The corollary discharge theory (CD) of motion perception helps understand how the brain can detect motion through the visual system, even though the body is not moving. When a signal is sent from the motor cortex of the brain to the eye muscles, a copy of that signal (see

efference copy In physiology, an efference copy or efferent copy is an internal copy of an outflowing ('' efferent''), movement-producing signal generated by an organism's motor system.Jeannerod, Marc (2003): "Action Monitoring and Forward Control of Movement". I ...

) is sent through the brain as well. The brain does this in order to distinguish real movements in the visual world from our own body and eye movement. The original signal and copy signal are then believed to be compared somewhere in the brain. Such a structure has not yet been identified, but it is believed to be the

Medial Superior Temporal Area The medial superior temporal (MST) area is a part of the cerebral cortex, which lies in the dorsal stream of the visual area of the primate brain. The MST receives most of its inputs from the middle temporal (MT) area, which is involved primarily in ...

(MST). The original signal and copy need to be compared in order to determine if the change in vision was caused by eye movement or movement in the world. If the two signals cancel then no motion is perceived, but if they do not cancel then the residual signal is perceived as motion in the real world. Without a corollary discharge signal, the world would seem to spin around every time the eyes moved. It is important to note that corollary discharge and efference copy are sometimes used synonymously, they were originally coined for much different applications, with corollary discharge being used in a much broader sense. __TOC__

Discovery

The first scientific research study looking at corollary discharge was done by Descartes in 1664 when he published his book the ''Treatise of Man''. He was studying apparent motion and developed early theories in an error of the mind to account for efferent signals centuries before corollary discharge theories developed. In his experiment he would take his finger and press it on the side of his eye. In doing this he would move the image across his retina. A signal was then sent to the brain saying that the image had moved and because there was no efference copy signal sent as well, his brain perceived motion. The term corollary discharge was finally coined in 1950 by Roger Sperry while doing studies on fish.

Physiology

When trying to map out how corollary discharge works in the brain, it is important to begin with the

superior colliculus In neuroanatomy, the superior colliculus () is a structure lying on the tectum, roof of the mammalian midbrain. In non-mammalian vertebrates, the Homology (biology), homologous structure is known as the optic tectum or optic lobe. The adjective f ...

. It is responsible for receiving visual signals from the

retina The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...

. In studies done on primate brains, a corollary discharge pathway has been found to begin in the superior colliculus. After receiving current information about the

visual field The visual field is "that portion of space in which objects are visible at the same moment during steady fixation of the gaze in one direction"; in ophthalmology and neurology the emphasis is mostly on the structure inside the visual field and it i ...

, a corollary discharge signal is sent from the superior colliculus to the

frontal eye field The frontal eye fields (FEF) are a region located in the frontal cortex, more specifically in Brodmann area 8 or BA8, of the primate brain. In humans, it can be more accurately said to lie in a region around the intersection of the middle fronta ...

, via the medial dorsal nucleus of the thalamus. The frontal eye field plays a very important role when it comes to eye movements. Particularly the frontal eye field is responsible for much of the

saccadic In vision science, a saccade ( ; ; ) is a quick, simultaneous movement of both eyes between two or more phases of focal points in the same direction. In contrast, in smooth-pursuit movements, the eyes move smoothly instead of in jumps. Control ...

eye movements that eyes make. Once the frontal eye field is activated by the corollary discharge signal, it sends a predictive signal to the

occipital lobe The occipital lobe is one of the four Lobes of the brain, major lobes of the cerebral cortex in the brain of mammals. The name derives from its position at the back of the head, from the Latin , 'behind', and , 'head'. The occipital lobe is the ...

. This signal essentially predicts what the visual field should look like after an eye movement. A signal is sent back from the occipital lobe to the frontal eye field describing actual visual input. In summary, the corollary discharge pathway is responsible for helping guide eye movements as well as keeping stable visual perception. Recent studies suggest that deficiencies within this pathway could be responsible for difficulties that schizophrenic patients have with controlling their own movements.

References

{{Reflist Visual perception