Recording yield at scale

The fraction of implanted electrode sites that actually return a usable signal — typically defined as a well-isolated single unit, or at least a reliable multiunit or field signal. Yield is the quantity that matters for real bandwidth, and it is almost always far below the nominal channel count: many sites see no neuron within reach, others are lost to encapsulation, drift, or hardware failure.

Yield falls along two axes that both worsen with scale. Spatially, packing more sites into fixed tissue reaches the point where extra sites oversample the same cells. Temporally, yield decays over weeks to years as the foreign-body response walls off electrodes; chronic single-unit yield in humans and primates is a central, honestly-reported limitation, not a solved problem. Reporting a device by its site count rather than its sustained yield is a common source of overclaiming.