Efference copy

The Reafferenzprinzip is a model in the field of motion control - the motions of living organisms. It represents a control principle, which allows the central nervous system, hide expected stimuli. Because of this principle can be explained as to why in the environment of the eye movement is perceived as being rigid, while the movements of the environmental map to the retina.

The Reafferenzprinzip was approximately in the middle of the 20th century discovered by Erich von Holst, named and described and published in his eponymous essay in the journal Science first.

Description

The basic idea of ​​Reafferenzprinzips is that of the commands ( efferent ) to the execution systems ( for example, the muscles) in the lowest, but still central center of the nervous system (Z1 ) a copy is saved ( efference, EK ) ( ) is. The commands are then sent to the effectors (EFF) passed (E) and executed there. Of the effectors ( reafferences ) and the environment ( Exafferenzen ) are messages of the type ( A, - ) re- routed to the central bottom center and offset against the stored efference. Are efference and feedback the same - so there is no residual - the process is complete. But there is a remainder, this is reported to the next higher central center and an attempt is from there, triggered by new commands, the new reafferences and Exafferenzen to remove the remains of the efference copy. Failing that, the next higher center will endeavor (M). This process is carried out until the efference copy is deleted. Where the " error message" to the highest center in the cortex (Zn ), the operation of the necessary correction is aware.

An important implication of the Reafferenzprinzip is that the organism between signals, which are caused by its own movement can differ ( proprioceptive signals) and the signals coming from the environment as Exafferenzen.

Von Holst describes in his article also how (for example, space or size constancy ) let in psychology ( Gestalt and cognitive psychology ) significant constancy phenomena explained with the help of Reafferenzprinzips.

Example ( reported by von Holst in his article on the Reafferenzprinzip ): from centipede is known that then, if you give them a half of her brain removed, creeping around in regular circles according to the intact side. If you then from the back part of her body cut them some segments, the circles are close, the narrower the more segments were cut off. This can be explained with the Reafferenzprinzip. Because the efferent signals for the "normal " circuit are stored in the efference copy. The feedback on the actual movement but can only come from the segments that still remain. Therefore remain remnants of the efference copy. In order to ensure that these are deleted, the worm the existing segments must contract until he has completed the efference feedback. This means that the worm crawling in a narrow circle.

General version

It is generally spoken of centers:

Of the efference E for a sequence of movements, which emanates from a parent Zn nervous center in a given sub- centers EK efference copy is created.

In interaction with this and the reafference A of the effector EFF, we take a movement success true. This allows movement sequences that are influenced by the other parent centers or from the outside, can be controlled and regulated.

The efference copy is the target state, the position of the end effector of the actual state, a difference between the two Exafferenz M.

Formation and development of the theory of Reafferenzprinzips

Reflexes, Refelxketten, reflexology

In the early 20th century began the scientific study of the nervous system. Two of the most outstanding researchers were Charles Scott Sherrington (1857-1952) and Ivan Petrovich Pavlov ( 1849-1936 ). Both dealt with the Reflexen.Während but Sherrington mainly the anatomy of individual nerve cells and examined their function, Pavlov developed important models of the reflexes ( stimulus-response theory).

Sherrington, for example, discovered that the nervous system is no coherent structure ( syncytium ) that it consists rather of individual neurons, which are physiologically separated from each other, but can exchange signals with each other at certain points.

Pavlov developed, among others, the theory of the conditioned reflex (see Pavlov's dog), which was also the basis of behaviorism. Together with Vladimir Mikhailovich Bekhterev (1857-1927) he developed the mechanistically oriented psychology. From this, the behavior described as a series of reflections ( stimulus reaction scheme: The reaction (muscle contraction) to a stimulus, the triggering stimulus ( stimulus) to the next muscle contraction ). More complex, differentiated (for example, instinctive ) behaviors are learned from them as a reflex chains and as bases behavior ( see learning theories - Conditioning ) is considered. This reflex chains formed a very rigid system - imagine like a slot machine - are triggered and performed by the movements. The individual elements of complex movements are then completely dependent of each other. ( This theory is referred to as reflexology ).

