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.