Stimulation is the encouragement of development or the cause of activity in general. For example, "The press provides stimulation of political discourse." An interesting or fun activity can be described as "stimulating", regardless of its physical effects on senses. Stimulate means to act as a stimulus to; stimulus means something that rouses the recipient to activity; stimuli is the plural of stimulus.
A particular use of the term is physiological stimulation, which refers to sensory excitation, the action of various agents or forms of energy (stimuli) on receptors that generate impulses that travel through nerves to the brain (afferents). There are sensory receptors on or near the surface of the body, such as photoreceptors in the retina of the eye, hair cells in the cochlea of the ear, touch receptors in the skin and chemical receptors in the mouth and nasal cavity. There are also sensory receptors in the muscles, joints, digestive tract, and membranes around organs such as the brain, the abdominal cavity, the bladder and the prostate (providing one source of sexual stimulation). Stimulation to the external or internal senses may evoke involuntary activity or guide intentions in action. Such emotional or motivating stimulation typically is also experienced subjectively (enters awareness, is in consciousness). Perception can be regarded as conceptualised stimulation, used in reasoning and intending, for example. When bodily stimulation is perceived it is traditionally called a sensation, such as a kind of touch or a taste or smell, or a painful or pleasurable sensation. This can be thought of as psychological stimulation, which is a stimulus affecting a person's thinking or feeling processes.