Editing Electrophysiology (section)

==Extracellular recording==

===Single-unit recording===
{{Main|single-unit recording}}
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 about 1 micrometre, the electrode will usually detect the activity of at most one neuron. Recording in this way is in general called "single-unit" recording. The action potentials recorded are very much like the action potentials that are recorded intracellularly, but the signals are very much smaller (typically about 1 mV). Most recordings of the activity of single neurons in anesthetized and conscious animals are made in this way. Recordings of single neurons in living animals have provided important insights into how the brain processes information. 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.<ref>{{cite journal |pmid=14449617 |url=http://www.jphysiol.org/cgi/pmidlookup?view=long&pmid=14449617 |title=Receptive fields, binocular interaction and functional architecture in the cat's visual cortex |date=1962-01-01 |author1=D. H. Hubel |journal=The Journal of Physiology |volume=160 |issue=1 |pages=106–54 |last2=Wiesel |first2=TN |pmc=1359523 |doi=10.1113/jphysiol.1962.sp006837}}</ref> Hubel and Wiesel were awarded the Nobel Prize in Physiology or Medicine in 1981.<ref>{{cite web|url=http://nobelprize.org/nobel_prizes/medicine/laureates/1981/|title=The Nobel Prize in Physiology or Medicine 1981|website=nobelprize.org|access-date=5 May 2018|url-status=live|archive-url=https://web.archive.org/web/20171223143417/https://www.nobelprize.org/nobel_prizes/medicine/laureates/1981/|archive-date=23 December 2017}}</ref>

To prepare the brain for such electrode insertion, delicate slicing devices like the compresstome vibratome, leica vibratome, microtome are often employed. These instruments aid in obtaining precise, thin brain sections necessary for electrode placement, enabling neuroscientists to target specific brain regions for recording.<ref>{{cite journal | pmc=5856250 | date=2018 | last1=Papouin | first1=T. | last2=Haydon | first2=P. G. | title=Obtaining Acute Brain Slices | journal=Bio-Protocol | volume=8 | issue=2 | pages=e2699 | pmid=29552595 }}</ref>

===Multi-unit recording===
If the electrode tip is slightly larger, then the electrode might record the activity generated by several neurons. This type of recording is often called "multi-unit recording", and is often used in conscious animals to record changes in the activity in a discrete brain area during normal activity. Recordings from one or more such electrodes that are closely spaced can be used to identify the number of cells around it as well as which of the spikes come from which cell. This process is called [[spike sorting]] and is suitable in areas where there are identified types of cells with well defined spike characteristics.
If the electrode tip is bigger still, in general the activity of individual neurons cannot be distinguished but the electrode will still be able to record a field potential generated by the activity of many cells.

===Field potentials===
[[File:Field potential schematic.jpg|thumb|400px|A schematic diagram showing a field potential recording from rat hippocampus. At the left is a schematic diagram of a [[presynaptic terminal]] and postsynaptic neuron.  This is meant to represent a large population of synapses and neurons.  When the synapse releases glutamate onto the postsynaptic cell, it opens ionotropic glutamate receptor channels.  The net flow of current is inward, so a current sink is generated.  A nearby electrode (#2) detects this as a negativity.  An ''intracellular'' electrode placed inside the cell body (#1) records the change in membrane potential that the incoming current causes.]]
[[Extracellular field potential]]s are local current sinks or sources that are generated by the collective activity of many cells.  Usually, a field potential is generated by the [[neural synchronization|simultaneous activation]] of many neurons by [[synaptic transmission]].  The diagram to the right shows hippocampal synaptic field potentials.  At the right, the lower trace shows a negative wave that corresponds to a current sink caused by positive charges entering cells through postsynaptic [[glutamate receptor]]s, while the upper trace shows a positive wave that is generated by the current that leaves the cell (at the cell body) to complete the circuit.  For more information, see [[local field potential]].

===Amperometry===
[[Amperometry]] uses a carbon electrode to record changes in the chemical composition of the oxidized components of a biological solution. Oxidation and reduction is accomplished by changing the voltage at the active surface of the recording electrode in a process known as "scanning". Because certain brain chemicals lose or gain electrons at characteristic voltages, individual species can be identified. Amperometry has been used for studying exocytosis in the nervous and endocrine systems. Many monoamine [[neurotransmitters]]; e.g., [[norepinephrine]] (noradrenalin), [[dopamine]], and [[serotonin]] (5-HT) are oxidizable. The method can also be used with cells that do not secrete oxidizable neurotransmitters by "loading" them with 5-HT or dopamine.