Figure 2.

Supralinear increase of inhibition. (a) Simultaneous recording from three layer 2/3 pyramidal cells (PC1, blue; PC2, black; PC3, green). Left, a train of action potentials in PC2 elicits no current in PC1 nor PC3 (V_H, −40 mV). Middle, a train of action potentials in PC3 elicits no current in PC1 or PC2 (V_H, −40 mV). Right, simultaneous trains of action potentials in PC2 and PC3 elicit an outward current in PC1. All current traces are averages of multiple sweeps. (b) Same recording configuration as in a (different cells). Left, the spiking of either PC2 or PC3 alone elicits outward currents in PC1. Note the earlier onset of inhibition in PC1 (blue trace) when PC2 and PC3 are spiking simultaneously (the PC2-PC1 pair is the same one as in Fig. 1a). Right top, gray trace: algebraic sum of the currents elicited in PC1 in response to the spiking of PC2 and PC3 alone. Blue trace, outward current elicited in response to the simultaneous spiking of PC2 and PC3. Right bottom, running integral of the two currents illustrated on top. Note that the inhibitory charge in response to the simultaneous spiking of PC2 and PC3 is larger than the inhibitory charge of the algebraic sum of the responses of PC1 to the spiking of PC2 and PC3 alone. All current traces are averages of multiple sweeps. (c) Cumulative distribution of the nonlinearity index (see Results for details) for 38 similar experiments. Note that most values are larger than 0, indicating supralinear increase in recurrent inhibition when PC2 and PC3 are spiking simultaneously.