FIGURE 2. Properties of EPSP enhancement.

a, Plotting the average amplitude of the evoked EPSP versus the somatic membrane potential of the presynaptic neuron reveals continuous functions that are well fitted with a linear function (n = 5 pairs). To the right of each trace is the per cent enhancement of the EPSP recorded at the most depolarized, versus the most hyperpolarized, membrane potentials tested. Points show mean s.e.m. b, Two examples of histogram EPSP amplitude distributions at hyperpolarized and depolarized membrane potentials (following the protocol in Fig. 1a; both pairs show a significant shift, P < 0.01). The black line illustrates the level of baseline activity, using our measure of synaptic amplitude (see Methods). c, Depolarization significantly (P < 0.01) shifts the normalized EPSP amplitude histogram (n = 15 pairs) to the right. Normalization was performed by fitting the hyperpolarized amplitude distribution of each cell with a gaussian curve and then plotting the data such that the mean of the hyperpolarized state was 0 and the standard deviation was 1.