Perielectrode neuronal loss (kill zone)

Perielectrode neuronal loss is the depletion of viable, firing neurons in the immediate annulus around a chronic shank, informally called the kill zone. Sustained inflammation, blood-brain-barrier leakage, local ischemia from severed microvessels, and mechanical strain together drive neuronal death and dendritic pruning within roughly the first 100 micrometers.

This loss matters far more than its spatial extent suggests because extracellular spike amplitude falls off steeply with distance (about 1/r for an idealized point source, and faster in practice for the dominant dipolar field). Losing the very closest neurons therefore disproportionately reduces the count of well-isolated single units, even when healthier neurons persist a little farther out.