- 1. A stimulant. 2. That which can elicit or evoke action (response) in a muscle, nerve, gland or other excitable tissue, or cause an augmenting action upon any function or metabolic process. [L. a goad]- adequate s. a s. to which a particular receptor responds effectively and that gives rise to a characteristic sensation; e.g., light and sound waves that stimulate, respectively, visual and auditory receptors.- aversive s. a noxious s. such as an electric shock used in aversive training or conditioning. SEE ALSO: aversive training.- conditioned s. 1. a s. applied to one of the sense organs ( e.g., receptors of vision, hearing, touch) which are an essential and integral part of the neural mechanism underlying a conditioned reflex; See classical conditioning, higher order conditioning. 2. a neutral s., when paired with the unconditioned s. in simultaneous presentation to an organism, capable of eliciting a given response.- discriminant s. a s. which can be differentiated from all other stimuli in the environment because it has been, and continues to serve as, an indicator of a potential reinforcer.- inadequate s. SYN: subthreshold s..- maximal s. a s. strong enough to evoke a maximal response.- square wave stimuli electrical stimulation in which the intensity of the current is brought suddenly to a given level and maintained at that level until it suddenly is cut off; this type of s. is particularly useful in obtaining a strength-duration curve.- subliminal s. SYN: subthreshold s..- supramaximal s. a s. having strength significantly above that required to activate all of the nerve or muscle fibers in contact with the electrode; used when response of all the fibers is desired.- threshold s. a s. of threshold strength, i.e., one just strong enough to excite. SEE ALSO: adequate s.. SYN: liminal s..- train-of-four s. a method for measuring magnitude and type of neuromuscular blockade, based upon the ratio of the amplitude of the fourth evoked mechanical response to the first one, when four supramaximal 2-Hz electrical currents are applied for 2 s to a peripheral motor nerve.- unconditioned s. a s. that elicits an unconditioned response; e.g., food is an unconditioned s. for salivation, which in turn is an unconditioned response in a hungry animal. See classical conditioning.
* * *1) STIMULANT (1)2) an agent (as an environmental change) that directly influences the activity of living protoplasm (as by exciting a sensory organ or evoking muscular contraction or glandular secretion) <a visual \stimulus>
* * *n. (pl. stimuli)any agent that provokes a response, or particular form of activity, in a cell, tissue, or other structure, which is said to be sensitive to that stimulus.
* * *stim·u·lus (stimґu-ləs) pl. stimґuli [L. â€œgoadâ€] any agent, act, or influence that produces functional or trophic reaction in a receptor or in an irritable tissue.
Medical dictionary. 2011.