Fig. 4

Short-term dynamics of neuronal output (PS) depends on stimulation frequency and intensity and highly differ between DH and VH. Diagrams in the two panels (upper, DH and lower, VH) show frequency-dependent short-term changes in PS induced by a ten-pulse train delivered at two stimulation intensities producing a PS of 0.5–1 mV (suprathreshold response; circles) and a PS 75% of its maximal value (submaximal response; diamonds) respectively. The bottom right diagrams in the two panels show the average value of PS changes produced by the 8th–10th stimuli (steady state response) plotted as a function of stimulation frequency. Horizontal bars mark the stimulation epoch in which significantly different responses were observed between suprathreshold and submaximal stimulation (MANOVA among all responses in a train and independent t-test of individual responses). Asterisks denote the level of significance: *p < 0.05, ***p < 0.005. Data presented in the two stimulation intensities (suprathreshold and submaximal) were obtained from (slices/rats): 11/6 and 9/4 in DH and 11/6, and 10/5 in VH. In the DH the intensity of 1–40 Hz stimulation strongly influenced steady-state changes of PS (independent t-test, bottom-right graph). On the contrary, only the second response in a train was significantly facilitated by 20–75 Hz suprathreshold stimulation in the VH (MANOVA and independent t-test). Stimulation intensity did not significantly influence steady-states of PS in the VH at any stimulation frequency (independent t-test, p > 0.05). Note that steady-states of PS changes greatly differ between DH and VH (see also Fig. 5)