It was imagined long time that by such reflex chains complex movements arise and would also be controlled, for example, the creep of a worm or the beating of the wings of a bird. Also on the movement of people put you up ( in behaviorism ) states that it comes into being in this way.

Development of Reafferenzprinzips

However, there were also doubts about this very rigid interpretation of the movement formation and control, because in many animals by disturbances in their normal mode of locomotion were also others, but quite controlled movements. One of the researchers who had looked into these phenomena German physiologist Erich von Holst (1908-1962), who did his doctorate in 1932 on the function of the central nervous system in the earthworm. He observed in his studies of locomotion of living organisms - worms, fish, flies, and others - that their limbs ( for example, the fins) did not move very smoothly in the same cycle but sometimes completely independent of each other. He described the latter as opposed to the uniform motion ( absolute coordination) and relative coordination. After further systematic studies and reflections on these phenomena, he developed the model of the Reafferenzprinzips.

He was aware, however, that this model into which at the time evolving consciousness of biologists and physiologists fit that play in the functioning of living beings numerous regulatory processes in the organism. He mentioned only incidentally, possibly because it is not a simple feedback but a feedforward system in which Reafferenzprinzip. They have not been often described, at the time.

Slow dissemination

1950 his ideas in the essay will be published in the journal The Reafferenzprinzip natural sciences, which he co-authored with Horst Mittelstaedt. Four years later an English summary of it on the Reafferenzprinzip in the British Journal of Animal Behaviour appears.

The Reafferenzprinzip is indeed occasionally mentioned in the following years in the context of the control loops in the body for the movements ( for example, in Volume 14 of the sensorimotor series Human Physiology, published in 1976 by OH Gauer, K.Kramer and R.Jung ). Its full significance was not recognized for a long time. In the English / American debate on the motor activity of the human Reafferenzprinzip long time hardly played a role - there was no complete translation and it was so little known. Often it was equated discharge with the similar concept of the corollary.

It was only in the 80s of last century, when the importance of motor skills research grew and became more internationally worked together, some work on the Reafferenzprinzip could find. For example, in Charles Gallistel 1980. Heidrun Schewe also described the Reafferenzprinzip and its importance to the movement and motor learning in 1988 in her book The movement of people. But especially around the turn of the millennium, when even mathematicians involved more because of Reafferenzprinzips reached new meaning.

Neuroscience and Reafferenzprinzip

Also, the neuroscience had developed and it was known that there are different types of control of processes in living organisms. Especially Daniel M. Wolpert ( motor researcher and mathematician, Cambridge, England ) and his group is concerned with the verification of Holst's ideas and its further exploration. He had, for example, 1995 shown in an article that can be described with the operation of a Kalman filter, the Reafferenzprinzip. From this he developed the idea that also arises from Holt's description that the organism several control centers are available. First work in this idea a forward ( forward: it determines and controls from the current state and the motor commands to the next state ) and a backward ( inverse: it supplies the motor command that causes the desired change ) Control together to movements optimally to control. Furthermore, it is assumed that there are a variety of such signal pairs in the organism. This leads to a modular design of the motion control and has great significance for motor learning.

The ability to distinguish between proprioceptive and exafferenten signals can lead to the self-perception is attenuated. This coming signals can be perceived precisely as needed from the outside.

Other examples

The concept of efference copy is also to explain other effects:

• It is most people are not able to tickle themselves because the body awaits the touch of one's hand.
• Animals with active sensors (such as the echolocation of bats ) have the problem that their sensors can actually perceive only their own signal when sending. By Reafferenzprinzip but it is possible, the expected response of the sensors of the efference copy " subtract " and so perceive only the actual response of the environment. Curtis Bell showed this 1982 very impressive on the electrical perception of the elephant trunk fish.
• Can crickets singing their own neuronal " Hide " from our own perception.