Do functional neuroimaging signals represent action potentials in principal target cells in the activated brain region?
Increases in CBF or BOLD responses recorded by functional neuroimaging have traditionally been perceived as representing increases in spike activity in the principal target cells of the active brain region. This concept is the basis for the construction of physiological connectivity maps among cortical and subcortical regions (Friston and Price, 2001) and for the idea of a close relationship between the number of action potentials in cortical neurons and the imaging signal based on existing knowledge of the functional organization of the cerebral cortex (Malonek and Grinvald, 1996; Tagamets and Horwitz, 1998; Duong et al., 2001). However, both theoretical arguments and experimental results suggest that this apparent correlation occurs only in specific circumstances as discussed in the following. Activation of the cerebral cortex leads to desynchronization of the EEG that is not necessarily accompanied by increases in the overall discharge rate of cortical neurons (Creutzfeldt, 1975). M
