Monday, November 7, 2011


My most recent article titled Visual Hallucinations Clinical Occurrence and Use in Differential Diagnosis which can be found ( The article defines visual hallucinations as a visual sensory perception without external stimulation, or operationally, as a behavioral syndrome in which a patient claims to see something or behaves as if he or she sees something that an observer cannot see.  One common form of hallucinations are from optic nerve disease which can be characterized by bright light in conditions where bright light is absent such as low light scenarios and closed eyelids.  This is usually stimulated by horizontal movement of the eye.  For whatever reason, the optic nerve is enflamed which causes the hallucinations.  Narcolepsy has also been found to cause hallucinations in cases of hypnagogic (falling asleep) of which 15-50% of subjects report experiencing hallucinations often occurring during sleep paralysis in which REM is interrupted.  Hypnopompic (waking up) subjects did not have a set % of occurrences.  Toxic or metabolic disorders often manifest different hallucinations due to low or high levels of chemicals affecting activity of optical nerves. 

The article also touches on area 17 or the primary occipital striate cortex.  This area of the brain is more likely to produce more unformed hallucinations or hallucinations that are noticeable but not clear.  In addition, area 18 or the area of the brain known as the peristriate visual association area has been found to produce patterned hallucinations such as swirls or checkered boxes.  Higher areas of visual association (area 19) produce complex hallucinations such as people and animals or larger more detailed hallucinations.

I also found it very interesting that children are much more likely than adults to have hallucinations such as imaginary friends or play objects as well as the ability to recall previously seen images as hallucinations.  Finally if anyone knows a great spot for more information on how LSD effects the brain let me know!


  1. Bressloff and Cowan (and others) have done some very interesting research on the neural dynamics of geometric visual hallucinations, modeling the effects of psychedelics like LSD to help elucidate the structure and connectivity of the visual cortex.

    Here are some recent papers:
    Bressloff, P.C. et al., 2001. Geometric visual hallucinations, Euclidean symmetry and the functional architecture of striate cortex. Philosophical Transactions of the Royal Society of London. Series B: Biological Sciences, 356(1407), pp.299-330.

    Bressloff, P.C. et al., 2002. What Geometric Visual Hallucinations Tell Us about the Visual Cortex. Neural Computation, 14(3), pp.473-491.

    Billock, V.A. & Tsou, B.H., 2007. Neural interactions between flicker-induced self-organized visual hallucinations and physical stimuli. Proceedings of the National Academy of Sciences, 104(20), pp.8490-8495.

    Billock, V.A., Havig, P.R. & Tsou, B.H., 2001. Dynamic fractal (1/f) noise as a driving force for hallucinatory pattern formation. Journal of Vision, 1(3), p.439.

  2. From a term paper I wrote for a Biopsych class: "Psychedelics like LSD tend to depress the inhibitory effects of the serotenergic system of the dorsal raphe (Rogawski and Aghajanian, 1981), changing the gain threshold of sensory neurons elsewhere in the brain – in effect, increasing their excitability. This can throw the cortical system out of equilibrium, in an example of spontaneous symmetry breaking. When the structure, organization and connectivity of
    the visual cortex is taken into account, models of the perturbed system tend to form excitation patterns in standing waves, such as lattices, evenly spaced dots, and stripes in various orientations. When these patterns are mapped onto the visual field, the results look exactly like the form constants described by Klüver and others: spirals, tunnels, cobwebs and more."

    Also, Bressloff and Cowan wrote a Scholarpedia article about their work:

    And, for more background: