Exponential Integrate-and-Fire

$$\tau \frac{\text{d}}{\text{d}t}u=-(u-u_{\mathrm{r}\mathrm{e}\mathrm{s}\mathrm{t}})+{\mathrm{\Delta }}_T\exp \left(\frac{u-{\theta }_{rh}}{{\mathrm{\Delta }}_T}\right)+RI$$

Default parameters: $\tau =10$ ms, ${\mathrm{\Delta }}_T=3$ mV, ${\theta }_{rh}=-50mV$, $u_{rest}=-65$ mV, $R=10M\mathrm{\Omega }$, $I=2.2nA$, firing threshold $u_{thr}=-45mV$.