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

Abstract

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.

Flicker and Ganzfeld induced visual hallucinations differ in frequency and content

“…In this process, wave patterns of excitation akin to those associated with geometric Klüver-like form constants, are thought to encourage neural entrainment; the synchronisation of the brain's endogenous neural oscillations (e.g., the alpha rhythm) to an endogenous external stimulus such as the flicker 18,50 13,34,44 . In line with this, several studies have shown that simple hallucinations are most frequent when flicker is presented at the alpha-wave frequency of approximately 10 Hz 18,51 (although hallucinations also occur at other frequencies 13,14 ). In the case of flicker-induced complex hallucinations, it has been suggested that basic hallucinatory forms may provide a building block for interpretive top-down influences 13 .…”