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Efference copy

An efference copy, also referred to as an efferent copy or corollary discharge, is an internal neural signal that duplicates a motor command originating from the central nervous system, which is routed to sensory processing areas to anticipate and distinguish the sensory effects of self-initiated actions from those caused by external stimuli.^[1] This mechanism enables perceptual stability, such as maintaining a steady visual world during eye movements, by subtracting predicted sensory inputs from actual feedback.^[2] The concept of efference copy emerged in the mid-20th century from studies on motor-sensory integration. It was independently proposed by Roger Sperry in 1950, who described "corollary discharge" as a neural signal accompanying motor commands to predict sensory displacements, particularly in experiments involving visual inversion in animals.^[3] Concurrently, Erich von Holst and Horst Mittelstaedt formalized the "reafference principle" in 1950, introducing efference copy as a copy of efferent signals that interacts with incoming sensory (reafferent) signals to resolve perceptual ambiguities in self-motion.^[1] These ideas built on earlier observations by Hermann von Helmholtz in the 19th century, who noted discrepancies in perceived eye position during voluntary versus passive movements.^[2] In neural mechanisms, efference copies are generated in motor areas and transmitted via dedicated pathways to sensory cortices, where they modulate processing to suppress or adjust responses to expected self-generated sensations.^[4] For instance, in the oculomotor system, this signal provides extraretinal information about eye position, essential for accurate spatial perception and gaze control.^[5] Beyond vision, efference copies contribute to kinesthetic perception by encoding effort and intended limb trajectories, aiding in motor adaptation and error correction during tasks like reaching or balance maintenance.^[6] In auditory domains, such as speech production, they predict self-generated sounds to attenuate sensory feedback, preventing sensory overload and enabling fluent communication.^[4] Disruptions in efference copy signaling have been implicated in conditions like schizophrenia, where impaired distinction between self and external actions leads to anomalous perceptual experiences.^[1] Overall, this process underpins predictive coding in the brain, facilitating efficient interaction with the environment across species.^[7]

Fundamentals

Definition and Overview

An efference copy is an internal neural duplicate of an efferent motor command that is sent to relevant sensory systems to anticipate the sensory consequences of self-generated movements.^[8] This mechanism allows the brain to generate predictions about the sensory feedback resulting from motor actions, thereby facilitating efficient sensorimotor processing.^[9] The primary functions of efference copies include distinguishing self-produced sensory inputs from those caused by external stimuli, maintaining perceptual stability during active movements, and supporting the integration of sensory and motor information for adaptive behavior.^[1] By predicting expected sensory changes, efference copies help suppress or attenuate the processing of reafferent signals—those arising from one's own actions—preventing sensory overload and enabling accurate perception of the environment.^[8] Corollary discharge is a synonymous term often used interchangeably to describe this process.^[10] The concept of efference copy was introduced by Erich von Holst and Horst Mittelstaedt in 1950 in their seminal work on the reafference principle.^[10] For example, during voluntary eye movements, an efference copy predicts the shift in retinal images, allowing the visual system to compensate and keep the perceived world stable; in contrast, passive eye displacement (such as from external pressure) lacks this copy, resulting in illusory motion of the surroundings.^[1] Similarly, in proprioception, efference copies contribute to estimating limb position by forecasting changes based on motor commands, aiding in precise spatial awareness without relying solely on delayed sensory feedback.^[11]

Neural Mechanisms

Efference copies are generated primarily in the motor cortex, with additional contributions from subcortical structures such as the basal ganglia and cerebellum.^[12] In the basal ganglia, these copies are integrated into action selection circuits to update cortical representations of ongoing movements.^[13] The cerebellum receives efference copies via cortico-ponto-cerebellar pathways, enabling predictive adjustments to motor output based on internal models of limb dynamics.^[14] These generation sites ensure that copies are produced in parallel with primary efferent signals, facilitating rapid routing to sensory processing areas without disrupting the main motor pathway. Transmission of efference copies occurs through parallel neural pathways that branch from the motor command signals, which diverge to specific sensory and subcortical targets. For visual processing, copies are relayed to the superior colliculus via pathways from saccade-related motor layers, allowing anticipation of self-induced retinal slip.^[15] In the balance system, efference copies project to the vestibular nuclei, where they modulate primary vestibular afferents to distinguish self-motion from external perturbations.^[16] These parallel pathways maintain temporal alignment with the primary motor commands, typically involving axonal branching in the brainstem and thalamus to reach sensory cortices efficiently. The integration of efference copies involves forward models in areas such as the posterior parietal cortex, where predicted sensory consequences from the copy are subtracted from actual afferent inputs to compute perceptual errors.^[17] This process enables the suppression of self-generated sensory signals, with neurons in the parietal cortex dynamically updating spatial representations based on the mismatch.^[18] Key to this suppression involves inhibitory mechanisms to dampen reafferent activity in sensory pathways.^[19] Timing is critical, with efference copies exhibiting millisecond-scale delays that precisely match the latency of motor execution and sensory feedback loops.^[20]

