Table 1. Responses of VB Neurons to Formalin Induced Pain before Normalization.
| Tonic | Burst Spike | ||
| Baseline | FR (Hz) | 6.53±0.75 | 0.38±0.06 |
| (−10∼0 min) | ISI (s) | 0.35±0.05 | 20.63±4.00 |
| ratio (%) | 94 | 6 | |
| 1st phase | FR (Hz) | 8.60±0.57 | 0.10±0.01 |
| (0–10 min) | ISI (s) | 0.22±0.02 | 33.23±4.35 |
| ratio (%) | 99 | 1 | |
| Early 2nd | FR (Hz) | 7.76±0.35 | 0.19±0.02 |
| phase | ISI (s) | 0.28±0.03 | 30.03±2.57 |
| (10–35 min) | ratio (%) | 98 | 2 |
| Late 2nd | FR (Hz) | 4.88±0.31 | 0.62±0.05 |
| phase | ISI (s) | 0.59±0.06 | 13.00±1.27 |
| (35–60 min) | ratio (%) | 89 | 11 |
Baseline is the spontaneous neural activity before formalin injection. Neural response after formalin injection is divided into the 1st and 2nd phases based on the quiescent interval between the two peaks of the behavioral pain responses. Early and late phase division in the 2nd phase is also based on the same rationale. n = 48 neurons, 7 mice. All values are mean±SEM. FR: firing rate, ISI: inter-spike-interval, ratio: percentage of respective firing modes from the total number of spikes.