Neuroimaging studies in patients with Charles Bonnet Syndrome

Charles Bonnet Syndrome (CBS) is characterized by complex formed and recurrent visual hallucinations in psychologically normal people, and is often associated with eye pathology. Many psychiatrists have taken an interest in CBS because this syndrome could provide clues to the mechanisms underlying visual hallucinations. In the present paper, we review previous neuroimaging studies in patients with CBS and summarize the results of these studies. There could be a fundamental dysfunction in the primary and secondary visual cortices in some patients with CBS, and transient cortical activation occurs in the inferior lateral temporal cortex during the appearance of visual hallucinations in CBS patients. External visual stimuli are perceived in the retina and are transmitted to the primary visual cortex (Brodmann area (BA) 17). The stimuli are transmitted from BA 17 to the secondary visual cortex (BA 18) and then to the visual association cortices (BA 19 and BA 37). In general, our perception of external visual stimuli normally has an inhibitory effect on the endogenous activation of the visual cortex. Visual loss due to certain conditions, of which eye pathology is the most commonly postulated in CBS patients, produces a state of sensory deprivation that releases the visual cortex from regulation by external stimuli, resulting in visual hallucinations (cortical release phenomenon). The results of previous neuroimaging studies suggest that the cortical release phenomenon hypothesis for the occurrence of visual hallucinations in patients with CBS is plausible. In addition, the results indicate that not only eye pathology, but also dysfunction in the primary and secondary visual cortices could result in deprivation of external visual stimuli.