NeuroNexus · neuronexus.com · Glossary
Detection Radius
The detection radius is the distance from an electrode site within which a neuron's spike is large enough to be picked out of the background, about a hundred micrometers for an extracellular site in cortex.
It is set by how quickly the extracellular spike falls off with distance, not by the electrode's design, and it is the single number from which most site-layout decisions follow.
A site sees a sphere of tissue about the size of that radius, so a shank samples a cylinder roughly two hundred micrometers across along its length however many sites it has. Adding sites within that cylinder does not reach new neurons; it sees the same neurons from more positions. That is the purpose of a tetrode or polytrode layout: sites spaced closer than the radius record one neuron with several amplitudes at once, and the pattern of amplitudes separates it from its neighbors. Sites spaced farther apart than the radius each sample a different population, which is what a linear layout at 100 µm pitch or a multi-shank layout at 200 µm shank spacing is for. Site pitch is chosen against the detection radius.
The radius also bounds yield. The number of neurons a probe can report is roughly the number of cell bodies inside its sampled volume that are firing, which is why yield varies more with the target structure than with the site count. Layouts are under Probe Geometry; the fall-off itself is under spike.
Typical values
| Detectable spike | within about 100 to 150 µm |
|---|---|
| Well-isolated single unit | within about 50 µm |
| Tissue sampled by one shank | a cylinder about 200 µm across |
Related Terms
Cite this term
NeuroNexus. "Detection Radius." NeuroNexus Glossary, updated 2026-10-12. https://www.neuronexus.com/resources/glossary/detection-radius