Dr. Kevin Mitchell, a neuroscientist at Smurfit Institute of Genetics, University of Dublin, posted at his excellent blog Wiring the Brain about a weird, interesting study* that points to a possible genetic explanation of synaesthesia** (e.g., hearing a word and experiencing the color red). The authors were studying pain mechanisms in fruit flies (turns out the mechanisms are similar to us mammals, whuddathunk?). Once they identified a particular gene they dubbed straightjacket*** which is "involved in modulating neurotransmission," they systematically deleted it in test flies and discovered that the test subjects**** no longer processed the pain stimuli, even though the pain stimuli was following the pathway. In Mitchell's words:
Somehow, deletion of CACNA2D3 alters connectivity within the thalamus or from thalamus to cortex in a way that precludes transmission of the signal to the pain matrix areas. This is where the story really gets interesting. While they did not observe responses of the pain matrix areas in response to painful stimuli, they did observe something very unexpected – responses of the visual and auditory areas of the cortex! What’s more, they observed similar responses to tactile stimuli administered to the whiskers. Whatever is going on clearly affects more than just the pain circuitry (emphasis added).
So, if I understand this, they turned off the ability to recognize pain, but when they administered painful stimuli (heat), the test subjects had visual, auditory, and tactile experiences. Imagine putting a flame to your hand and seeing purple. Pretty frikkin awesome. Dr. Mitchell's post does more justice to this complex study, I just thought it was awesome.
*Geez! Take a look at the author list of the publication. Do you have a place for 12th author on YOUR CV?
**FYI: Synaesthesia is NOT the same thing as sound symbolism, necessarily. True synaesthesia is a rare phenomenon that appears to have biophysical roots. Sound symbolism is mostly hippie-dippy bullshit exploited by marketing professionals to sell stuff.
***I have no clue why they called it this, but it's a hell of a lot more awesome than CACNA2D3.
****There were multiple studies referenced, some involving fruit flies, some involving mice, and it wasn't clear to me which evidence came from which studies, so I have chosen to use the cover term "test subjects."
Neely GG, Hess A, Costigan M, Keene AC, Goulas S, Langeslag M, Griffin RS, Belfer I, Dai F, Smith SB, Diatchenko L, Gupta V, Xia CP, Amann S, Kreitz S, Heindl-Erdmann C, Wolz S, Ly CV, Arora S, Sarangi R, Dan D, Novatchkova M, Rosenzweig M, Gibson DG, Truong D, Schramek D, Zoranovic T, Cronin SJ, Angjeli B, Brune K, Dietzl G, Maixner W, Meixner A, Thomas W, Pospisilik JA, Alenius M, Kress M, Subramaniam S, Garrity PA, Bellen HJ, Woolf CJ, & Penninger JM (2010). A Genome-wide Drosophila Screen for Heat Nociception Identifies α2δ3 as an Evolutionarily Conserved Pain Gene. Cell, 143 (4), 628-38 PMID: 21074052