Figure 1.

Constancy of activity with variable currents. (a) Partial schematic diagram of the pyloric network of the crab Cancer borealis, including the pacemaker (AB), two pyloric dilator (PD), the lateral pyloric (LP), and the pyloric constrictor (PY) neurons. (b) Extracellular recordings from two pyloric motor nerves (lvn and pdn) from two different animals (the different color labels). Notice the different periods of the rhythmic activity. (c) Ionic currents I_A (top) and high-threshold potassium ion current, I_HTK (bottom) from PD neurons of the two preparations (red and orange) shown in panel (b). Notice the large amplitude differences. (d) Phase values (i.e., the proportion of the period, beginning with the first spike of the PD burst), for the end of PD burst (PD_off) and the beginning and end of LP burst (LP_on, LP_off) as indicated in panel (b), as a function of the period. The coefficient of variation (CoV) for each phase is indicated at the right. Note the low CoVs for each phase value; n = 9. (e) The maximal current levels (measured at the peak; e.g., the arrow in panel [c]) for intrinsic currents in PD: I_A, I_HTK, and I_h (top panel) and synaptic currents between PD and LP (bottom panel) as a function of the pyloric rhythm period in the same preparation as in panel (d). Note that the CoV values (right) are approximately one order of magnitude higher than those for the phase values shown in panel (d). The colored boxes in panels (d) and (e) highlight the phase and ionic current values, respectively, of the animals whose activity is shown in panel (b) and whose raw currents are shown in panel (c). Abbreviations: ms, milliseconds; nA, nanoamperes.