還記得朱自清《荷塘月色》中的“微風(fēng)過(guò)處,，送來(lái)縷縷清香,，仿佛遠(yuǎn)處高樓上渺茫的歌聲似的”嗎？這名句常被用來(lái)舉例說(shuō)明“通感”這種不同感覺(jué)在大腦中互相溝通交錯(cuò)的現(xiàn)象,。英國(guó)一項(xiàng)最新研究說(shuō),，這種現(xiàn)象并非文學(xué)家的比喻，而有其生理基礎(chǔ),。
牛津大學(xué)研究人員在新一期《當(dāng)代生物學(xué)》雜志上報(bào)告了相關(guān)成果,。據(jù)介紹，通感現(xiàn)象有多種表現(xiàn),，與朱自清“聽(tīng)見(jiàn)”香味相似,，有的人可以“看見(jiàn)”聲音，即在聽(tīng)到某些聲音時(shí)眼前會(huì)出現(xiàn)某種顏色,，還有些人在看到某些特別的數(shù)字或字母時(shí)眼前會(huì)浮現(xiàn)出某種顏色,。本次研究的對(duì)象就是一些有最后這一種通感表現(xiàn)的人。
研究中使用了一種磁刺激手段,，即對(duì)大腦特定部位施加微弱的磁場(chǎng),，觀察大腦皮層的反應(yīng)。結(jié)果顯示,，與普通人相比,，那些有通感表現(xiàn)的受試者大腦中的視覺(jué)皮層更加敏感和活躍，只需很小的刺激,，他們的視覺(jué)神經(jīng)元就會(huì)發(fā)出相應(yīng)信號(hào),。
研究人員德溫·特休恩說(shuō)，大腦中與視覺(jué)功能相關(guān)的皮層特別敏感可能是造成通感現(xiàn)象的原因,，相關(guān)受試者雖然只看到一些字母或數(shù)字,，但其視覺(jué)皮層被激起了關(guān)于顏色的反應(yīng)。
本次研究還顯示,，這種通感能力的大小是可調(diào)節(jié)的。通過(guò)對(duì)大腦相應(yīng)區(qū)域施加特殊的電流,，可以改變這些區(qū)域中大腦皮層的敏感程度,。如果把大腦皮層敏感度調(diào)得更高，受試者的通感表現(xiàn)就更為明顯,；而如果降低大腦皮層的敏感度,，甚至可以完全消除通感現(xiàn)象,。（生物谷 Bioon.com）
doi:10.1016/j.cub.2011.10.032
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Enhanced Cortical Excitability in Grapheme-Color Synesthesia and Its Modulation
Devin Blair Terhune, Sarah Tai, Alan Cowey, Tudor Popescu, Roi Cohen Kadosh
Synesthesia is an unusual condition characterized by the over-binding of two or more features and the concomitant automatic and conscious experience of atypical, ancillary images or perceptions. Previous research suggests that synesthetes display enhanced modality-specific perceptual processing, but it remains unclear whether enhanced processing contributes to conscious awareness of color photisms. In three experiments, we investigated whether grapheme-color synesthesia is characterized by enhanced cortical excitability in primary visual cortex and the role played by this hyperexcitability in the expression of synesthesia. Using transcranial magnetic stimulation, we show that synesthetes display 3-fold lower phosphene thresholds than controls during stimulation of the primary visual cortex. We next used transcranial direct current stimulation to discriminate between two competing hypotheses of the role of hyperexcitability in the expression of synesthesia. We demonstrate that synesthesia can be selectively augmented with cathodal stimulation and attenuated with anodal stimulation of primary visual cortex. A control task revealed that the effect of the brain stimulation was specific to the experience of synesthesia. These results indicate that hyperexcitability acts as a source of noise in visual cortex that influences the availability of the neuronal signals underlying conscious awareness of synesthetic photisms.
