^I’m curious, have you ever sought treatment for the symptoms you describe?
As you seem to be aware, there is preliminary evidence that some antiepileptics (particularly Levetiracetam/Keppra) are effective in alleviating the persistent distortions in visual perception cause by psychedelics, as documented by the complete disappearance of EEG abnormalities in affected subjects. I have less confidence that antiepileptics are efficacious in treating the depersonalization/derealization aspects of HPPD, but there is enough evidence supporting the resolution of visual symptoms for me to recommend a medication trial for anyone that is significantly bothered by the phenomena. I would like to hear some anecdotal evidence regarding the efficacy (or lack thereof) of Levetiracetam for HPPD.
I have two hypotheses for the lasting visual phenomenon. First of all, induction of neurotrophic factors could potentially cause aberrant neuronal connections, which could reinforce the perceptual distortions experienced under the influence of a psychedelic. Under this premise, there would be unregulated proliferation in select regions of the visual cortex, resulting in durable synaptic changes. Large-scale proliferation of inhibitory connections in Layer 4 of V1 could cause problems with visual input. I think this hypothesis is less likely due to lack of evidence for the proposed mechanism.
I've also seen it proposed that symptoms could be due to increased 5-HT sensitivity of these inhibitory neurons in the claustrum and Layer 4 of V1. The lasting effect is difficult to explain, but a recent publication may shed some light on enduring alterations in neuronal function. In this hypothesis, histone acetylation and chromatin remodeling would be responsible long lasting changes in gene transcription. This hypothesis has been proposed to underlie cocaine-induced transcriptional changes in the nucleus accumbens, which are thought to be responsible for lasting changes in reward processing seen in addiction. For this hypothesis, there is emerging evidence for specific mechanisms.
Excellent paper from the May issue of Neuron.
http://www.ncbi.nlm.nih.gov.libproxy.lib.unc.edu/sites/entrez
And to ShaolinBomber, here is an excellent overview of visual processing and a potential mechanism for acute and chronic visual changes associated with psychedelic use.
Hypothesis of the mechanisms underlying visual distortions caused by psychedelic drugs