Single unit recording
Encyclopedia
In neurophysiology
and neurology
, single-unit (or single-cell) recording is the use of an electrode
to record the electrophysiological
activity (action potential
s) from a single neuron
.
's experiments studying "animal electricity" that nerves transmitted electrical signals, but it was not until 1925, when Edgar Adrian used the newly invented vacuum tube amplifier
, that action potentials were recorded from nerve fibers. Adrian proposed that unitary action potential events are the fundamental means of communication in the brain, making the recordings of single neurons in living animals a source of key evidence as to how the brain processes information. David Hubel and Torsten Wiesel
recorded the activity of single neurons in the primary visual cortex of anesthetized cats, 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.
single-unit recordings are usually very fine wires made from tungsten or platinum-iridium alloys that are insulated except at their extreme tip. Glass micropipette
s that are filled with a weak electrolyte
solution, similar in composition to extracellular fluid
, can be used. Subtle differences in microelectrode shape and composition benefit different tasks. For instance, the use of low impedance electrodes (< 1MOhm) is favourable for mapping gross regions of grey matter
and white matter
because they pick up more signal from surrounding neurons, albeit at the expense of focusing on the activity of individual cells for which higher impedance microelectrodes are used.
Isolated neural activity can be recorded from anesthetized or awake animals. In the latter, the link between brain activity and behavior can be studied. The procedure is not painful because the brain has no internal pain receptors.
s adjacent to the electrode tip. If the electrode is a microelectrode, with a tip size of 3 to 10 micrometres, 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).
. Electrical current manipulates the activity of local neural populations, which influences the animal's behavior.
Neurophysiology
Neurophysiology is a part of physiology. Neurophysiology is the study of nervous system function...
and neurology
Neurology
Neurology is a medical specialty dealing with disorders of the nervous system. Specifically, it deals with the diagnosis and treatment of all categories of disease involving the central, peripheral, and autonomic nervous systems, including their coverings, blood vessels, and all effector tissue,...
, single-unit (or single-cell) recording is the use of an electrode
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit...
to record the electrophysiological
Electrophysiology
Electrophysiology is the study of the electrical properties of biological cells and tissues. It involves measurements of voltage change or electric current on a wide variety of scales from single ion channel proteins to whole organs like the heart...
activity (action potential
Action potential
In physiology, an action potential is a short-lasting event in which the electrical membrane potential of a cell rapidly rises and falls, following a consistent trajectory. Action potentials occur in several types of animal cells, called excitable cells, which include neurons, muscle cells, and...
s) from a single neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
.
History
It has been known since Luigi GalvaniLuigi Galvani
Luigi Aloisio Galvani was an Italian physician and physicist who lived and died in Bologna. In 1791, he discovered that the muscles of dead frogs legs twitched when struck by a spark...
's experiments studying "animal electricity" that nerves transmitted electrical signals, but it was not until 1925, when Edgar Adrian used the newly invented vacuum tube amplifier
Valve amplifier
A valve amplifier or tube amplifier is a type of electronic amplifier that makes use of vacuum tubes to increase the power and/or amplitude of a signal. Low to medium power valve amplifiers for frequencies below the microwaves were largely replaced by solid state amplifiers during the 1960s and...
, that action potentials were recorded from nerve fibers. Adrian proposed that unitary action potential events are the fundamental means of communication in the brain, making the recordings of single neurons in living animals a source of key evidence as to how the brain processes information. David Hubel and Torsten Wiesel
Torsten Wiesel
Torsten Nils Wiesel was a Swedish co-recipient with David H. Hubel of the 1981 Nobel Prize in Physiology or Medicine, for their discoveries concerning information processing in the visual system; the prize was shared with Roger W...
recorded the activity of single neurons in the primary visual cortex of anesthetized cats, 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
Nobel Prize in Physiology or Medicine
The Nobel Prize in Physiology or Medicine administered by the Nobel Foundation, is awarded once a year for outstanding discoveries in the field of life science and medicine. It is one of five Nobel Prizes established in 1895 by Swedish chemist Alfred Nobel, the inventor of dynamite, in his will...
in 1981.
