Figure 2.

Spontaneous electrical activity before birth. A, Spontaneously active SP neurons from three human subjects. Dashed lines, Resting potentials (−60, −62, and −63 mV, respectively). Asterisks indicate UP states with one or zero action potentials (APs). Inset, Duration (dur.) and amplitude (amp.) of an UP state. Parameters of UP states (n = 162 events, 25 neurons) are plotted using frequency histograms in B–D and F. B, The most frequent (mode) plateau amplitude was 19 mV. C, The most frequent plateau duration was 0.9 s. D, Variability in time interval between successive UP states. The most common interval was 3 s. E, Expanded fragment of trace 2 shown in A. The high-frequency–accommodating AP burst “Q” is followed by low-frequency–regular firing AP burst “R.” F, During plateau depolarizations SP neurons experience a wide range of AP firing frequencies. The most common AP firing rate was 4 Hz.