In article <60634 at sdcc12.ucsd.edu>, wsun at jeeves.ucsd.edu (Fiberman) wrote:
> For the electrophysiologists out there: What is meant by single
> unit and multiple unit recordings? This is in reference to
> recording activity from cells in the brain.
Microelectrodes can be placed in the brain to record extracellularly from
neurons in the vicinity of their tips. Typically currents generated by
action potential events in several cells close to the tip produce voltage
changes detectable through the electrode. A number of parameters of the
electrode determine what signals are picked up. Low-impedance electrodes
sample from a larger volume and pick up smaller amplitude signals from many
cells. This often takes the form of "hash", generalized neural activity not
resolvable into action potentials. When spikes can be seen, they often
arise from several cells, distinguishable by the size and shape of the
action potential waveforms. This is multiunit activity. When one of these
spikes can be isolated, either through luck, electrode characteristics
(high impedance electrodes record from a smaller volume, picking up cells
less often, but when they record cells they are generally well-isolated),
or filtering and window-discrimination, you have single unit recording.
Each of these has its place. Single unit recording is useful when studying
single cells, of course. Multiunit recording can be appropriate for mapping
studies, for instance. Hash is nice for figuring out where you are!
saul+ at pitt.edu