Submitted on June 30, 2005
Accepted on March 27, 2006
Interhemispheric integration at different spatial scales: The evidence from EEG coherence and fMRI
Maria G Knyazeva1*, Eleonora Fornari2, Reto A Meuli2, and Philippe P Maeder2
1 Department of Radiology, Centre Hospitalier Universitaire Vaudois (CHUV), Lausanne, Switzerland; Department of Neurology, Centre Hospitalier Universitaire Vaudois (CHUV), Lausanne, Switzerland
2 Department of Radiology, Centre Hospitalier Universitaire Vaudois (CHUV), Lausanne, Switzerland
* To whom correspondence should be addressed. E-mail: maria.knyazeva{at}chuv.ch.
The early visual system processes different spatial frequencies (SF) separately. To examine where in the brain the scale-specific information is integrated, we mapped the neural assemblies engaged in interhemispheric coupling with EEG coherence and BOLD. During similar EEG and fMRI experiments, our subjects viewed centrally presented bilateral gratings of different SF (0.25-8.0 cpd), which either obeyed Gestalt grouping rules (iso-oriented, IG) or violated them (orthogonally-oriented, OG). The IG stimuli (0.5-4.0 cpd) synchronized EEG at discrete beta frequencies (beta1, beta2) and increased BOLD (0.5 and 2.0 cpd tested) in ventral (around collateral sulcus) and dorsal (parieto-occipital fissure) regions compared to OG. At both SF, the beta1 coherence correlated with the ventral activations, whereas the beta2 coherence correlated with the dorsal ones. Thus, distributed neural substrates mediated interhemispheric integration at single SF. The relative impact of the ventral vs. dorsal networks was modulated by the SF of the stimulus.
