Transcranial Direct Current Stimulation in the Treatment of Visual Hallucinations in Charles Bonnet Syndrome

Morgan, Katrine daSilva; Schumacher, Julia; Collerton, Daniel; Colloby, Sean J.; Elder, Greg J.; Olsen, Kirsty; Ffytche, Dominic; Taylor, J-P

doi:10.1016/j.ophtha.2022.06.041

Cited by 4 publications

(3 citation statements)

References 39 publications

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“…One explanation for these findings is the excitability of visual cortex. As previously mentioned, multiple sources of evidence suggest that excitability of early visual cortices may be responsible for or precede hallucinatory experiences 3,45,[58][59][60] . While more research in larger samples is needed to test this hypothesis, it is plausible that age-related changes in the excitability of the visual system could occur, contributing to the generation and propagation of hallucinatory experiences.…”

Section: Discussionmentioning

confidence: 92%

“…There is a multitude of evidence to suggest that low-level aberrant noise, excitability, or direct activation of early visual cortices, which may be interpreted as signal, may be responsible for hallucinatory experiences. Patients with Charles Bonnet syndrome present with a build-up of neural activity in early visual cortex prior to the onset of a hallucination 58 , and respond well to inhibitory stimulation of the visual cortices 59 . Psychedelic drugs such as LSD and psilocybin may bring about some of their low-level geometric visual effects from direct activation of 5HTA receptors, which are populous in early visual cortex, causing excitation 16 .…”

Section: Discussionmentioning

confidence: 99%

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Flicker and Ganzfeld induced visual hallucinations differ in frequency and content

Shenyan

Lisi

Greenwood

et al. 2023

Preprint

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Hallucinatory experiences, defined as perception in the absence of external stimuli, can occur in both pathological and non-pathological states and can be broadly phenomenologically divided into those of a simple and a complex nature. Non-pathological visual hallucinations can be induced experimentally using a variety of stimulation conditions. To assess whether these techniques drive a shared underlying hallucinatory mechanism, despite these differences, we compared two methods: flicker and perceptual deprivation (Ganzfeld). Specifically, we measured the frequency and complexity of the hallucinations produced by these techniques. We utilised button press, retrospective drawing, interviews, and questionnaires to quantify hallucinatory experience in 20 participants. With both experimental techniques, we found that simple hallucinations were more common than complex hallucinations. We also found that on average, flicker was more effective than Ganzfeld at eliciting a higher number of hallucinations, though Ganzfeld hallucinations were longer than flicker hallucinations. There was no interaction between experimental condition and hallucination complexity, suggesting that the increased bottom-up visual input in flicker increased both simple and complex hallucinations similarly. A correlation was observed between the total proportional time spent hallucinating in flicker and Ganzfeld, which was replicated in a retrospective questionnaire measure of experienced intensity, suggesting a shared hallucinatory mechanism between the two methodologies. We attribute these findings to a shared low-level core hallucinatory mechanism, such as excitability of visual cortex, which is amplified in flicker compared to Ganzfeld due to heightened bottom-up input.

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Section: Discussionmentioning

confidence: 92%

Section: Discussionmentioning

confidence: 99%

Flicker and Ganzfeld induced visual hallucinations differ in frequency and content

Shenyan

Lisi

Greenwood

et al. 2023

Preprint

View full text Add to dashboard Cite

show abstract

“…There is a multitude of evidence to suggest that low-level aberrant noise, excitability, or direct activation of early visual cortices, which may be interpreted as signal, may be responsible for hallucinatory experiences. Patients with Charles Bonnet syndrome present with a build-up of neural activity in early visual cortex prior to the onset of a hallucination 59 , and respond well to inhibitory stimulation of the visual cortices 60 . Psychedelic drugs such as LSD and psilocybin may bring about some of their low-level geometric visual effects from direct activation of 5HTA receptors, which are populous in early visual cortex, causing excitation 22 .…”

Section: Discussionmentioning

confidence: 99%

Visual hallucinations induced by Ganzflicker and Ganzfeld differ in frequency, complexity, and content

Shenyan,

Lisi,

Greenwood

et al. 2024

Sci Rep

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Visual hallucinations can be phenomenologically divided into those of a simple or complex nature. Both simple and complex hallucinations can occur in pathological and non-pathological states, and can also be induced experimentally by visual stimulation or deprivation—for example using a high-frequency, eyes-open flicker (Ganzflicker) and perceptual deprivation (Ganzfeld). Here we leverage the differences in visual stimulation that these two techniques involve to investigate the role of bottom-up and top-down processes in shifting the complexity of visual hallucinations, and to assess whether these techniques involve a shared underlying hallucinatory mechanism despite their differences. For each technique, we measured the frequency and complexity of the hallucinations produced, utilising button presses, retrospective drawing, interviews, and questionnaires. For both experimental techniques, simple hallucinations were more common than complex hallucinations. Crucially, we found that Ganzflicker was more effective than Ganzfeld at eliciting simple hallucinations, while complex hallucinations remained equivalent across the two conditions. As a result, the likelihood that an experienced hallucination was complex was higher during Ganzfeld. Despite these differences, we found a correlation between the frequency and total time spent hallucinating in Ganzflicker and Ganzfeld conditions, suggesting some shared mechanisms between the two methodologies. We attribute the tendency to experience frequent simple hallucinations in both conditions to a shared low-level core hallucinatory mechanism, such as excitability of visual cortex, potentially amplified in Ganzflicker compared to Ganzfeld due to heightened bottom-up input. The tendency to experience complex hallucinations, in contrast, may be related to top-down processes less affected by visual stimulation.

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Lesion network guided neuromodulation to the extrastriate visual cortex in Charles Bonnet syndrome reduces visual hallucinations: A case study

Raymond,

Trotti,

Oss

et al. 2024

Cortex

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Transcranial Direct Current Stimulation in the Treatment of Visual Hallucinations in Charles Bonnet Syndrome

Cited by 4 publications

References 39 publications

Flicker and Ganzfeld induced visual hallucinations differ in frequency and content

Flicker and Ganzfeld induced visual hallucinations differ in frequency and content

Visual hallucinations induced by Ganzflicker and Ganzfeld differ in frequency, complexity, and content

Lesion network guided neuromodulation to the extrastriate visual cortex in Charles Bonnet syndrome reduces visual hallucinations: A case study

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