1. Experiment Seven: Spike Referencing

2. Voltage is the difference in electrical potential between two points (like your hair and the comb)….

3. and like the difference between electrical environment around recording electrode and reference electrode

4. Differential recordings: voltage = difference between recording and ground electrode. If “perfect ground”, voltage = potential at recording electrode. However…

5. In biology, there is no such thing as the perfect ground! http://tinyurl.com/7qcz5kshttp://tinyurl.com/73lwcbu Everywhere in your body there’s an electrical signal of some sort, so care must be taken choosing your ground to minimize this.

6. Procedure: put recording electrode in femur and ground electrode in coxa When you touch the barbs on the leg, make note of the level of “background activity” vs. individual spikes.

7. Procedure: Move ground electrode from coxa to the femur When you touch the barbs on the leg, is there a difference in the ratio of “background activity” vs. individual spikes?

8. Procedure: Move both electrodes to coxa What do you notice this time?