tetrode

A tetrode is an electrical device consisting of four closely spaced electrodes. The term is used in different contexts to describe separate technologies that share the same four-electrode concept, most notably in vacuum tube technology and in neuroscience for neural recording.

In vacuum tube technology, a tetrode refers to a four-element vacuum tube used as an amplifier or switching device. The four electrodes typically include the cathode (electron source), control grid, screen grid, and the suppressor grid or anode, arranged to control electron flow. The additional grids provide higher gain and reduce surface secondary emission effects compared to earlier triode tubes. Tetrodes were widely used in radio frequency and audio equipment before being largely superseded by pentodes and later solid-state technologies.

In neuroscience, tetrodes are four-contact microelectrode assemblies used for extracellular recording of neuronal activity. The four closely spaced recording contacts on a single shank allow simultaneous monitoring of action potentials from nearby neurons. By comparing spike waveforms across the four channels, researchers can improve spike sorting and distinguish activity from multiple neurons in a small brain region. Tetrodes are commonly made from materials such as platinum-iridium or tungsten and are often mounted on microdrives for adjustable depth, enabling chronic implantation in animals and, less frequently, in humans for research.

Today, the term “tetrode” typically denotes either the four-electrode vacuum tube or the four-contact neural electrode, depending on the field. Both concepts emphasize four interacting electrodes to modulate or record electrical signals.