In this thesis, I use electrophysiological techniques to study the pyloric circuit of the stomatogastric ganglion (STG) in the crab, Cancer borealis. The pyloric circuit of the STG is a well studied neural circuit and is a particularly favorable preparation for relating changes in cellular processes to circuit dynamics and plasticity. Both experimental and theoretical investigations from the STG have suggested that similar circuit performance can arise from variable sets of circuit parameters. However, it is unclear to what extent are circuits composed of variable internal parameters robust to external perturbations.

For poikilotherms such as the crab, temperature is a behaviorally relevant perturbation and poses a considerable environmental challenge to the circuit. Not only does temperature influence the reaction rates of all cellular processes, including the ion channels and synapses that determine network activity, but it affects each of these cellular processes to a different degree. To understand which circuit features are stable or flexible to short-term temperature fluctuations, I subjected pyloric circuits to temperature ranges they normally encounter in the wild (from 7-23 ºC). Interestingly, while network frequency increased 4-fold over these temperature ranges, the phase relationships remained constant. To understand how temperature compensation of phase might occur, I used voltage-clamp to characterize the temperature dependence (Q₁₀'s) of the synapses and membrane currents involved in phase maintenance. We then used computational models to show that the experimentally measured Q10's promote phase maintenance.

To understand which circuit features are stable or plastic to long-term temperature perturbations, I acclimated animals for 3 weeks to either 7 ºC or 19 ºC. Remarkably, temperature acclimation did not alter either the circuit's frequency or phase relationships in response to acute temperature changes from 7-23 ºC. However, at temperatures outside this range (> than 23 ºC), the pyloric rhythm became less robust and often crashed. Interestingly, warm-acclimation significantly increased the robustness of circuit performance at extreme temperatures suggesting a shift in the circuit's operating range. Lastly, each preparation appeared to crash in a different way, as would be predicted if each individual animal's pyloric network is comprised of a different set of underlying circuit parameters.