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Title: Functional imaging investigation of psychedelic visual imagery
Author: Roseman, Leor
ISNI:       0000 0004 8499 4670
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2019
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Psychedelics can induce eyes-closed imagery in which various visions can be experienced. These visions vary from simple geometrical patterns, to more complex imagery, to full immersion within "other realms". Past studies suggest that the visual cortex is involved in processing these visions, yet these studies were limited into investigation of activity. In this thesis, the aim was to expand on the involvement of the visual cortex by investigating processes that are beyond simple activation maps, such as functional connectivity and dynamics. In study 1, it was hypothesized that the visual cortex will show increased functional connectivity with many cortical and subcortical regions. This was investigated with 15 subjects that were scanned using fMRI under the influence of 75 µg of LSD or placebo. The results of this study showed increased resting state functional connectivity (RSFC) between the primary visual cortex and many cortical and subcortical regions. This result correlated with subjective ratings of psychedelic imagery and with occipital alpha power suppression measured with MEG, which is a reliable neural correlate of the intensity of the psychedelic state. It study 2, it was hypothesized that connectivity within the visual cortex would match its retinotopic architecture. Retinotopic mapping is the representation of the visual field (the world we observe) in the visual cortex - e.g. areas which are near to each other in the visual field will be near each other in the visual cortex. In this study, it was found that under LSD (same procedure as study 1), with eyes closed, connectivity patterns between different subregions of the visual cortex matched the retinotopic mapping of these regions, suggesting that the visual system behaves as if it is seeing spatially localized input, with eyes-closed under LSD. In study 3, it was hypothesized that during the onset phase of psychedelic imagery, the activation of subregions of the visual cortex will be from low level to high level areas, which is according to the subjective dynamics of the experience - i.e. from simple to complex. This was tested in 9 subjects that were scanned in the fMRI during the onset or "come-up" phase - i.e. 3 minutes post (1 min) infusion of 2mg psilocybin IV - which has a particularly fast onset. Results in this study revealed that during the onset phase the BOLD dynamics of regions within the ventral stream are organized by the hierarchy of regions. Overall, study 1 and 2 revealed that, with eyes closed, under LSD, communication patterns between visual cortex and the rest of the brain and within the visual cortex match the kind of processing known to occur during regular vision. This adds to a body of knowledge supporting the view that the visual cortex is particularly engaged under the influence of psychedelics, and by measuring patterns of connectivity, we were able to provide strong support for the view that abnormal activity in the visual cortex underlies psychedelic imagery.
Supervisor: Nutt, David ; Carhart-Harris, Robin ; Leech, Robert Sponsor: Imperial College London
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral