Via Andrew Sullivan, I learned that Oliver Sacks has a new book out, Hallucinations. The video above is a 2009 TED talk in which he discusses Charles Bonnet syndrome, the focus of his book. There’s also a very interesting article about Dr. Sacks in last week’s New York Magazine and another good interview with him here.
I actually have an elderly acquaintance who may have a variant of Charles Bonnet. He has significant hearing impairment and recently developed nighttime auditory hallucinations. They consist of a voice saying “Goodbye–have a nice day!” He’s gone so far as to replace all of the cordless phones in his house on the theory that they are picking up stray radio signals. He set up a tape recorder in an attempt to capture the voices, without luck.
He seems to have mild cognitive impairment but is not obviously demented. He did have an episode of post-operative delirium that was characterized by normal consciousness but an elaborate delusion that strangers had set up a movie studio in his house.
When my acquaintance asked for an informal opinion about his auditory problem, I suggested that both symptoms might be manifestations of mild cognitive decline–his brain functions relatively well most of the time but under the right conditions, especially the stress of anesthesia and surgery, otherwise well-compensated neuropsychiatric problems arise.
After listening to Dr. Sacks’s talk, it occurs to me that the auditory hallucinations could be a variant of Charles Bonnet syndrome. A brief literature review shows that this has been described and that the manifestations are usually musical. It doesn’t seem to far-fetched, however, to suggest that they could just as easily be vocal.
Even more interesting, and bringing the argument full circle, is the hypothesis that Charles Bonnet syndrome itself may be a marker of incipient dementia. Perhaps the predisposition to hallucination resulting from sensory impairment is held in check by people with young, healthy brains, but those with poor “cerebral reserve” are unable to do so. In other words, the problem may be “multifactorial”, as is so often the case in neurology.