Figure 2.

Simultaneously recorded membrane potentials. A–C, Left, Simultaneous whole-cell current-clamp recordings from pairs of layer IV pyramidal cells both held at approximately −80, 0, and −50 mV. Holding cells at −80 mV reveal EPSPs (A), at 0 mV IPSPs (B), and at −50 mV a mixture of both (C). Note periods of low-amplitude (<5 mV) and high-amplitude (>5 mV) activity (orange and gray lines mark magnified regions of low- and high-amplitude epochs, respectively). During high-amplitude epochs, neurons receive highly correlated inputs. During low-amplitude epochs, neurons receive only occasional, simultaneous inputs (stars). A–C, Right, Voltage histograms from simultaneously recorded neurons at the three holding potentials. Secondary peaks in the histograms are marked by arrows. For convenience, membrane potentials that are >5 mV (dotted lines) above the mean (dashed lines) are classified as high-amplitude epochs (see text for more details).