Supporting information for Shouval et al. (2002) Proc. Natl. Acad. Sci. USA, 10.1073/pnas.152343099

Supporting Figure 10

Fig. 10. Explanation of seemingly contradictory experimental results, by choice of different parameters. The experiment of Bi and Poo (1998) induced STDP at 1 Hz; at this frequency both LTP and LTD could be obtained. In contrast, in the experiments of Markram et al. (1997) no significant STDP occurred below 10 Hz. Obviously, the same parameters cannot be used to account for both experiments. We have accounted for Bi and Poo (1998) in the paper. Here, we show that the same model with different parameters can account for the results of Markram et al. (1997). Markram et. al. used neocortical slices, whereas Bi and Poo used hippocampal cultures. First, we assume that the NMDAR conductance is significantly smaller in these neocortical slices, so that GNMDA = –1/1350. This is reasonable because in the hippocampal culture, each neuron forms a small number of synapses, and each of these can have a large efficacy. Therefore, it seems reasonable to assume that in neocortical slices the synaptic efficacy of NMDARs will be smaller than in hippocampal cultures. In A and B, the temporal dynamics of calcium transients induced respectively by 5 and 10 Hz stimuli are shown. Because of the enhanced temporal integration, calcium levels at 10 Hz are higher than at 5 Hz. Therefore, thresholds for LTD and LTP (qd and qp, respectively) can be set so that at 5 Hz, no plasticity is induced regardless of Dt. At 10 Hz, baseline stimulation (black) induces no plasticity, Dt = –10 ms (red) results in LTD, and Dt = 10 ms (blue) results in LTP. The thresholds were set to qd = 0.35 mM as above, and qp = 0.45 mM. (C) The complete STDP curves induced at different frequencies. At 5 Hz (black) no significant plasticity occurs, at 10 Hz (blue) plasticity is induced such that at Dt = 10 ms, LTP is induced, and Dt = –10 ms LTD is induced. These results are consistent with the results of Markram et al. (1997). A further consequence is that at higher frequencies (green), only LTP is produced for all values of Dt, as in Fig. 5b. In addition, we show that at 7 Hz (red), there is a range of positive Dt at which LTD is induced. (D) Pairing-induced plasticity for the same parameters.