Figure 5.

Scaling network size changes unitary strength per synapse and the functional coupling between pairs of neurons. A, mEPSCs were recorded postsynaptically via whole-cell patch clamp in the presence of TTX in either a large or small network. Calibration: 20 pA, 64 ms. B, Cumulative density functions depicting distributions of mEPSC amplitudes recorded from large and small networks. A rightward shift is observed in mEPSC amplitudes recorded from small networks. C, Average mEPSC amplitudes for neurons recorded in each size network show an increase in mean event amplitude in small networks relative to larger ones. D, Average mEPSC frequency for neurons recorded in each size network. mEPSC frequency was not significantly different in the two types of networks, despite a reduced number of synapses in the small network (Fig. 3C). E, The extent to which pairs of neurons were functionally coupled was assessed via evoked synaptic transmission using dual intracellular patch clamp. Action potentials were elicited in one “presynaptic” neuron whereas the synaptic response was measured in voltage clamp in the second “postsynaptic” neuron. F, Typical evoked transmission (stimulus artifacts replaced with arrows) in small networks was significantly increased in amplitude compared with evoked transmission in large networks. G, Quantification for all evoked transmission in large and small networks. Evoked responses in small networks were significantly larger than evoked responses in large networks. Note that pairs where evoked transmission in one neuron triggered an action potential in the postsynaptic neuron were omitted, because such depolarizations were too large to quantify in voltage clamp with our patch circuits. Although presynaptically induced spiking was rare in large networks, it was relatively common in small networks. ***p < 0.001. Error bars indicate SEM.