Temporal coupling between neuronal activity and blood flow in rat cerebellar cortex as indicated by field potential analysis

1. Laser-Doppler flowmetry and extracellular recordings of field potentials were used to examine the temporal coupling between neuronal activity and i ncreases in cerebellar blood flow (CeBF). 2. Climbing fibre-evoked increases in CeBF were dependent on stimulus durat ion, indicating that increases in CeBF reflected a time integral in neurona l activity. The simplest way to represent neuronal activity over time was t o obtain a running summation of evoked field potential amplitudes (run Sigm a FP). Run Sigma FP was calculated for each stimulus protocol and compared with the time course of the CeBF responses to demonstrate coupling between nerve cell activity and CeBF. 3. In the climbing fibre system, the amplitude and time course of CeBF were in agreement with the calculated postsynaptic run Sigma FP (2-20 Hz for 60 s). This suggested coupling between CeBF and neuronal activity in this exc itatory, monosynaptic, afferent-input system under these conditions. There was no correlation between run Sigma FP and CeBF during prolonged stimulati on. 4. Parallel fibre-evoked increases in CeBF correlated with run Sigma FP of pre- and postsynaptic potentials (2-15 Hz for 60 s). At higher stimulation frequencies and during longer-lasting stimulation the time course and ampli tudes of CeBF responses correlated with run Sigma FP of presynaptic, but no t postsynaptic potentials. This suggested a more complex relationship in th is mixed inhibitory-excitatory, disynaptic, afferent-input system. 5. This study has demonstrated temporal coupling between neuronal activity and CeBF in the monosynaptic, excitatory climbing-fibre system. In the mixe d mono- and disynaptic parallel fibre system, temporal coupling was most cl early observed at low stimulation frequencies. We propose that appropriate modelling of electrophysiological data is needed to document functional cou pling of neuronal activity and blood flow.