Charles Bonnet Syndrome


Among the many types of visual hallucination is a condition known as Charles Bonnet Syndrome. Oliver Sacks describes a number of cases in which people suffer these detailed visual hallucinations despite having some degree of visual impairment. These hallucinations can be of geometric patterns, places, objects, or people. Typically, the afflicted does not recognise the people appearing in the hallucinations, nor does there seem to be any meaning or real world connection to the figures, actions, or locations in the hallucinations. They are described as being like a "silent movie", and not fading in and out but rather appearing and disappearing suddenly. The emergence of these hallucinations can lead otherwise sane and normal people to believe that they are going insane, which is naturally a source of much distress.

Sacks describes the case of one woman who, at 95, was completely blind from macular degeneration. Sacks tells how she hallucinated pink and blue squares on the floor and walls, which develop into processions of people in ‘Eastern dress’, people with deformed faces, hallucinations of children in bright colours walking up and down stairs, and visions of a horse ploughing snow. While the woman was aware that visions were only hallucinations, she was still very much disturbed and frightened by them.

Charles Bonnet syndrome (CBS) is named for Charles Bonnet, whose grandfather suffered from hallucinations involving a large blue handkerchief and a wheel, both floating in the air. These were obvious hallucinations. Often times, however, it was not easy for his grandfather to discern between hallucination and reality, as he once hallucinated that his granddaughter was accompanied by two handsome young men, and when inquiring as to the who the men were, his granddaughter replied that she was in fact not accompanied by anyone, and then the two young men disappeared. This sudden disappearance is typical of Charles Bonnet syndrome hallucinations.

Sacks also describes a number of hallucinations experienced by other sufferers of CBS. These include visions of figures that split into multiple beings and then recombine into one, reoccurring objects (based on reality) that appear in incongruous places, and hallucinations of cartoons. Thus, the hallucinations characterised by CBS are often not related to the sufferer’s life experiences, relationships, or interests.

This item was chosen because, as Sacks mentions, these types of hallucinations are not uncommon, and also for the simple reason that CBS is quite interesting as students of neuroscience. Sacks mentions that CBS hallucinations may be similar to dreaming in the way that they occur within the brain – a neuroscientific hypothesis called activation synthesis theory. That is, as one loses vision and the visual parts of the brain are no longer getting any input, they become hyperactive and excitable, so they begin to fire randomly and one experiences hallucinations. This is fascinating to us both as regular people who dream, and as students exploring the functions and mechanisms of the brain.