Elektrophysiologische befunde bei der synasthesie

Synesthesia is a rare condition in which individuals who are stimulated in one modality simultaneously experience sensations in another (e.g. coloured hearing). A relation to eidetic abilities has been suggested. A group of 17 persons with colour-word synesthesia and a control group (n = 17) were tested in an experiment designed to induce a sensory conflict: In a study phase subjects were exposed multiple times to 4 Japanese characters, each of which having a specific colour. In the test phase, the subjects were again exposed to these characters. However, the colour-symbol combinations now varied randomly with the subjects' task to press one of four buttons having the same colour as the visualised symbol. Parallel to the testphase event-related potentials were recorded from 19 electrodes. The reaction times of both groups showed an interference between the colour learned during the study phase and the color presented in the test phase. No effect of learned colour was observed in the brain potentials. Hence the proposed relation of synesthesia to eidetic abilities could not be ascertained. However, a marked group difference was obtained, in that the waveforms of the synaesthetic subjects were more positive over anterior brain areas. This suggests that the frontal lobe plays a crucial role in the generation of the synaesthetic experience.