This week’s Nature has a fascinating article where gene therapy was used to reverse colour blindness in monkeys. The remarkable thing is that the monkeys were red-green colour blind from birth because they lacked a long wavelength (L-opsin) gene. A virus containing the human L-opsin gene was injected into the monkey’s eyes. The virus inserted the gene into some of the medium wavelength cones. It took about 20 weeks for the inserted gene to be expressed robustly. The amazing thing is that almost immediately after robust expression the treated monkeys were able to discern the frequencies that were missing before in behavioural tests. In essence, they could now see the colour red when they couldn’t before.
The rapidity in which the behavioural effect occured implies that the neural plasticity required to adopt a new colour was minor. It could be possible that the neural mechanisms for the missing colours already exists since only the males of the species are colour blind (the females are not) and could thus be tapped into immediately. However, the gene was inserted randomly into the cones and developmentally it takes a few months before babies can distinguish colours so it is not obvious at all as to how the circuits could be idle for so long and suddenly be activated.
I think understanding how a new colour can suddenly pop into existence may be the avenue to investigate the neural basis of qualia. The researchers of the study are conducting human trials now on patients that have retinal degeneration. If it works, then it is only a matter of time before they try it on healthy humans with colour blindness. We can then ask them what they actually experience when they see red for the first time.