Klinische Neurophysiologie 2012; 43 - P040
DOI: 10.1055/s-0032-1301590

Increased Intrinsic Network Connectivity in Grapheme-Colour Synaesthesia

A Dovern 1, GR Fink 1, ACB Fromme 2, AM Wohlschläger 3, PH Weiss-Blankenhorn 2, V Riedl 3
  • 1Klinik für Neurologie, Uniklinik Köln, Köln
  • 2Kognitive Neurologie (INM-3) - Forschungszentrum Jülich GmbH, Jülich
  • 3Abteilung für Neuroradiologie, Technische Universität München, München

Introduction: It has been hypothesized that synaesthesia, a condition in which stimulation of one sensory modality leads to additional abnormal perceptions, is caused by an increased connectivity between relevant brain regions. Support for increased structural connectivity in grapheme-colour synaesthetes is provided by diffusion tensor imaging studies. However, an investigation (with functional magnetic resonance imaging, fMRI) of coherent neuronal activity, i.e. functional connectivity in synaesthesia, is lacking to date.

Methods: Twelve grapheme-colour synaesthetes and twelve control subjects (matched for age, gender, handedness, and IQ) were scanned with fMRI during a resting-state period of 10 minutes. Intrinsic connectivity networks (ICNs) were extracted from the resting-state fMRI data by applying independent component analysis. A multiple spatial regression analysis revealed seven synaesthesia-relevant ICNs. The functional network connectivity (FNC) was characterized by calculating pairwise zero-lag time course correlations between these seven ICNs.

Results: The FNC analysis of the seven synaesthesia relevant ICNs revealed five significant connections for the control group. In contrast, 15 significant connections between the seven ICNs were present in the synaesthetes. The direct group comparison revealed that two specific network connections were significantly stronger in the synaesthetes: the connections between the medial and lateral visual networks and the right fronto-parietal network. Moreover, intrinsic network connectivity correlated significantly with the consistency of synaesthetic experiences.

Conclusion: Supporting neurobiological models of synaesthesia which hypothesize increased connectivity in synaesthesia, the current study reveals, for the first time, increased global and specific (intrinsic) functional network connectivity in grapheme-colour synaesthetes, complementing earlier findings of increased structural connectivity.