Unit

A unit is an inferred neuron whose spike activity is detected via extracellular recording using microelectrodes or neural probes. Units are the fundamental entities in spike-sorted data.

Single unit: A unit whose extracellular spike waveform is distinct enough that it likely originates from a single nearby neuron. Single-unit isolation is the gold standard for studying individual neuron behavior.

Multi-unit: A cluster of spike waveforms detected at one or more sites that cannot be confidently ascribed to individual neurons. Multi-unit activity reflects local population firing and is useful for studying aggregate neural activity.

Why it matters: The distinction between single-unit and multi-unit activity determines what scientific questions can be answered. Single units support analyses of individual neuron properties (tuning curves, response latencies), while multi-unit activity reveals population-level patterns.