There are people who hear color—and they may have hyper-connected brains

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For some, musical notes conjure flashes of color, letters and numbers have their own particular hues, and certain sounds tickle. Researchers have reported these extraordinary cases of sensory mixing, called synesthesia-loosely translated to perceived together-for more than 130 years. But the molecular underpinnings of the vibrant experiences have been a complete mystery-until now.

With the help of three large families of synesthetes, researchers identified a smattering of genes that may help explain their mingled senses. Several of the genes were involved in making connections among neurons within and across various brain regions. And additional data suggested that these genes are active in regions of the brain involved in receiving and processing visual and auditory information while those regions develop.

The findings, published this week in PNAS, appear to support the hypothesis that synesthesia is caused by hyper-connectivity among brain regions that handle our senses. Essentially, the idea is that dense, trippy sensory networks load up with signals that may spill over to each other or that extra connections bridge the different sensory systems, breaking down their "modularity."

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