Liquid Crystal Alignment on Carbonaceous Surfaces with Orientational Order

SDs. 26. The latency of the single-axon EPSPs was measured between the peak of the presynaptic action potential and the beginning of the synaptic potential. Average synaptic responses were obtained after aligning the traces by the peak of the presynaptic action potential. Spikes were generated in the pyramidal cells by injecting a brief pulse (3 to 5 ms, 1 nA) of current. 27. Z. F. Mainen, T. J. Sejnowski, Science 268, 1503 (1995). 28. To generate the uncorrelated random currents, a Poisson train (2000 Hz) was convolved with the waveform of a single-axon EPSC, and the result was combined with the convolution of a Poisson train (1000 Hz) and a single-axon IPSC waveform. The waveforms of the synaptic currents were previously recorded (13). Trials were separated by 1 to 3 s. 29. PSTHs were built from 200 to 1300 trials. Data were aligned to the peak of the presynaptic spike before constructing the PSTH. To determine the beginning and the end of the PSTH peak, a cumulative sum of the histogram was built after subtracting the baseline spike frequency (31). The baseline was defined as a 50-ms period preceding the presynaptic spike. 30. At a holding potential of —70 mV, presynaptic spikes produced unitary EPSCs with an average rise time (10 to 90 %) of 0.43 6 0.06 ms and a weighted decay time constant of 1.9 6 0.3 ms [n 5 6 pairs (Fig. 2A)]. The mean peak amplitude was 185 6 pA (range, 28 to 488 pA; n 5 6 pairs). The corresponding unitary EPSPs recorded at resting conditions (; —73 mV ) had a rise time of 0.77 6 0.12 ms and a weighted decay time constant of 9.4 6 0.9 ms [n 5 7 pairs (Fig. 2A)]. The mean peak amplitude was 5.3 mV (range, 0.9 to 16.7 mV ). The decay time course of unitary EPSCs and EPSPs was fitted with a biexponential function. The weighted decay time constant was calculated as tw 5t 1 3 A1 1t 2 3 A2, where t1 and t2, and A1 and A2 represent, respectively, the time constant and relative amplitude of each exponential component.