Interhemispheric integration at different spatial scales: the evidence from EEG coherence and FMRI

Area of Science:

• Neuroscience
• Visual Perception
• Cognitive Science

Background:

• The early visual system processes spatial frequencies (SFs) independently.
• Understanding the neural basis of integrating scale-specific visual information across hemispheres is crucial.

Purpose of the Study:

• To map brain regions and neural assemblies involved in interhemispheric integration of spatial frequency information.
• To investigate the role of Gestalt grouping rules in this integration process.

Main Methods:

• Simultaneous electroencephalography (EEG) coherence and functional magnetic resonance imaging (fMRI) BOLD signal measurements.
• Subjects viewed bilateral gratings with varying SFs that either obeyed (iso-oriented, IG) or violated (orthogonally oriented, OG) Gestalt grouping rules.
• Analysis of EEG beta frequencies (beta1, beta2) and corresponding BOLD activations in ventral and dorsal brain regions.

Main Results:

• Iso-oriented (IG) stimuli synchronized EEG at beta frequencies and increased BOLD signals in ventral and dorsal regions compared to orthogonally oriented (OG) stimuli.
• Beta1 EEG coherence correlated with ventral brain activations, while beta2 coherence correlated with dorsal activations.
• Both ventral and dorsal networks showed SF-dependent modulation of interhemispheric integration.

Conclusions:

• Distributed neural substrates in ventral and dorsal brain regions mediate interhemispheric integration of visual information at specific spatial frequencies.
• The integration process is influenced by Gestalt grouping principles.
• Spatial frequency content modulates the relative contribution of ventral and dorsal neural networks.