|This article does not cite any references or sources. (February 2008)|
Stimulation is the action of various agents (stimuli) on nerves, muscles, or a sensory end organ, by which activity is evoked; especially, the nervous impulse produced by various agents on nerves, or a sensory end organ, by which the part connected with the nerve is thrown into a state of activity.
The word is also often used metaphorically. For example, an interesting or fun activity can be described as "stimulating", regardless of its physical effects on nerves.
(Note)Stimulate means act as stimulus to, stimulus means things that rouses to activity, now rouses means exciting, stirring.
Stimulation in general refers to how organisms perceive incoming stimuli. As such it is part of the stimulus-response mechanism. Simple organisms broadly react in three ways to stimulation: too little stimulation causes them to stagnate, too much to die from stress or inability to adapt, and a medium amount causes them to adapt and grow as they overcome it. Similar categories or effects are noted with psychological stress with people. Thus, stimulation may be described as how external events provoke a response by an individual in the attempt to cope.
Psychologically, it is possible to become habituated to a degree of stimulation, and then find it uncomfortable to have significantly more or less. Thus one can become used to an intense life, or television, and suffer withdrawal when they are removed, from lack of stimulation, and it is possible to also be unhappy and stressed due to additional abnormal stimulation.
It is hypothesized and commonly believed by some that psychological habituation to a high level of stimulation ("over-stimulation") can lead to psychological problems. For example, some food additives are hypothesized to cause children to become prone to over-stimulation, and ADHD is, theoretically, a condition in which over-stimulation is a part. However, ADHD is believed to be a heterogeneous disorder with genetic, environmental and psychosocial causes among which food additives may the part. It is also hypothesized that long term over-stimulation can result eventually in a phenomenon called "adrenal exhaustion" over time, but this is neither medically accepted nor proven at this time.