Characterization of extracellular glutamate dynamics in the hippocampus. A, Representative heatmaps of iGluSnFR responses after afferent stimulation (100 Hz). Peak responses are shown in the x–y plane (image size, 2 × 2 mm), and the y–z (time) plots show the kinetics of the response at a defined x-coordinate adjacent to the site of stimulation (image represents 2 s). The gray shaded area within the images denotes the onset and duration of afferent stimulation. B, Mean (±SEM) iGluSnFR response profiles to 2, 5, 10, 50, or 100 pulses of afferent stimulation at 100 Hz. C, Mean responses (±SEM) from B that were normalized to the peak value at the end of the stimulation. D–E, Grouped data showing mean (±SEM) iGluSnFR response peak (D) and decay tau (E). RM ANOVA with Tukey's post hoc results are indicated by *p < 0.05 and ***p < 0.001. F–G, Decay and %ΔF/F correlation of the iGluSnFR responses with a short burst of activity (F) and longer trains of high-frequency stimulation (G).