Role in Motor Control

Efferent Motor Signals

Efferent motor signals represent the outgoing neural commands that initiate and coordinate voluntary and reflexive movements. These signals originate primarily from higher cortical regions, such as the primary motor cortex and supplementary motor area, where they encode intended actions through patterns of neural activity that drive alpha motor neurons in the spinal cord. Additionally, in rhythmic or locomotor behaviors, efferent signals arise from central pattern generators—networks of neurons in the brainstem and spinal cord that generate oscillatory motor outputs for actions like walking or swimming. An efference copy is created as a parallel duplicate of these commands, branching from the main efferent pathway to target sensory and associative brain areas, such as the cerebellum and parietal cortex, where it informs internal models of expected sensory outcomes.^[21]^[19] The efference copy plays a critical role in open-loop motor control, enabling the execution of initial movement phases without reliance on immediate sensory feedback. In this mode, the brain uses the copy to drive forward models that simulate the kinematic and dynamic consequences of the motor command, allowing rapid initiation of actions like ballistic reaches or startle reflexes where delays from sensory loops—typically 50-100 ms—would impair performance. This predictive mechanism reduces overall system latency by decoupling motor output from slow reafferent signals, ensuring smooth and timely execution in time-critical scenarios.^[22]^[23] Experimental evidence from deafferentation studies in animals underscores the sufficiency of efference copies for preserving movement prediction and execution. In rhesus monkeys subjected to bilateral dorsal rhizotomy, which severs sensory afferents from the forelimbs while leaving motor efferents intact, animals retained the ability to perform complex tasks like grasping and pointing with accuracy comparable to intact controls when visual guidance was available. These findings indicate that central efferent signals, via their copies, maintain an internal representation of limb state and trajectory, compensating for the absence of proprioceptive input and supporting predictive control. Similar results in cats with hindlimb deafferentation show preserved locomotor patterns driven by spinal efference copies from central pattern generators.^[24]^[25] In contrast to afferent feedback, which delivers reactive reafferent signals from peripheral sensors after movement onset to update and correct ongoing actions, efference copies provide proactive predictions derived directly from the motor plan. This distinction allows the nervous system to distinguish self-generated sensations from external stimuli in advance, minimizing perceptual disruptions during action. The efference copy thus forms the foundational signal for downstream processes like corollary discharge, which refines these predictions for sensory attenuation.^[1]

Corollary Discharge

Corollary discharge represents a key neural mechanism where a collateral copy of the motor command, originating from efferent signals, is transmitted to sensory processing regions to anticipate and adjust for the sensory repercussions of self-generated movements. This process facilitates forward modeling, allowing the brain to predict incoming sensory data rather than relying solely on afferent feedback. First articulated by von Holst and Mittelstaedt in their seminal 1950 work, the concept posits that the efference copy subtracts expected reafference from actual sensory input, thereby stabilizing perception and enabling efficient sensorimotor integration.^[10] In predictive modeling, corollary discharge enables the brain to simulate sensory outcomes prior to their occurrence, such as during rapid eye movements known as saccades. For instance, when the eyes shift to a new fixation point, the visual scene on the retina slips dramatically, but the brain uses the corollary discharge signal to forecast this displacement and maintain the illusion of a stable world. Electrophysiological recordings from primate brains reveal that neurons in the superior colliculus of the brainstem generate this signal, which propagates through the mediodorsal thalamus to the frontal eye fields in the cortex, with activity precisely timed to the onset and metrics of the saccade—typically peaking 10-20 milliseconds before movement execution. This pathway ensures that visual processing areas can remap receptive fields in advance, compensating for the impending retinal shift and preventing perceptual disruption.^[26] Beyond prediction, corollary discharge exerts a suppression function to dampen the impact of predictable self-generated sensory noise, thereby enhancing the salience of external stimuli. A prominent example occurs in the auditory domain during vocalization, where the signal attenuates neural responses in the auditory cortex to the speaker's own voice, reducing the N1 and P2 event-related potential components by up to 50% compared to externally presented sounds. This modulation, observed through magnetoencephalography in humans, aligns the suppression with the timing of phoneme production, allowing the brain to filter out predictable feedback while remaining sensitive to perturbations like echoes or alterations in pitch. Such attenuation prevents sensory overload and supports fluid communication by prioritizing unexpected auditory changes. Electrophysiological evidence underscores the temporal precision of corollary discharge signals across brainstem and cortical structures. Single-unit recordings in awake behaving primates demonstrate that burst-tonic neurons in the brainstem's superior colliculus exhibit perisaccadic modulation, firing in synchrony with motor commands to relay predictive information upstream. In the cortex, frontal eye field neurons integrate this input, showing enhanced or suppressed activity that correlates directly with saccade amplitude and direction, confirming the signal's role in aligning sensory expectations with motor execution. These findings, derived from chronic implants, highlight how corollary discharge operates on millisecond timescales to bridge motor output and sensory adaptation.

