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Open Access Highly Accessed Research article

Pre-attentive modulation of brain responses to tones in coloured-hearing synesthetes

Lutz Jäncke1234*, Lars Rogenmoser1, Martin Meyer24 and Stefan Elmer1*

Author Affiliations

1 Division Neuropsychology, Institute of Psychology, University of Zurich, Binzmühlestrasse 14/25, Zurich CH-8050, Switzerland

2 Center for Integrative Human Physiology, Zurich, Switzerland

3 International Normal Aging and Plasticity Imaging Center (INAPIC), Zurich, Switzerland

4 Research Unit “Plasticity and learning in the aging brain”, University of Zurich, Zurich, Switzerland

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BMC Neuroscience 2012, 13:151  doi:10.1186/1471-2202-13-151

Published: 14 December 2012

Abstract

Background

Coloured-hearing (CH) synesthesia is a perceptual phenomenon in which an acoustic stimulus (the inducer) initiates a concurrent colour perception (the concurrent). Individuals with CH synesthesia "see" colours when hearing tones, words, or music; this specific phenomenon suggesting a close relationship between auditory and visual representations. To date, it is still unknown whether the perception of colours is associated with a modulation of brain functions in the inducing brain area, namely in the auditory-related cortex and associated brain areas. In addition, there is an on-going debate as to whether attention to the inducer is necessarily required for eliciting a visual concurrent, or whether the latter can emerge in a pre-attentive fashion.

Results

By using the EEG technique in the context of a pre-attentive mismatch negativity (MMN) paradigm, we show that the binding of tones and colours in CH synesthetes is associated with increased MMN amplitudes in response to deviant tones supposed to induce novel concurrent colour perceptions. Most notably, the increased MMN amplitudes we revealed in the CH synesthetes were associated with stronger intracerebral current densities originating from the auditory cortex, parietal cortex, and ventral visual areas.

Conclusions

The automatic binding of tones and colours in CH synesthetes is accompanied by an early pre-attentive process recruiting the auditory cortex, inferior and superior parietal lobules, as well as ventral occipital areas.

Keywords:
Coloured-hearing synesthesia; Crossmodal integration; EEG; Mismatch negativity; Auditory cortex