Procedure
Microelectrodes used for extracellularExtracellular
In cell biology, molecular biology and related fields, the word extracellular means "outside the cell". This space is usually taken to be outside the plasma membranes, and occupied by fluid...
single-unit recordings are usually very fine wires made from tungsten or platinum-iridium alloys that are insulated except at their extreme tip. Glass micropipette
Micropipette
A micropipette is one of two different instruments used in science laboratories.-History:The first micropipette was patented in 1960 by Dr Hanns Schmitz . The founder of the company Eppendorf, Dr...
s that are filled with a weak electrolyte
Electrolyte
In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....
solution, similar in composition to extracellular fluid
Extracellular fluid
Extracellular fluid usually denotes all body fluid outside of cells. The remainder is called intracellular fluid.In some animals, including mammals, the extracellular fluid can be divided into two major subcompartments, interstitial fluid and blood plasma...
, can be used. Subtle differences in microelectrode shape and composition benefit different tasks. For instance, the use of low impedance electrodes (< 1MOhm) is favourable for mapping gross regions of grey matter
Grey matter
Grey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil , glial cells and capillaries. Grey matter contains neural cell bodies, in contrast to white matter, which does not and mostly contains myelinated axon tracts...
and white matter
White matter
White matter is one of the two components of the central nervous system and consists mostly of myelinated axons. White matter tissue of the freshly cut brain appears pinkish white to the naked eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color is due to...
because they pick up more signal from surrounding neurons, albeit at the expense of focusing on the activity of individual cells for which higher impedance microelectrodes are used.
Isolated neural activity can be recorded from anesthetized or awake animals. In the latter, the link between brain activity and behavior can be studied. The procedure is not painful because the brain has no internal pain receptors.
Electrical activity
An electrode introduced into the brain of a living animal will detect electrical activity that is generated by the neuronNeuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s adjacent to the electrode tip. If the electrode is a microelectrode, with a tip size of 3 to 10 micrometres, the electrode will often isolate the activity of a single neuron. The activity consists of the voltages generated in the extracellular matrix
Extracellular matrix
In biology, the extracellular matrix is the extracellular part of animal tissue that usually provides structural support to the animal cells in addition to performing various other important functions. The extracellular matrix is the defining feature of connective tissue in animals.Extracellular...
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).
Electrical stimulation
Causal relationships can be established by passing current through the microelectrode, a technique known as microstimulationMicrostimulation
Microstimulation is a technique that stimulates a small population of neurons by passing a small electrical current through a nearby microelectrode.-Applications:...
. Electrical current manipulates the activity of local neural populations, which influences the animal's behavior.
See also
- Brain implant
- Brain–computer interface
- BrainGateBrainGateBrainGate is a brain implant system developed by the bio-tech company Cyberkinetics in 2008 in conjunction with the Department of Neuroscience at Brown University. The Braingate technology and related Cyberkinetic’s assets are now owned by privately held Braingate, LLC...
- Chronic electrode implantsChronic Electrode ImplantsChronic Electrode Implants are electronic devices implanted into the brain. They may record electrical impulses in the brain or they may stimulate neurons with electrical impulses from an external source.- Clinical applications and direction :...
- Deep brain stimulationDeep brain stimulationDeep brain stimulation is a surgical treatment involving the implantation of a medical device called a brain pacemaker, which sends electrical impulses to specific parts of the brain...
- Electrical brain stimulationElectrical brain stimulationElectrical brain stimulation , also referred to as focal brain stimulation , is a form of electrotherapy and technique used in research and clinical neurobiology to stimulate a neuron or neural network in the brain through the direct or indirect excitation of its cell membrane by using an electric...
- ElectrocorticographyElectrocorticographyElectrocorticography is the practice of using electrodes placed directly on the exposed surface of the brain to record electrical activity from the cerebral cortex. ECoG may be performed either in the operating room during surgery or outside of surgery...
- ElectroencephalographyElectroencephalographyElectroencephalography is the recording of electrical activity along the scalp. EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain...
- ElectrophysiologyElectrophysiologyElectrophysiology is the study of the electrical properties of biological cells and tissues. It involves measurements of voltage change or electric current on a wide variety of scales from single ion channel proteins to whole organs like the heart...
- Intracranial EEGIntracranial EEGIntracranial EEG is an invasive technique based on recording electroencephalography signals directly from the human cortex, as opposed to surface recordings in scalp-EEG...
- Multielectrode arrayMultielectrode arrayMultielectrode arrays or microelectrode arrays are devices that contain multiple plates or shanks through which neural signals are obtained or delivered, essentially serving as neural interfaces that connect neurons to electronic circuitry...