Stimulus-Driven Cortical Hyperexcitability in Individuals with Charles Bonnet Hallucinations

Abstract

Highlights d Individuals with age-related macular degeneration can develop visual hallucinations d Visual cortical hyperexcitability may cause hallucinations d We measured cortical excitability using frequency-tagged visual stimulation d Individuals with hallucinations showed hyperexcitability relative to controls

The elephant in the room: understanding the pathogenesis of Charles Bonnet syndrome

“…How a reduction in sensory input to the relevant parts of the cortex results in hallucinatory experiences is unclear. One option is that some individuals are prone to cortical hyperexcitability, leading to visual perceptions. Alternatively, it has been proposed that abnormal neuronal activity in the visual brain is usually suppressed by sensory input, but brought to the fore when this input is reduced in the visually impaired, resulting in complex hallucinations .…”

Charles Bonnet Syndrome: Cortical Hyperexcitability and Visual Hallucination

“…Perhaps, then, the hyperexcitability of visual cortex in Charles Bonnet syndrome patients reported by Painter et al [1] is itself heterogeneous, with different regions of visual cortex being hyperexcitable in different Charles Bonnet syndrome patients. As Painter et al [1] point out, this question could not be examined in their study because of the poor spatial resolution of electroencephalography (EEG). When EEG data were averaged across all 12 patients, there was evidence of widespread excitability, but that is consistent with different patients having different localized regions of chronic hyperexcitability.…”

“…About 40% of people with an ocular pathology, typically macular degeneration, that leads to loss of foveal vision with preservation of peripheral vision develop a visual-hallucinatory condition known as Charles Bonnet syndrome. As they report in this issue of Current Biology, Painter et al [1] have compared electrophysiological responses to peripheral visual field stimulation in people with macular degeneration who experience visual hallucinations, people with macular degeneration who do not experience visual hallucinations, and healthy controls. The hallucinatory group showed much stronger visual cortical responses to peripheral stimulation compared to the other two groups.…”

“…The nature of Charles Bonnet syndrome can be appreciated by inspecting Table S1 of the Painter et al [1] paper, which describes the contents of the visual hallucinations experienced by each of the 8 subjects in the study. Some of the subjects experienced meaningless visual patterns, for example: ''Black squiggles in the left periphery, moving and chasing each other, like very thin worms or snakes''.…”

“…This leads to a second issue, which concerns the consistency of the hallucinatory contents. Painter et al's [1] patient 3 reported that his hallucinations took the form of ''a head of a brown lion''. Was it the case that every time he experienced a visual hallucination it always took this exact form?…”