Correlation- versus integration-analysis implications for functional magnetic resonance imaging and optical recording of intrinsic signals (ORIS)

Functional magnetic resonance imaging (fMRI), based on the blood oxygenation level dependent (BOLD) effect was combined with optical recording of intrinsic signals (ORIS) from the gerbil barrel cortex. The comparison of spatial and temporal aspects of the signals revealed that the hemodynamic basis of a positive fMRI BOLD signal is not inevitably a depletion of deoxyhemoglobin, as generally assumed, but could rather be caused by an increase in blood volume in the presence of persistently elevated deoxyhemoglobin levels during stimulation. Moreover, combining integrative and correlative analysis strategies for the two ORIS signals (deoxyhsmoglobin and total blood volume) it could be shown, that changes in blood volume that are tightly correlated with the stimulation are confined to sites of neuronal activation. This knowledge could help to improve the spatial resolution of fMRI