Historical Development

Early Concepts

The earliest conceptual foundations of efference copy emerged in the early 19th century through discussions of sensory-motor coordination, particularly in the context of visual perception during eye movements. In 1811, Johann Georg Steinbuch, in his work Beytrag zur Physiologie der Sinne, first articulated the puzzle of how the visual field remains stable despite active eye movements, suggesting the involvement of internal "outflow" signals from the motor system to anticipate and compensate for self-generated sensory changes.^[27] This idea highlighted the need for a mechanism to distinguish self-induced motion from external stimuli, though Steinbuch did not specify neural pathways.^[28] Building on such perceptual inquiries, Hermann von Helmholtz provided a more formalized theory in 1867 within his Handbuch der physiologischen Optik. He proposed the "outflow" (Efferenz) hypothesis, positing that a copy of the motor command signal for eye movements is sent centrally to the sensory areas, allowing the brain to predict and stabilize the perceived direction of visual objects despite shifts in retinal images.^[29] This concept explained why voluntary eye rotations do not cause disorientation, attributing spatial constancy to an internal efferent signal rather than purely afferent (inflow) feedback from eye muscles.^[30] Helmholtz's framework emphasized the role of these outflow signals in maintaining a coherent sense of visual direction, marking a pivotal shift toward integrating motor efference with sensory processing.^[31] In the early 20th century, Charles Sherrington advanced related ideas through his studies of neural integration, introducing the distinction between "efferent" (outgoing motor) and "afferent" (incoming sensory) pathways in reflex arcs. In his 1906 book The Integrative Action of the Nervous System, Sherrington described how efferent signals in spinal reflexes interact with central nervous mechanisms, implying potential internal feedback loops to coordinate motor output with sensory input, as seen in proprioceptive roles during eye movements.^[32] His work from the 1910s to 1930s, including observations on the proprioceptive supply of extraocular muscles, further hinted at efferent contributions to perceptual stability by modulating sensory responses in motor control circuits.^[27] These early concepts were limited by their pre-neural mapping era, relying on anatomical and philosophical reasoning to address perceptual puzzles like visual stability, without direct experimental validation of specific neural correlates or mechanisms. They laid essential groundwork but lacked the physiological detail that would emerge later.^[33]

Mid-20th Century Advances

In the mid-20th century, the concept of efference copy gained formal theoretical grounding through pioneering work on sensory-motor integration. Erich von Holst and Horst Mittelstaedt reintroduced the term "efference copy" in 1950 while studying compensatory head movements in insects, particularly during flight stabilization. They proposed the reafference principle, which posits that sensory feedback from self-generated movements (reafference) is distinguished from external sensory inputs (exafference) by subtracting a copy of the motor command (efference copy) from incoming signals, thereby maintaining perceptual stability despite ongoing motion.^[10] This framework explained how organisms predict and cancel self-induced sensory changes, resolving earlier ambiguities in reflex theory. Concurrently, Roger Sperry advanced the idea in 1950 by coining the term "corollary discharge" to describe a parallel neural signal accompanying motor commands, specifically in the context of eye movements in fish. In experiments involving visual inversion—where one eye was rotated 180 degrees—Sperry observed that fish exhibited spontaneous optokinetic circling movements, which persisted even after deafferentation of extraocular muscles, indicating a central neural mechanism that links efferent motor signals to expected sensory outcomes for behavioral adaptation.%20neural%20basis%20of%20the%20spontaneous%20optokinetic%20response%20produced%20by%20visual%20inversion.pdf) This corollary discharge effectively informed higher sensory centers of impending changes, preventing perceptual disruption and facilitating coordinated action. Hans-Lukas Teuber and his collaborators in the 1960s extended these principles to mammalian and human motor control, emphasizing interactions between efference copies and vestibular systems. Teuber's reviews highlighted how efference copies contribute to spatial perception and postural stability by modulating vestibular inputs during voluntary movements, integrating motor outflow with sensory feedback to achieve accurate environmental representation.^[27] Key empirical support came from vestibular deafferentation studies in the 1960s, which demonstrated efference-based compensation for lost sensory input. In labyrinthectomized animals, such as cats and monkeys, researchers observed rapid recovery of balance and locomotion through central recalibration, where ongoing motor commands generated predictive signals to substitute for absent vestibular reafference, underscoring the role of efference copies in adaptive motor function.^[34]

