Table 1.

Criteria for unit and burst identification

Unit	Channel	Relative amplitude by channel	Timing	Start frequency (Hz)	End frequency (Hz)
B38	BN2	Medium, largest in protraction	Protraction	8	5
I2 (B31/B32, B61/B62)	I2	Largest	Protraction	10	5
B8a/b	RN	Largest	Retraction	3	3
B6/B9	BN2	Medium, 2nd largest in retraction	Retraction	10	5
B3	BN2	Largest overall	Retraction	8	2
B4/B5	BN3	Largest	Retraction	3	3

Frequency thresholds for burst initiation and termination were based on prior physiological studies and analyses (Morton and Chiel, 1993a; Hurwitz et al., 1996; McManus et al., 2014; Lu et al., 2015; Cullins et al., 2015b). These values were tried for all animals first and used if they yielded distinct bursts. In a few cases, exceptions had to be made in which frequencies were lowered for specific units in specific animals that tended to have unusually low firing rates. Named pairs of neurons (B8a/b, B6/B9, and B4/B5) are pairs of neurons that are difficult to distinguish from extracellular nerve recordings alone but are similar enough in their function to group together.