Cortical layer-dependent CBF changes induced by neural activity

Hemodynamic-based brain mapping techniques have been extensively used. However, spatial accuracy and extents of those techniques to neuronal active sites are poorly understood because most of the techniques are contaminated by signals from non-specific large blood vessels. To accurately determine the intrinsic cerebral blood flow (CBF) responses induced by neural activity, large vessel-free and tissue-specific CBF imaging techniques should be utilized. For this, the arterial spin labeling MRI technique with flow-crushing bipolar gradients was applied in the rat brain to examine contributions of large blood vessels to CBF MRI. It was found that the majority (80-90%) of signals of arterial spin labeled MRI originated from tissue and capillaries. The arterial spin labeling technique with minimal sensitivity to large vessels was used to determine whether signal changes induced by neural activity are laminar-specific. During somatosensory stimulation, the highest neural activities and metabolic responses were expected to be located at the middle layer (i.e., layer 4) in the rat somatosensory cortex. Functional foci in CBF fMRI were located at the middle of the somatosensory cortex, suggesting that the response of CBF MRI signals is specific to sites of neural activity.