Nevertheless, the chemistry and biology of hallucinations remains elusive. Just one of many paradoxes: the 5HT-2a receptor is universally believed to be key to the mechanism, yet its strongest and most specific agonists don't seem to yield hallucinations. Motivated by Kluver's classic gallery of drawings by subjects experiencing closed-eye hallucinations, the physicist Jack Cowan and co-workers proposed a model wherein the observed images correspond to fundamental excitations of the cortex mapped conformally from the visual receptive field, as a representation of SO(3). His model accounts for many but not all of Kluver's images; however, experimental confirmation in human remains out of reach. Currently, the most effective non-human test bed for this class of drug involves rodents tilting their heads in response to putative auditory hallucinations, which may not always be suitably informative.

This raises the question: what organisms aside from human report their detailed perceptions in a form we can readily understand? Conventional wisdom has it that chimps can't draw, but parrots and chameleons also come to mind. This link to a video depicting a common inhabitant of the coral reefs visible from my window suggests that the octopus has evolved to report to would-be predators its detailed perception of its local environment. Remarkably little is understood about how this is achieved, and behavioral considerations confound all observations; nevertheless, promising experiments are described. .

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