I’ve long been fascinated with synesthesia, a condition in which”the real information of one sense is accompanied by a perception of another sense.” Humans have reported the ability to perceive sounds as having certain colors (sometimes even the ability to “see” music) or “taste” certain words. More commonly, synesthetes perceive numbers and letters as having distinct colors.
While humans have been known to experience synesthesia by using hallucinogenic drugs or after brain injury, German scientists have been able to re-wire fruit fly larvae to perceive blue light as smelling like bananas. Although normal larvae would retreat from light, these larvae were thus attracted to it:
The work involves activating single receptor neurons out of 28 olfactory neurons. All the olfactory neurons were capable of producing a protein that is activated by light. The researchers had to choose which one to make light-sensitive.
They found they could either activate cells which would normally register repulsive odors and make the flies go away, or they could activate cells that respond to attractive odors like banana, marzipan or glue. Those odors are all present in rotting fruit, which attracts fruit flies.
The neurons send an electrical signal if they are stimulated with blue light, giving the fly larvae the impression that it has smelled something. As shown in the photo, the larvae went toward the light. The point is to study how the neural network operates, the researchers say.
There are certain instances where synesthesia could potentially be beneficial – this list of famous synesthetes seems to indicate it’s especially common (relatively speaking) among musicians.