Figure 5: Synchronous synaptic activity between layer 1 interneurons.

(a) Sample traces of spontaneous activity of four layer 1 interneurons. High-temporal-resolution displays of a segment of recordings (thick black line) are shown at the bottom. Green asterisks and dotted lines indicate synchronized events between two neurons (cell 1 and 3, red traces). (b) Normalized cross-correlogram (Z-score) for neuron pairs in a. Bin size is 1 ms. Note that the frequency of events is significantly increased at ∼0 ms (inset) for the interneuron pair (1 versus 3, red), but not for any other neuron pairs. The grey region in the inset corresponds to −1 ms≤Δt≤1 ms. Similar symbols and displays are used in subsequent figures. (c) Proportion of layer 1 interneuron pairs exhibiting synchronized spontaneous activity at different developmental stages. Note that synchronous synaptic activity appeared to be correlated with the developmental process. (d) Proportion of layer 1 interneuron pairs of different subtypes from P6 to P20 exhibiting synchronized spontaneous activity. (e) Proportion of electrically coupled or not coupled interneuron pairs from P6 to P20 exhibiting synchronized spontaneous activity. n=47 mice. *P<0.05, ***P<0.001, χ²-test and Fisher’s exact test.