Using 7T fMRI and MEG to examine functional properties of the human auditory pathways

Animal studies have demonstrated that intracortical laminar patterns can provide information about the type of inputs into a brain region. Feedforward (FF) input typically first arrives to the middle cortical layer, whereas feedback (FB) arrives to superficial and deep layers. However, it has been difficult to non-invasively test whether these principles apply to humans. We investigated the spatiotemporal characteristics of FF and FB inputs using ultra-high resolution 7-tesla functional MRI (fMRI), magnetoencephalography (MEG), and computational modeling. We studied the responses to simple auditory and visual stimuli (noise bursts and checkerboard). The fMRI results suggest that intracortical BOLD depth profiles could help distinguish between FF and FB influences in the human brain. The combined MEG and computational modeling results support the hypothesis that cross-sensory visual input in the auditory cortex is of FB type, whereas sensory-specific auditory input includes an initial FF input followed by an FB. Taken together, these studies illustrate how the patterns of the estimated layer-specific activity have potential to characterize inputs into cortical areas in terms of hierarchical organization.

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