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EEG coherence in post LSD visual hallucinations.

EEG coherence in post LSD visual hallucinations.

  1. Mindless
    The study is based on EEG spectral coherence, that is, the similarity over time of EEG signals. 38 HPPD subjects and 33 controls were studied. 'Measures of local and medium distance EEG spectral coherence were calculated from all subjects'. Coherence 'may estimate cortical coupling'. In the eyes-open state in HPPD subjects, widespread reduction of coherence was noted. However, upon eye closure the occipital region showed some increase in regional coherence, but 'reduced coherence of the occipital region to more distant regions'.


    There is a widespread cortical inhibition in the eyes-open state, but localised and isolated disinhibition upon eye closure, a state know to facilitate hallucinatory experiences. In HPPD, Abraham and Duffy speculate that an EEG hypersynchrony resulting from increased regional coherence, coupled with 'relative isolation of the visual cortex' gives rise to illusions and hallucinations, especially on eye closure.