Rhythmic motor patterns are found throughout all living organisms and are responsible for maintaining some of our most fundamental behaviors. The motor circuits producing these behaviors are flexible and able to adapt to changing internal and environmental conditions, yet stable enough to maintain function within certain boundaries. Central pattern generators (CPGs), which are the primary source of this stability, reliably maintain activity patterns and thus the behaviors they drive. The crab stomatogastric nervous system contains the well-characterized gastric mill (chewing) and pyloric (filtering of food) CPGs. In vitro, the pyloric rhythm is stereotyped with little variation over time. Temperature, inter-circuit interactions and neuromodulation can influence the rhythm, but most variation occurs between individuals, not within (Tang et al., 2012; Bucher et al.,). In vivo , the range of variation of the rhythm and the extent of external influences are, with few exceptions unknown (Hedrich et al., 2011; Soofi et al., 2014).;Using long-term recordings at constant temperature we identified the range and sources of variability of the pyloric and gastric mill rhythms In vivo. A 12 hour light-driven cycle influences the frequency of both the pyloric and gastric mill rhythms, however this can be overridden by other sensory influences, including feeding. Feeding also alters the structure of the pyloric rhythm as well as increases its frequency. The pyloric and gastric mill rhythms also exhibit intercircuit interactions consistent with those previously observed in vitro (Marder et al., 2005). Non-canonical rhythms which had previously not been shown to occur naturally were also observed.
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