Simultaneous patch-clamp recordings of spike activity from pairs of SCN neurons. The bath contained DNQX (20 μM), APV (50 μM), BIC (30 μM) to block fast synaptic transmission, and firing rate was adjusted to 4–10 Hz. (A) Cell-attached recordings of extracellular spike activity recorded from a pair of SCN neurons (upper trace cell 1, bottom trace cell 2) and the corresponding cross-correlogram (bin width, 20 ms). (B) Whole-cell recordings of sodium spikes recorded from a pair of SCN neurons (upper trace cell 1, bottom trace cell 2) and the corresponding cross-correlogram (bin width, 20 ms). (C) Whole-cell recordings of sodium and calcium spikes recorded in the presence of 4-AP from a pair of SCN neurons (upper trace cell 1, bottom trace cell 2) and the corresponding cross-correlogram (bin width, 20 ms). Cross-correlation analysis in A, B and C indicated asynchronous spike activity.