Research Article Induced Cross-Modal Synaesthetic Experience Without Abnormal Neuronal Connections

ABSTRACT—Are the kinds of abnormal cross-modal inter-actions seen in synaesthesia or following brain damage due to hyperconnectivity between or within brain areas, or are they a result of lack of inhibition? This question is highly contested. Here we show that posthypnotic suggestion in-duces abnormal cross-modal experience similar to that observed in congenital grapheme-color synaesthesia. Given the short time frame of the experiment, it is unlikely that new cortical connections were established, so we conclude that synaesthesia can result from disinhibition between brain areas. People see with their eyes, hear with their ears, and feel with their fingers, and they may also be aware of interactions between their senses; when people watch a movie, for example, the speakers give the illusion of sound coming from the people and events on the screen. In a small population of people, however, sensations triggered by one modality elicit either another ex-perience in the same modality or a perception experienced in a different modality. Such abnormal cross-modal interactions can occur following brain damage (Kupers et al., 2006; Pascual