Figure 4: The effect of bidirectional chemical synapse in controlling firing synchrony between layer 1 interneurons.

To test for firing synchrony in three interneuron groups (C-coupled, E-coupled and D-coupled), paired spike trains were elicited by suprathreshold current in the driver cell (red traces, 30–50 Hz) and by tonic suprathreshold depolarization in the follower cell (blue traces, ∼10 Hz), respectively. (a) Sample traces of paired spike trains from two neurons coupled by different patterns of connectivity in neocortical layer 1, the arrowheads indicate the synchronous spikes. (b) Normalized cross-correlogram (Z-score) for neuron pairs in (a). Bin size is 2 ms. Note that the cross-correlogram exhibited a peak ∼0 ms in all three groups. (c) Average Z-scores for different patterns of connectivity. Note that Z-scores of E- and D-coupled pairs were significantly higher than that of C-coupled pairs, and Z-scores of D-coupled pairs were slightly lower than that of E-coupled pairs. (d) Average JBSI values for different patterns of connectivity. C-coupled pairs=4, E-coupled pairs=6, D-coupled pairs=7, from 10 mice. *P<0.05, **P<0.01, two-tailed paired t-test. Error bars represent mean±s.e.m.