LSD alters eyes-closed functional connectivity within the early visual cortex in a retinotopic fashion

Under LSD, the visual cortex's resting-state functional connectivity (RSFC) becomes more dependent on its intrinsic retinotopic organization, as if the brain were processing actual visual input despite closed eyes. In 10 healthy subjects, RSFC between non-adjacent patches of V1 and V3 that represent congruent parts of the visual field (both horizontal or both vertical meridians) was significantly stronger than connectivity between incongruent patches (horizontal-vertical), compared to placebo. The difference between congruent and incongruent connectivity was greater under LSD (Cohen's d=1.6), suggesting that psychedelic imagery involves transient local retinotopic activation similar to that from visual stimulation.

Study at a glance

Abstract

ABSTRACT Introduction: The question of how spatially-organized activity in the visual cortex behaves during eyes-closed, LSD-induced, visual psychedelic imagery has never been empirically addressed, although it has been proposed that under psychedelics the brain may function "as if" there is visual input when there is none (de Araujo, et al., 2012). We suspected that eyes-closed psychedelic imagery might involve transient local retinotopic activation, of the sort typically associated with visual stimulation. To test this, it was hypothesised that under LSD areas of the visual cortex with congruent retinotopic representations would show stronger RSFC compared to areas with incongruent retinotopic representations. Method: In this work, resting-state functional connectivity (RSFC) data was collected from 10 healthy subjects under the influence of LSD and, separately, placebo. Using a retinotopic localiser performed during a non-drug baseline condition, non-adjacent patches of V1 and V3 that represent the vertical or the horizontal meridians of the visual field were identified. Subsequently, RSFC between V1 and V3 was measured with respect to these a priori identified patches for both LSD and placebo. Results: Consistent with our prior hypothesis, the difference between RSFC of patches with congruent retinotopic specificity (horizontal-horizontal and vertical-vertical) and those with incongruent specificity (horizontal-vertical and vertical-horizontal) was significantly greater under LSD than placebo (p=0.0017, 1-tail, Cohen's d=1.6). Conclusion: The result suggest that activity within the visual cortex under LSD becomes more dependent on its intrinsic retinotopic organization. This result indicates that under LSD, in the eyes-closed resting-state condition, the early visual system behaves as if it were seeing spatially localized visual inputs. Reference de Araujo, D.B., Ribeiro, S., Cecchi, G.A., Carvalho, F.M., Sanchez, T.A., Pinto, J.P., De Martinis, B.S., Crippa, J.A., Hallak, J.E., Santos, A.C. (2012) Seeing with the eyes shut: Neural basis of enhanced imagery following ayahuasca ingestion. Human brain mapping, 33:2550-2560. Meeting abstract presented at VSS 2016