[1 of 1] Swedenborg (1688-1772, Sweden): primary subject "Life, as changes of form" (search under Outer Life/Culture, Life, Society)": source "Spiritual Experiences, vol.4": detail "Section 4609 - 4610"
Perhaps some have an inward wish to know what mental images are, and where they come from. To tell it in a few words, they are not anything else but changes and variations in the inward substances that make up the inner person, thus the modifications and variegations there.
 When the life of the Lord flows into them, mental images are presented that are called thoughts. Those who do not comprehend that the inner qualities of human beings are real substances, and more real than their outward qualities, cannot conceive any sense of what mental imagery is.
 In the entire body nothing else constitutes life than the changes and variations of the forms in the substances there. Thus, for example, when a person speaks, then for every word or articulation of sound, there is a variation of the form of the glottis, trachea, and lungs, and of the throat, tongue, mouth, and area around the mouth. Countless such variations of form are presented within a moment there, even though in the body. This produces human speech. What may there not be in man's inward regions, where all things are more perfect, and thousands and tens of thousands of variations are happening in the time when only one thing is happening in the outward or bodily region?