During somatosensory stimulation, cerebral blood flow is coupled to integrated neuronal activity but not to averaged evoked potentials.

Ngai, A.C., M.A. Jolley, R. D’Ambrosio, J.R. Meno, and H.R. Winn. Frequency-dependent changes in cerebral blood flow and evoked potentials during somatosensory stimulation in the rat. Brain Research 837: 221-228, 1999.

Simultaneous recordings of somatosensory evoked potentials (SEPs) and laser-Doppler flow (LDF) from the rat cortex, during stimulation of the sciatic nerve (SNS). Stimulus duration was kept constant at 20s. Note that SEPs declined with increasing stimulus frequency, whereas LDF responses first increased from 1-5 Hz, and declined from 5-20 Hz. However, we reason that CBF should reflect integrated neuronal activity, and computed the sum of SEPS (SSEP = SEP ¥ stimulus frequency) as an index of total neuronal activity at each frequency (data not shown here). SSEP indeed correlates with LDF responses. Thus, during somatosensory stimulation at various frequencies, cerebral blood flow is coupled to integrated neuronal activity but not to averaged evoked potentials.