Flicker light stimulation induces thalamocortical hyperconnectivity with LGN and higher-order thalamic nuclei

The thalamus is primarily known as a relay for sensory information; however, it also critically contributes to higher-order cortical processing and coordination. Thalamocortical hyperconnectivity is associated with hallucinatory phenomena that occur in various psychopathologies (e.g., psychosis, migraine aura) and altered states of consciousness (ASC, e.g., induced by psychedelic drugs). However, the exact functional contribution of thalamocortical hyperconnectivity in forming hallucinatory experiences is unclear. Flicker light stimulation (FLS) can be used as an experimental tool to induce transient visual hallucinatory phenomena in healthy participants. Here, we use FLS in combination with fMRI to test how FLS modulates thalamocortical connectivity between specific thalamic nuclei and visual areas. We show that FLS induces thalamocortical hyperconnectivity between LGN, early visual areas and proximal upstream areas of ventral and dorsal visual streams (e.g., hV4, VO1, V3a). Further, an exploratory analysis indicates specific higher-order thalamic nuclei, such as anterior and mediodorsal nuclei, to be strongly affected by FLS. Here, the connectivity changes to upstream cortical visual areas directly reflect a frequency-dependent increase in experienced visual phenomena. Together these findings contribute to the identification of specific thalamocortical interactions in the emergence of visual hallucinations. HighlightsO_LIFlicker light stimulation (FLS) induces thalamocortical hyperconnectivity between the first-order thalamic LGN and early visual cortices, likely due to entrainment. C_LIO_LIThalamocortical connectivity between LGN and upstream visual areas, but not V1, is associated with the intensity of visual hallucinations. C_LIO_LIThalamocortical connectivity changes with higher-order thalamic nuclei, such as anterior and mediodorsal nuclei, show strongest modulation by flicker frequency, which corresponds to the intensity of visual hallucinations. C_LI