A microelectrode advanced into brain tissue can isolate the action potentials of an individual neuron. This single-unit recording technique provides the most direct measure of a cell’s output and has been foundational to systems neuroscience.

By correlating the neuron’s firing with sensory stimuli, behavioral events, or the activity of other cells, researchers infer the information that neuron encodes. Classic discoveries—orientation selectivity in visual cortex, place cells in the hippocampus, mirror neurons in premotor cortex—emerged from single-unit studies. The method can be used in anesthetized or awake, behaving animals and, under special circumstances, in human surgical patients.

Modern variants include multi-electrode arrays that sample dozens or hundreds of units simultaneously and juxtacellular recording that allows labeling of the recorded cell. Limitations include the difficulty of identifying cell type from extracellular waveforms alone and the sparse sampling of any given region. Despite the rise of optical methods, single-unit recording remains unmatched for temporal precision and spike-timing analyses.

• Records action potentials from individual neurons
• Links cellular activity to stimuli or behavior
• Foundation of many systems-level discoveries
• Now often combined with multi-electrode arrays