Is the magnitude of CBF and BOLD signals determined by the afferent input function?
To address this question we focused on recordings that would help us to monitor processing at the level of the excitatory synapse. The most commonly used indicator of synaptic function in vivo is the LFP, which is produced by synchronized activity of ensembles of nerve cells. Synaptic activity is associated with ion fluxes across the cell membrane that produce changes in the field potential. In an excitatory synapse, a net influx of positive ions is most commonly observed at the site of excitation. A net efflux of positive ions accompanies this from other parts of the same cell, leading to extracellular current flow. Because of the resistive properties of the extracellular media, this causes a potential change that can be measured as the extracellular or local field potential (Nicholson, 1973). In the following we use LFP amplitude measurements to indicate the magnitude of synaptic activity and relate this variable to CBF or BOLD signal amplitudes. The simultaneous recordings of electr
