Categorization of units based on firing properties and field locations
| Firing location | Number of units |
|---|---|
| Delay zone | 45 |
| Stem | 87 |
| Return arms | 35 |
| Reward arms | 17 |
| Pedestal/ramp | 58 |
| Sparse firing | 87 |
| Interneurons | 11 |
Sparse firing neurons emitted <100 spikes in a session. Pyramidal cells were distinguished from interneurons based on the shape of the interspike interval histogram, waveform shape, and firing rate (see Materials and Methods).