If electrodes only measure voltage, how does software know which neuron fired? · Lobeworks/17

By geometry: spike sorting.

If electrodes only measure voltage, how does software know which neuron fired?

By geometry: spike sorting. A neuron's extracellular potential falls fast with distance, so on a dense probe each spike appears on several neighbouring sites with different sizes, a footprint (template) that differs between cells tens of micrometres apart. Software such as Kilosort finds the spikes and groups them by footprint, one group per unit, the way several seismographs locate one earthquake. The electrode measures voltage; the neuron is found by geometry.