Extracellular Recordings

Extracellular Recordings

Extracellular recordings are recordings of electrical potentials produced by a cell, either in extracellular fluid near the cell of interest, or non-invasively. These types of recordings can be divided into three main groups; single/multiple unit recordings, whole nerve recordings, and field potentials.

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Signal Overview

In extracellular electrophysiological recordings, an electrode is not inserted into a single cell, instead the electrode(s) are place in the extracellular fluid, near the cell of interest. The type of recording will depend on the type and size of the electrode, and proximity to the signal origin. 

Single/Multiple Unit Recordings
In these types of extracellular recordings of action potentials, instruments sample the electrical activity of a single neuron or several neurons at once. Recorded activity is referred to as unit as you cannot be sure if spikes are in fact action potentials. Recordings can be made either in vivo or in vitro. To record these types of signals, a glass or metal electrode with relatively high impedance is used alongside a headstage with high input impedance. If the electrode is very small (+ 1um tip), the activity of a single adjacent neuro can be recorded. If a slightly larger tip is used, it will record the activity of several neurons adjacent to the electrode, and spike sorting needs to be employed to identify particular cells. 

Epithelial Voltage Clamping (and Ussing Chambers)
In order to measure the transport of electrolytes, non-electrolytes and H2O across an epithelial membrane, an Ussing chamber setup is required. The chamber isolates each side of the membrane so that they face a separate chamber half so that chemical and electrical adjustments can be made to each side separately. With a Ussing setup (usually comprising a chamber, a perfusion system, an amplifier, and an acquisitions and analysis system), measurements can be taken from native tissue including stomach, large and small intestines, gall and urinary bladder, skin and trachea, as well as from tissue derived cell monolayers from various sources including renal tubes, pancreas, and salivary and sweat glands.

Whole Nerve Recordings
Many researchers are interested in recording the activity of peripheral nerves, which are essentially bundles of axons. This can be done with wired methodology where an electrode (usually silver wire) is placed in contact with the nerve in question. Another methodology is through the use of telemetry products where sympathetic nerve activity can be recorded. 

Field Potentials
Field potentials are probably the most common extracellular signals being recorded and include ECG, EMG and EEG.  With an electrode with an even bigger sampling field, the activity of individual neurons can no longer be distinguished, but rather a field potential generated by the activity of many cells. Extracellular field potential recording can either be carried out invasively or non-invasively on the skin.


Enabling Discovery


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Noise Elimination

This is a common issue in electrophysiology as you are dealing with very small signals as well as high impedance and capacitance of electrodes. All of ADInstruments hardware optimized with high quality noise specifications, but it is always good to have a few other tricks up your sleeve to help in your setup. 

  1. Ensure all electronic equipment used in recording setup is plugged into the same wall socket by using a fused multibox
  2. Ensure all shielding is connected to one grounding point or grounding bar. This will eliminate the risk of a grounding loop when different grounds are at slightly different potentials causing currents to flow in the shielding introducing noise.
  3. To identify the source of noise, strip back to the bare essentials, like the amplifier and acquisition and then systematically switch on additional equipment.
  4. Always try to eliminate the source of noise first, but if this isn’t possible then mask with shielding.
  5. Try and keep lead wires as short as possible and not looped. If they are long, try braiding them to prevent magnetically induced currents.
  6. Even fluid filled tubing for perfusions can act as antennas. If this is the case, shield with tin foil and connect to the metal grounding bar. 

Features and Add-Ons

Additional acquisition and analysis options to support your Extracellular Recordings analysis:

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Thank you for your interest in Extracellular Recordings. Please complete and submit the form below and an ADInstruments representative will aim to get in touch within one working day. If you’d like to speak to someone immediately, office contact information is available from the contact page.