Hippocampal injury causes various neurological and psychiatric problems including a memory impairment disorder--transient global amnesia (TGA) ^1,2. Recent MRI studies on TGA patients reported 1 to 5 mm punctuate high-signal intensity lesions in the hippocampal CA1 region^3,4. Despite the extensive brain mapping studies on patients or animals⁵, the mechanisms of this region-specific vulnerability of hippocampal CA1 vasculature are still poorly understood. Previously, we have developed a single-vessel fMRI method to visualize the hemodynamic response from individual vessels in the deep layer cortex⁶. In this work, we combined single-vessel fMRI with optogenetics to map the light-driven hemodynamic responses from individual venules in the hippocampus⁷. This work allows us to further study the neuronal and vascular interaction underlying the focal hippocampus stoke of a rat model, which may mimic the pathophysiological basis of TGA.fMRI were performed in alpha-chloralose anesthetized rats. The detailed surgical procedures were described previously⁸. Briefly, all images were acquired with a 14.1T/26cm horizontal bore magnet (Magnex), interfaced to an AVANCE III console (Bruker) and equipped with a 12 cm gradient set, capable of providing 100 G/cm with a rise time of 150us (Resonance Research). A transmit/receive surface coil with 10 mm diameter was used to acquire fMRI images. For fMRI, a 3D EPI sequence with a 64x64x16 matrix was run with the following parameters: TE 14ms; TR 93.75ms; FOV 1.92x1.92x0.8cm³; spatial resolution 300x300x500μm³. To detect individual arterioles and venules, a 2D-MGE sequence was used with the following parameters: TR 50ms; TE 2.5, 5.5, 11.5, 14.5, 17.5, 17.5, 20.5, 23.5ms; flip angle 58°; matrix 256x192; in-plane resolution 67x67μm; 400 um thickness for 14T. Line-scanning fMRI: A 2D FLASH sequence was applied to map the fMRI signal with the following parameters: TE 12.5ms (BOLD); TR 100ms; matric 172x128 (BOLD); flip angle 30°; slice thickness 500μm for 14T. The 2D FLASH slice images were reconstructed from the reshuffled k space data with 100ms sampling rate. ChR2 was expressed by AAV5 viral vectors in the hippocampal CA1 region with CaMKII promoter. Fiber optic (200μm) was inserted into the hippocampus for optical stimulation, the light pulse was delivered through the 473nm laser (10Hz, 2s duration, pulse length, 20ms, 2.5mw, 8 epoch). AFNI software was used for image analysis.Fig. 1A shows the fiber optic insertion into the hippocampus, where the ChR2 was expressed by AAV viral vector. The fiber optic trace was also visible in the brain slice for immunostaining. The light-driven fMRI signal was detected in the hippocampus close to the fiber tip, where the voxel-wise time course from the activated hippocampal regions were shown in Fig. 1B. Fig. 2 shows the arteries and venules map (A-V map) with arterioles in bright spots and venules in dark spots. The peak BOLD voxels were primarily overlapped with the venule voxels (blue arrows) on the hippocampus.We reported the light-driven single-vessel fMRI in the hippocampal regions of the rat brain for the first time. The vessel specific fMRI signal allows us to further examine the underlying neuronal and vascular coupling events in a focal hippocampal stroke rat model to mimic the transient global amnesia.