Abstract

All individual humans and animals are different. How well-tuned do brains need to be to produce behavior that we consider healthy and normal? This question has been difficult to study rigorously in animals with large brains, but small nervous systems with identified neurons and circuits have allowed us to ask this question in the past few years. Experimental work on the crustacean stomatogastric ganglion (STG) has revealed a 2-6 fold variability in many of the parameters that are important for circuit dynamics. These include the strength of the same synapse across animals, the conductance densities of many membrane currents, the copy numbers of the mRNA that encode those currents (Goaillard et al., Nat Neuroscience. 2009) and the structures of STG neurons. At the same time, a body of theoretical work shows that the similar network performance can arise from diverse underlying parameter sets (Prinz et al., Nat Neuroscience 2004; Gutierrez and Marder, 2013). Together, these lines of evidence suggest that each individual animal has found a different solution to producing “good enough” motor patterns for healthy performance in the world. These findings raise the question of the extent to which animals with different sets of underlying circuit parameters can respond reliably and robustly to environmental perturbations and neuromodulation. Consequently, we study the effects of temperature, pH and neuromodulation on the pyloric rhythm of crabs. We find that the signatures of how individual animals respond to extreme perturbations are quite different even when reliable and reproducible behaviors are seen in response to graceful perturbations, thus revealing the consequence of underlying parameter differences.