From a biological recording standpoint there are other issues. In an instrument design context most people think of isolation from ground as it relates to electrical safety. Stimulus isolators, as the name implies, also isolate a given stimulus from ground.
Stimulus artifact meaning series#
WPI isolators in the 300 and DLS series offer a compliance voltage of 100V with very low noise. Once this compliance voltage has been reached, further increases in tissue resistance will cause a drop in delivered current. The maximum amount of voltage that a constant current stimulator can provide is called the compliance voltage. If the resistance of the preparation becomes infinite, as might happen if one of the stimulating electrodes is removed from the tissue, the stimulator could not mount an infinite voltage to compensate. There is obviously a limit to how much voltage a constant current stimulator can provide. A constant current stimulator will "sense" resistance change and provide whatever voltage is needed to maintain delivery of current at the set rate. Second, stimulating electrodes tend to increase their resistance as stimulation progresses, as do some tissues.First, current is the quantity that stimulates most excitable tissues.Devices that hold voltage constant at a value set by the user and allow current to be determined by Ohm's law are known as constant voltage stimulators.Ĭonstant Current Stimulators - Devices that hold current constant at a value set by the user during the stimulation process and allow voltage to be determined by Ohm's law are called constant current stimulators.Ĭonstant current stimulators are preferred for two reasons:
Types of Stimulus DevicesĬonstant Voltage Stimulators - In the delivery of electrical energy to biological tissues, stimulus devices can hold either current or voltage constant during the stimulating process. More commonly, the resistance of tissue differs from sample to sample, and the resistance of the electrodes changes with applied current over time in a process called polarization. This simple equation shows that if voltage is constant, current flow will diminish if the tissue/electrode resistance goes up, and will increase if the resistance decreases. Where V is the applied voltage, I is the current and R is the electrical resistance of the tissue and or the stimulating electrodes. The two quantities are related by Ohm's law: V=IR Electrical stimulation of biological tissues involves the delivery of current and voltage to the stimulation site. The term stimulation refers to the delivery of energy of some kind to a biological tissue in order to elicit an observable response.Īlthough the energy used in stimulation may be chemical, thermal, mechanical or electrical, this discussion will focus on electrical stimulation. Isolated Stimulation and Stimulus Isolators
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