Maria Angela Franceschini

Layer-specific interhemispheric functional connectivity in the somatosensory cortex of rats: resting state electrophysiology and fMRI studies.

The spontaneous cerebral hemodynamic fluctuations observed during the resting state have been frequently visualized using functional magnetic resonance imaging (rsfMRI). However, the neuronal populations and neuroelectric characteristics underlying the functional connectivity of cerebrohemodynamic activities are poorly understood. We investigated the characteristics of bi-hemispheric functional connectivity via electrophysiology and rsfMRI in the primary sensory cortex of rats anesthetized by α-chloralose. Unlike the evoked responses, the spontaneous electrophysiological activity was concentrated in the infragranular layers and could be classified into subtypes with distinctive current sources and sinks. Both neuroelectric and rsfMRI signals were interhemispherically correlated in a layer-specific manner, suggesting that there are independent neural inputs to infragranular and granular/supragranular layers. The majority of spontaneous electrophysiological activities were bilaterally paired with delays of up to ~50xa0ms between each pair. The variable interhemispheric delay implies the involvement of indirect, multi-neural pathways. Our findings demonstrated the diverse activity patterns of layer-specific electrophysiological substrates and suggest the recruitment of multiple, non-specific brain regions in construction of interhemispheric functional connectivity.

A spatial-temporal comparison of fMRI and NIRS hemodynamic responses to motor stimuli in adult humans

Near infrared spectroscopy (NIRS) has the ability to record, at high temporal resolution, hemodynamic changes within the brain during functional activity. Although alone, NIRS has a poorer spatial resolution compared to other imaging methods such as functional MRI (fMRI), multi-modality approaches, which attempt to fuse the spatial resolution of MRI with the hemoglobin oxygenation information and temporal resolution of NIRS, show promise to yielding better insight into the hemodynamic and metabolic response of the functional brain in future research. However, paramount to the development of these multi-modality approaches, proper control experiments to validate the correlation between NIRS and fMRI methods must be preformed. In this experiment, we have examined the spatial and temporal relationship between the NIRS measure of deoxy-hemoglobin and the fMRI blood oxygen level dependent (BOLD) signal. Here, we have modeled the propagation of light through realistic, tissue segmented, head models for each of five subjects. Using these sensitivity profiles, we predicted the measurement of deoxy-hemoglobin for each individual NIRS source-detector pair from the projection of the volume-wise fMRI BOLD changes, thus allowing a quantitative spatial and temporal comparison between NIRS and fMRI. We report a linear correlation of R = 0.73 (p < 2x10 -8) between the spatial profiles between the NIRS measure of deoxy-hemoglobin and BOLD signal. We also report a temporal correlation of R=0.88 (p<9x10 -18) between the region-of-interest averaged responses using the projected BOLD response.