Stimulation

Stimulation is the irritating action of various agents (stimuli) on muscles, nerves, 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.

Overview
Stimulation in general refers to how organisms perceive incoming stimuli. As such it is part of the stimulus-response mechanism. It is well known that simple organisms broadly react 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 effect are noticed 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.

Over-stimulation
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 can result in children becoming prone to over-stimulation, and ADHD is a condition inwhich over-stimulation is a part. It is also hypothesized that long term over stimulation can result eventually in a phenomenon called "adrenal exhaustion" over time, but this is not medically accepted or proven at this time.

What is sure is that ongoing, long term stimulation, can for some individuals prove harmful, and a more relaxed and less stimulated life may be beneficial.