Some interesting articles on synesthesia

[Gradient]

Hope some people can benefit from these. Together, they find a pretty convincing neural substrate for color-synesthesia.
The first is a condensed review article that may help to put the other two into context. It also has some other pretty nifty research review articles on there too - on time perception, face perception, and visual attention. The second is an analysis of the structural polymorphism required for an individual to be synesthetic (the color version, without drugs). The third is another review article with a wider focus on recent research done on the subject - specifically regarding the roles of attention, automaticity (executing behaviors without focused thought), and awareness to the condition.

Of course, the condition doesn't translate directly to psychedelic-induced synesthesia. However, it wouldn't surprise me at all if the compounds induced a transient and reversible pharmacological approximation of the condition.