A, voltage responses of an IRN to hyperpolarising and depolarising 1 s current steps of 4 pA per step, elicited from rest at −77 mV. Inward rectification is seen as relatively small voltage responses at hyperpolarised potentials (arrow) with each step and increasingly larger responses at more depolarised levels. The rectification ratio is 0.34. B, histogram of the inward rectification ratio for all neurons. Neurons with ratio below 0.5 form a population defined as IRNs and those above 0.5 as non-IRNs. C, plot of the input resistance (Rin) of IRNs and non-IRNs, measured at a hyperpolarised potential (−120 mV) and at resting membrane potentials. D, I–V plot of the steady-state voltage deflections to current steps of the neuron displayed in A. Note the steeper slope at more depolarised potentials. E, distribution of the resting membrane potentials of recorded neurons.