Spike

A spike is an action potential recorded with an extracellular electrode or neural probe site, typically 0.8–1.5 ms in duration. Spikes are identified by their waveform shape, which depends on neuronal morphology and recording geometry.

Why it matters: Spikes are the observable events that spike sorting algorithms cluster into putative single neurons. The quality of spike detection directly determines the scientific value of a recording.

Waveform characteristics: Extracellular spike waveforms are biphasic or triphasic, with shape determined by the neuron's size, type, distance from the electrode, and the electrode's impedance. Different neuron types (pyramidal, interneuron) produce characteristic waveform signatures.

Detection pipeline: Raw signal → bandpass filter (300–6000 Hz) → threshold detection → waveform extraction → spike sorting → single-unit isolation.