Figure 6: STDP modulation by gliotransmitter regulation of synaptic release. ((a), (b)) Rationale of LTD and LTP without ((a1), (b1)) and with either release-decreasing ((a2), (b2), ) or release-increasing gliotransmission ((a3), (b3), ) setting on at the red/green marks. (c) Percentage of time spent by postsynaptic transients (left panel) above depression (dashed lines) and potentiation thresholds (solid lines) for spike-timing intervals () within 100 ms and resulting STDP curves (right panel) in the absence of gliotransmission (no gliot., black curve) and with maximal release-decreasing (RD, red curve) or release-increasing gliotransmission (RI, green circles). (d) In general, strength and direction (i.e., “type”) of gliotransmission may dramatically modulate STDP. For example, synaptic changes are attenuated when synaptic release is decreased by gliotransmission (area below the black dashed line). Conversely, for sufficiently strong release-increasing gliotransmission (area above the black dotted line), the LTP window shrinks and LTD may be measured for all , as well as for sufficiently large . (e) A closer inspection of STDP curves indeed reveals that LTD (yellow curve) increases for larger synaptic release accounted by gliotransmission, while the ratio between areas underneath the LTP and LTD (magenta curve), initially in favor of the former (i.e., for release-decreasing gliotransmission), reduces to zero for large enough release-increasing gliotransmission, when two open LTD windows appear outside a small LTP window center for small (hatched area). Synaptic parameters:  s,  s, and  s. Other parameters as in Table 1 except for , ms, ,  s in ((a), (b)), and  s otherwise.