Figure 6.

Paired-pulse facilitation in a L4-to-L2/3 IN connection. A, Train of three presynaptic APs at 10 Hz (top trace) and 20 consecutive sweeps that were on average facilitating in amplitude (bottom trace). B, Corresponding EPSP amplitude histograms for the first, second, and third EPSP in a train. Note the marked decrease in failure counts for the third EPSP compared with the first EPSP. The postsynaptic L2/3 interneuron of this connection had similarities to a bitufted or bipolar neuron with two primary dendrites, a strongly adapting firing pattern (AP frequency adaptation ratio, −93%), medium AP half-width (0.47 ms), high input resistance (300 MΩ), and a locally projecting axon (91% of the axon extended to the home column; group local 3 interneuron) (cf. Helmstaedter et al., 2008c) (for a detailed account of the identity of interneurons, compare Fig. 8 and Discussion).