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EEG coherence in post-LSD visual hallucinations.

H D Abraham1, F H Duffy

  • 1Department of Psychiatry, Mt. Auburn Hospital, 330 Mt. Auburn St., Cambridge, MA 02138, USA. abraham861@aol.com

Psychiatry Research
|September 22, 2001
PubMed
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Hallucinogen persisting perception disorder (HPPD) involves chronic visual hallucinations. This study found reduced brainwave coherence in HPPD individuals when eyes are open, but increased occipital coherence when eyes are closed, potentially explaining hallucinations.

Area of Science:

  • Neuroscience
  • Psychiatry

Background:

  • Chronic visual hallucinations can occur after LSD use, a condition known as hallucinogen persisting perception disorder (HPPD).
  • Understanding the neurophysiological underpinnings of HPPD is crucial for developing effective interventions.

Purpose of the Study:

  • To investigate differences in electroencephalogram (EEG) spectral coherence between individuals with HPPD and healthy controls.
  • To explore the relationship between EEG coherence patterns and the persistent visual hallucinations experienced in HPPD.

Main Methods:

  • EEG spectral coherence was measured in 38 HPPD subjects and 33 control subjects.
  • Coherence, assessing spectral similarity over time, was analyzed to estimate cortical coupling in different brain regions.
  • Comparisons were made between eyes-open and eyes-closed states.

Related Experiment Videos

Main Results:

  • HPPD subjects exhibited widespread reduction in EEG coherence in the eyes-open state.
  • Upon eye closure, HPPD subjects showed increased coherence within the occipital region but reduced coherence to more distant brain areas.
  • This localized occipital coherence increase correlated with shortened visual evoked potential latency.

Conclusions:

  • HPPD may involve widespread cortical inhibition when eyes are open, transitioning to localized occipital disinhibition upon eye closure.
  • This occipital hypersynchrony and relative visual cortex isolation, particularly when eyes are closed, may facilitate hallucinatory experiences.
  • The findings suggest a potential neurophysiological mechanism for HPPD, drawing parallels with epileptic activity.