What is the medical explanation for HPPD?
A high proportion of HPPD subjects got HPPD very early in their experimentation with LSD (or other hallucinogens). This supports the theory that some people have a genetic predisposition to HPPD. Genetic or not, HPPD is a measurable physical problem with the brain. Brain scans of HPPD subjects show that there are regions of significantly elevated activity. HPPD subjects also perform worse on a few visual tests (see here): • Reduced sensitivity (HPPD subjects perceive a strobing light as being a continuous light at much lower frequencies then control subjects). • Reduced ability to discriminate between colors. There is an excellent paper on LSD visual effects which includes a possible explanation for HPPD in the Rhodium archive. According to this paper, the visual system in the brain has six different layers which detect different types of visual stimulus (horizontal bars excite one layer, vertical bars excite a different layer, for example). These different layers work together to proc
