Single unit recording

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Single unit recording refers to the use of an electrode to record the electrophysiological activity (action potentials) from a single neuron.

An electrode introduced into the brain of a living animal will detect electrical activity that is generated by the neurons adjacent to the electrode tip. If the electrode is a microelectrode, with a tip size of 3 to 10 microns, the electrode will often isolate the activity of a single neuron. The activity consists of the voltages generated in the extracellular matrix by the current fields outside the cell when it generates an action potential. Recording in this way is generally called "single unit" recording. The recorded action potentials look very much like the action potentials that are recorded intracellularly, but the signals are very much smaller (typically about 0.1 mV). Most recordings of the activity of single neurons in animals are made in this way. Recordings of single neurons in living animals have provided important insights into how the brain processes information, following the hypothesis put forth by Edgar Adrian that unitary action potential events are the fundamental means of communication in the brain. For example, David Hubel and Torsten Wiesel recorded the activity of single neurons in the primary visual cortex of the anesthetized cat, and showed how single neurons in this area respond to very specific features of a visual stimulus. Hubel and Wiesel were awarded the Nobel Prize in Physiology or Medicine in 1981.

Microelectrodes used for extracellular single unit recordings are usually very fine wires that are insulated except at their extreme tip, and less often are glass micropipettes filled with a weak electrolyte solution similar in composition to extracellular fluid.