![]() ![]() In other words, the hallucinations were not the result of external stimuli (such as sensory images or instructions from the research team), but were instead evoked internally by the slow, spontaneous, brain activity fluctuations. But in the group with Charles Bonnet syndrome, the scientists observed a gradually increasing wave of activity, reminiscent of the slow spontaneous fluctuations, that emerged just before the onset of the hallucinations. In both the sighted participants and those in the imagery group, the activity took place in response either to visual input or to the instructions set in the task. ![]() The same visual areas in the brain were active in all three groups – those that hallucinated, those that watched the films and those creating imagery in their minds’ eye.īut the researchers noted a difference in the timing of the neural activity between these groups. Another control group, consisting of blind people who had lost their sight but did not experience visual hallucinations, was asked to imagine similar visual images while in the scanner. The scientists then created movies based on the participants’ verbal descriptions, and they showed these movies to a sighted control group, also inside an fMRI scanner. These participants’ brain activity was measured using an fMRI scanner while they described their hallucinations as they occurred. The researchers first invited to their lab five people who had lost their sight and reported occasionally experiencing clear visual hallucinations. This is because in Charles Bonnet syndrome, the hallucinations appear at random, in a truly unprompted fashion, and the visual centres of the brain do not process outside stimuli (because these individuals are blind), and are thus activated spontaneously. People experiencing Charles Bonnet visual hallucinations presented the research team with a rare opportunity to investigate their hypothesis. The research team was seeking to understand whether unprompted behaviours, that occur without any external cause, might be triggered by these spontaneous brain fluctuations. The researchers were studying slow, spontaneous fluctuations, which appear unconsciously in our brains when we rest. The study, published in Brain, investigated why some people who have lost their eyesight experience vivid hallucinations, a condition called Charles Bonnet syndrome. ![]() Visual hallucinations in people who have lost their sight can stem from spontaneous activity in the brain’s visual centres, according to a study led by UCL and Weizmann Institute of Science researchers. ![]()
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