Visual cortical activity in Charles Bonnet syndrome: testing the deafferentation hypothesis

Area of Science:

• Neuroscience
• Ophthalmology
• Psychiatry

Background:

• Charles Bonnet syndrome (CBS) involves visual hallucinations after sight loss.
• The underlying neurophysiology of CBS is not fully understood.
• The deafferentation hypothesis suggests compensatory neural activity in the visual cortex.

Purpose of the Study:

• To investigate visual cortical activity in individuals with CBS.
• To compare neurophysiological markers between CBS patients and controls with eye disease.
• To explore the relationship between visual cortex excitability and hallucination severity.

Main Methods:

• Multi-modal investigation using functional MRI, EEG, and TMS.
• Compared 19 individuals with CBS to 18 matched individuals with eye disease but no hallucinations.
• Assessed visual cortical activity, EEG alpha-reactivity, and TMS phosphene thresholds.

Main Results:

• Individuals with CBS showed reduced BOLD activation and EEG alpha-reactivity in the visual cortex.
• The CBS group exhibited increased occipital theta power, indicating cortical slowing.
• Reduced visual activation correlated with increased cortical excitability (lower TMS phosphene thresholds) and hallucination severity.

Conclusions:

• Findings support the role of increased visual cortical excitability in CBS.
• Results align with the deafferentation hypothesis for visual hallucinations post-sight loss.
• Suggests a neurophysiological basis for visual hallucinations in some individuals with acquired vision impairment.