The utility of Granger Causality analysis (GCA) as a tool for gauging connectivity is dependent on the nature of neural activity. (a) Schematic of the pyloric network. Links denote inhibitory synapses, with color signifying direction. (b) Activity (schematic) of AB/PD and PY neurons in a model of this network where the activity of AB/PD and PY neurons is arrhythmic or non-oscillatory. When GCA was used, it correctly predicted a functional connectivity from PD to PY that matched known synaptic connectivity. (c) Activity (schematic) of AB/PD and PY neurons in a model where the activity of AB/PD and PY neurons is rhythmic or oscillatory, as in the naturally functioning circuit. Notably, although PD is not causally related to PY, activity of PD neurons followed activity of PY neurons. When GCA was used, it predicted a functional connectivity from PY to PD that did not match known synaptic connectivity. AB/PD, anterior burster/pyloric dilator; LP, lateral pyloric; PY, pyloric.