Introduction

Various forms of stimuli, including physical and chemical agents, are used by neurophysiologists in the study of excitable tissue. Electrical stimuli of pulsed voltage or current are generally the most controllable. Early investigators used batteries and devices such as the inductorium for galvanic and faradic stimulation; the vacuum tube had yet to be invented, so precisely controlled pulses were not available until the late 1930s. Grass pioneered the development of the square pulse stimulator for mapping the human cortex in the 1940s. Features such as twin pulse delivery for muscle and nerve refractory studies, remote stimulus isolation, and external synchronization were developed by Grass. Currently, there are two electrical stimulators offered; the SD9 and S48 and several accessory units for stimulus isolation, constant voltage, current delivery and electrode switching.

The S48 Stimulator is capable of delivering appreciable output current without the companion stimulus isolation units. The output is referred to ground, however. This may be suitable for transmural stimulation in vitro of one or perhaps two tissue bath preparations. For multiple baths greater output current is required.

The new S88X is a dual output, general purpose stimulator for nerve and muscle stimulation procedures with computer interface control. This new stimulator has touch-pad controls.

The development of EEG as a diagnostic tool prompted the design of a photic stimulator used in conjunction with the EEG examination for testing photic-induced abnormalities. The design requires precise, repetitive, short duration pulses of light with adjustable intensity. The Grass photic stimulator became the "standard" and an indispensable tool in other fields including electroretinography and ophthalmology. Currently, there arefive photic stimulators; the PS40 series and PS60/LED for clinical EEG investigation, FLC-LTM64 for use with the Beehive Horizon for long-term epilepsy monitoring, and the PS33-PLUS for research.

Important Notice:
Some time ago we reviewed all Grass stimulators and accessory stimulus isolation units and changed some wording in our literature regarding "human use" applications. Statements such as "For Research Only - Not Intended For Use on Humans" are placed on several devices in the catalog. This conservative wording was chosen due to the evolving safety standards for "medical" devices, especially with respect to harmonization of the standards with international requirements, like IEC-601. These newer standards make it very difficult, if not impossible, for a manufacturer to market a general purpose device for a variety of purposes, including basic research and clinical research, while still maintaining adherence to strict standards for clinical medical devices. Many Grass Stimulators were designed prior to the 1976 Medical Device Amendment to the U.S. Food and Drug law, so were "grandfathered" into being listed and cleared as "medical devices" in the U.S. With the current legal climate, the wide range of potential applications for these stimulators, and the requirement that they be used in conjunction with Grass Stimulus Isolation Units to be considered safe, the addition of the "human use" disclaimer was deemed appropriate and prudent.

In summary, Grass Stimulators and accessory Stimulus Isolation Units were designed to meet medical device standards and have a record of over a decade of safe use in clinical settings. They are manufactured in a FDA GMP compliant factory under strict medical device requirements. However, the changing medical regulatory environment compels us to leave the decision to use the products for human applications up to the user. Astro-Med, Inc. (May, 2011)