The ideo-motor response (or "ideo-motor reflex"), often abbreviated to IMR, is a concept in hypnosis and psychological research. It is derived from the terms 'ideo' (idea, or mental representation) and 'motor' (muscular action). The phrase is most commonly used in reference to the process whereby a thought or mental image brings about a seemingly "reflexive" or automatic muscular reaction, often of minuscule degree, and potentially outside of the awareness of the subject.
The cognate term "ideo-dynamic response" (or "reflex") extends to the description of all bodily reactions caused in a similar manner by certain ideas, e.g., the salivation often caused by imagining sucking a lemon, which is a secretory response. Here, "ideo-dynamic" means "the power of an idea (over the body)". In the Victorian psychological terminology from which this concept derives, an "idea" may include any mental representation, e.g., a mental image or memory, etc.
The ideo-dynamic response became the original neuro-psychological theory of suggestion in hypnotism.
The term "ideo-motor reflex" or "ideo-motor response" was introduced in the 1840s by the eminent Victorian physiologist and psychologist William Benjamin Carpenter.
Carpenter was a friend and collaborator of James Braid.
James Braid (1795 –1860) was a Scottish physician and surgeon, specializing in eye and muscular conditions, Braid was an important and influential pioneer of hypnotism and hypnotherapy. Braid adopted the term "hypnotism" as an abbreviation for "neuro-hypnotism" or nervous sleep (that is, sleep of the nerves), in his lectures of 1841-2, and it is from his influential work that others derived the term "hypnosis" in the 1880s. Braid is regarded by many as the first genuine "hypnotherapist" and the "Father of Modern Hypnotism".
In The Physiology of Fascination (1855), Braid wrote:
“In order that I may do full justice to two esteemed friends, I beg to state, in connection with this term monoideo-dynamics, that, several years ago, Dr. W. B. Carpenter introduced the term ideo-motor to characterise the reflex or automatic muscular motions which arise merely from ideas associated with motion existing in the mind, without any conscious effort of volition. In 1853, in referring to this term, Dr. Noble said, “Ideo-dynamic would probably constitute a phraseology more appropriate, as applicable to a wider range of phenomena.” In this opinion I quite concurred, because I was well aware that an idea could arrest as well as excite motion automatically, not only in the muscles of voluntary motion, but also as regards the condition of every other function of the body. I have, therefore, adopted the term monoideo-dynamics, as still more comprehensive and characteristic as regards the true mental relations which subsist during all dynamic changes which take place, in every other function of the body, as well as in the muscles of voluntary motion."
 The ideo-motor reflex. Diagram from Carpenter's The Principles of Mental Physiology (1874).
 Daniel Noble (1810 - 1885) was a Catholic physician. A friend of surgeon James Braid and physiologist William Benjamin Carpenter, he is distinguished for his contributions to the study of mental illness and epidemic diseases.