還記得朱自清《荷塘月色》中的“微風過處,，送來縷縷清香，仿佛遠處高樓上渺茫的歌聲似的”嗎,？這名句常被用來舉例說明“通感”這種不同感覺在大腦中互相溝通交錯的現象,。英國一項最新研究說,，這種現象并非文學家的比喻,，而有其生理基礎,。
牛津大學研究人員在新一期《當代生物學》雜志上報告了相關成果。據介紹,，通感現象有多種表現,，與朱自清“聽見”香味相似，有的人可以“看見”聲音,，即在聽到某些聲音時眼前會出現某種顏色,，還有些人在看到某些特別的數字或字母時眼前會浮現出某種顏色。本次研究的對象就是一些有最后這一種通感表現的人,。
研究中使用了一種磁刺激手段,，即對大腦特定部位施加微弱的磁場，觀察大腦皮層的反應,。結果顯示,，與普通人相比，那些有通感表現的受試者大腦中的視覺皮層更加敏感和活躍,，只需很小的刺激,，他們的視覺神經元就會發(fā)出相應信號。
研究人員德溫·特休恩說,，大腦中與視覺功能相關的皮層特別敏感可能是造成通感現象的原因,，相關受試者雖然只看到一些字母或數字，但其視覺皮層被激起了關于顏色的反應,。
本次研究還顯示,，這種通感能力的大小是可調節(jié)的。通過對大腦相應區(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得更高，受試者的通感表現就更為明顯,；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.
