prof. Marlene Behrmann of Carnegie Mellon University also participated in the research.
