Quantitative and temporal relationship between local cerebral blood flow and neuronal activation induced by somatosensory stimulation in rats.

In many studies on functional neuroimaging, change in local cerebral blood flow induced by sensory stimulation (evoked LCBF) is used as a marker for change in cortical neuronal activity, although a full description of the relationship between the evoked LCBF and neuronal activity has not been given. The purpose of this study was to estimate the close relationship between the evoked LCBF and neuronal activity. We measured the field potential using an electrode inserted into the cortex and the evoked LCBF using Laser-Doppler flowmetry in alpha-chloralose-anesthetized rats during somatosensory stimulation. Activation of the cortex was carried out by electrical stimulation of the hind paw with 1.5 mA pulses (0.1 ms) applied at the frequencies of 0.2,1,5 and 10 Hz for a 5 s duration, and at the frequencies of 1 and 5 Hz for 2,5 and 15 s durations. The response magnitude of the evoked LCBF reached the maximum at 5 Hz. During the 5 s stimulation, the pattern of change in the response magnitude of evoked LCBF to various frequencies reflected the integrated amplitude of field potentials. During the 15 s stimulation, the evoked LCBF at 5 Hz exhibited an initial peak followed by a plateau phase, although there was no initial peak at 1 Hz. These changes in evoked LCBF during the 15 s stimulation reflected change in field potentials, but they were delayed during the temporal change in field potentials. These results suggest that the response of evoked LCBF reflects the integrated neuronal activity during the stimulation period, and it is modulated by a temporal slow function.