Figure 4. The spatial firing rate pattern of 500 MCs in response to o-ethyl phenol. A, Patterns in the first seconds of odor exposure, before learning. MCs nos.356–360 have firing rates ∼40–50 Hz in response to the stronger inputs, whereas surrounding MCs, with weaker input signals, have much lower firing rates (purple arrows). Correspondingly, the MCs receiving weak input that are away from the strongly activated MCs also show relatively low firing rates (blue arrow), which are almost as low as the spontaneous firing rate (∼4 Hz) of MCs with no input. The bottom panel shows the spatial firing rate pattern of 10,000 GCs. MCs nos.356–360 have long lateral dendrites that cover the lateral connection to the GCs within no.4120–10,000, and some within no.0–20. A model MT cell is plotted in inverted black triangle, with lateral dendrite covered the range of GCs from ∼415 to 10,000, and the glomerulus plotted in green circle was activated by the input odor. B, Patterns in the 10th seconds, after learning. The strongly activated MCs have reduced the firing rates for strong inputs because of the lateral inhibition, while surrounding MCs nos. 210–500 are strongly suppressed by the lateral inhibition. Some MCs with weak inputs within this range even stop firing (purple arrows) because of the strong lateral inhibition effect. However, MCs with weak inputs out of this range display relatively enhanced responses (blue arrow) because of very weak feedback inhibition and no lateral inhibition. The GC displays a decreasing pattern of activity in the region surrounding the site where MCs are strongly activated.