5.1 Leaky Integrate-and-Fire

1. Build the circuit shown in Figure 3. Have your TA check over the circuit to make sure your Arduino outputs aren’t shorted to ground or anything, or just go on to the next step if you’re confident in your circuitry skills. Make sure the ammeter is in series with the source of the injection current.
2. Connect your ‘scope to measure the voltage across the resistor in the RC circuit, and to take the trigger signal from the Arduino board.
3. Take a look at the Arduino program and take a minute to understand what it is doing, and the order it is doing those actions in. In particular, take note of the voltage threshold and the ‘dead time’ after each firing of the neuron, noted as  in the text.
4. Once the program is loaded onto the Arduino, you technically don’t need a PC anymore! Just power the Arduino using the transformer and press the reset button whenever you would like the program to restart and send the initializing trigger pulse. We’ll keep the PC so that you can edit the program and re-upload to the Arduino.
5. If the Arduino is working properly, you will see a train of pulses as the RC circuit charges up, reaches the threshold voltage and discharges, waits for the duration of , then starts charging again. You can use the cursors to measure the time between pulses and call that the wavelength of the pulse train.
6. You won’t be able to accurately measure the injection current while the RC circuit is constantly charging. To measure the injection current, set the threshold voltage to zero in the Arduino program. Think about why that works.
7. You should now have a pair of data – the applied injection current and resulting pulse frequency. Adjust the potentiometer to use a different injection current.
8. Continue taking data until you have enough to do a least-squares fit and trust the result.