Poster Sessions

Neu-22

Yoshiyuki Hirano

Y. Hirano, A. C. Silva

Spatio-temporal characteristics of the fMRI response to brief somatosensory stimulation in rats

The specificity of the hemodynamic response (HDR) to functional brain stimulation is determined on the spatial domain by the vascular architecture and on the temporal domain by the evolution of hemodynamic changes. In the present work, we set out to measure the BOLD, cerebral blood flow (CBF) and volume (CBV) HDR to brief somatosensory stimulation in alpha-chloralose anesthetized rats. Stimuli consisted of bilateral forepaw electrical pulses (333 us, 2 mA, 3 Hz) applied in individual epochs containing 1 to 6 or 30 electrical pulses, repeated in randomized order 10 or 16 times. BOLD-, CBV-, and CBF-fMRI were obtained with a GRE-EPI sequence (TE/TR: 25/250 ms, nominal resolution: 200 x 200 x 2000 μm3) at 7T. The BOLD-, CBF- and CBV-HDR to a single pulse is robustly detectable. In addition, the CBV-HDR to brief stimuli is essentially identical to the corresponding CBF-HDR in having fast onset, time-to-peak and offset. However, the CBV-HDR to longer stimuli includes significant contributions from the venous vasculature, which slows its dynamics during the rise and fall of the response. Detailed study of both spatial and temporal aspects of the HDR to brief stimuli will allow for a better understanding of the mechanisms of neurovascular coupling.