Simultaneous VEP and transcranial Doppler ultrasound recordings to investigate activation-flow coupling in humans

Simultaneous assessment of electrical as well as hemodynamic responses in visual stimulation tasks is a relatively new approach to investigate activation-flow coupling in humans. To investigate the relation of both signals, we compared visually evoked potentials (VEP) with evoked flow velocity responses in the posterior cerebral artery by performing different visual stimulation tasks in healthy students. Check sizes and flickering frequency of a checkerboard pattern and the radial visual field section of a dartboard pattern were varied. VEPs were expressed in amplitude differences. Hemodynamic changes were given in terms of a control system model specifying the gain, attenuation, natural frequency and rate time parameters. From the typical VEP amplitude differences, we found the early N75-P100 amplitude difference significantly correlated to the gain parameter of the hemodynamic response. Both parameters increased with higher complexity of the checkerboard pattern and increasing visual field sections, whereas they remained nearly stable in the chosen frequency range. To corroborate the hypothesis of a tight coupling, further studies have to prove if the strength of this coupling could be used in clinical conditions.