Repetitive correlated spiking can induce long-term potentiation (LTP) and long-term depression (LTD) of many excitatory synapses on glutamatergic neurons,in a manner that depends on the timing of pre-and postsynaptic spiking.However,it is largely unknown whether and how such spike timing-dependent plasticity (STDP) operates at neocortical excitatory synapses on inhibitory interneurons,which have diverse physiological and morphological characteristics.In this study we found that these synapses exhibit target cell-dependent STDP.In layer 2/3 of the somatosensory cortex,the pyramical cell (PC) forms divergent synapses on fast spiking (FS) and low-threshold spiking (LTS) interneurons that exhibit short-term synaptic depression and facilitation in response to high-frequency stimulation,respectively.At PC-LTS synapses,repetitive correlated spiking induced LTP or LTD,depending on the timing of pre-and postsynaptic spiking.