Figure 4.

Electrophysiological responses and variations in blood oxygen level-dependent (BOLD) signal intensities during electrical stimulation of the perforant pathway with repetitive, and 2.5 Hz stimulation trains under isoflurane or medetomidine. (Top) Under isoflurane, BOLD responses in the dentate gyrus were only generated during 2.5 Hz stimulation trains. In contrast, in the striatum, significant BOLD signal responses were detected during all stimulation trains. Consequently, 3D visualization of activated voxels highlights only the striatum as an activated region. Recorded electrophysiological responses indicate that during 1.25 Hz stimulation, the population spike latency increased during each train. (Bottom) Under medetomidine, stimulus-induced variations in BOLD signal intensities observed during 1.25 Hz stimulation trains. 3D visualization of activated voxels depicts only a restricted region in the dentate gyrus. Concurrent electrophysiological recordings also indicate that during 1.25 Hz stimulation trains, a variation in the processing of successive stimuli took place. Thus, population spike latencies always increase after the first stimulus, as seen also during the 2.5-Hz stimulation trains; however, augmentation of the population spike amplitude was absent.