What does each electrode on a probe actually measure? · Lobeworks/17

The extracellular potential: the voltage of the fluid at its surface, measured against a reference electrode.

What does each electrode on a probe actually measure?

The extracellular potential: the voltage of the fluid at its surface, measured against a reference electrode. Nearby neurons push currents through the fluid when they fire, and because the fluid resists, those currents leave small voltage differences in it, tens to hundreds of microvolts close to a cell. The electrode does not detect a neuron or absorb a spike; it reads that voltage, and nothing else.