Applications in Adaptation

Sensory Compensation During Movement

Efference copies contribute to perceptual stability during self-initiated movements by enabling the brain to predict and compensate for the sensory consequences of those actions. In forward models of motor control, an efference copy of the motor command is used to simulate the expected sensory feedback, allowing the subtraction of self-generated sensory signals from the total afferent input. This predictive mechanism distinguishes self-motion from external perturbations, preventing illusions or disruptions in perception. For instance, when an individual moves, the forward model generates a prediction of the resulting sensory changes, such as shifts in visual or proprioceptive signals, which is then compared to actual sensory input to maintain a stable representation of the environment.^[35]^[36] One prominent example involves compensation for Coriolis forces during arm movements in rotating environments. When a person reaches while their body rotates, Coriolis forces deflect the arm perpendicular to its intended trajectory, creating illusory sensations of displacement. However, efference copies allow rapid adaptation by predicting these forces through an internal model, enabling corrective torques as demonstrated in experiments without visual or terminal tactile feedback. This adaptation occurs within a few trials, highlighting the efficiency of efference-based forward models in counteracting predictable inertial perturbations.^[37] In gaze stabilization, efference copies modulate the vestibulo-ocular reflex (VOR) to maintain visual fixation during head turns. The VOR generates compensatory eye movements to counteract head rotation, but its gain is significantly higher during active, self-generated head movements compared to passive ones, due to an efference copy signal that enhances predictive processing. This modulation ensures precise image stabilization on the retina, as neural responses in vestibular nuclei are adjusted based on the motor command for head motion, independent of vestibular sensory input alone. Electrophysiological recordings from primates confirm that central vestibular neurons exhibit reduced sensitivity to passive rotations but robust responses during voluntary movements, underscoring the role of efference in feedforward compensation.^[38]^[39] Experimental paradigms using prism goggles further illustrate efference-mediated recalibration. When prisms displace the visual field, initial reaching errors occur, but rapid adaptation ensues as efference copies update forward models to predict the shifted visual consequences of motor commands. Upon prism removal, an aftereffect reveals the recalibrated internal model, with reaches deviating in the opposite direction, confirming that adaptation involves predictive subtraction rather than mere sensory remapping. Neuro-computational models show that this process integrates efference copies with error signals to refine predictions, achieving near-complete compensation within 50-100 trials in healthy adults.^[40]^[41]

Force and Grip Adjustment

In precision grip tasks, efference copies facilitate load force coupling by enabling the motor system to scale grip forces in anticipation of an object's weight, ensuring stability during lifting without relying solely on delayed sensory feedback. This predictive mechanism operates with a lead time of approximately 100-150 ms, allowing grip adjustments to precede the actual load onset and maintain an adequate safety margin against slippage. For instance, when lifting objects of varying masses, the brain uses efference signals derived from motor commands to forecast the impending load force, resulting in coordinated increases in both grip and load forces that parallel each other closely.^[42]^[43] Research by Wolpert and colleagues has highlighted the role of efference copies in this predictive control during manipulation tasks, such as bimanual lifting where one hand generates load changes while the other restrains the object. In these experiments, participants modulated grip forces precisely to match predicted load dynamics, but only when sensory feedback from the load-producing hand was available, underscoring that efference copies alone require contextual sensory integration for optimal accuracy. This coupling demonstrates how internal forward models, informed by efference signals, allow for efficient, real-time adjustments in everyday object handling.^[36]^[44] Efference predictions are further refined through integration with tactile feedback for slip detection, where unexpected discrepancies between anticipated and actual sensations trigger force recalibration. Tactile afferents detect incipient slip via skin stretch or vibration, which, when combined with efferent-based predictions, enables corrective grip increases within milliseconds to prevent object loss. This hybrid process ensures robust control, as seen in tasks involving unpredictable loads, where sensory errors update the predictive model for subsequent trials.^[36] At the neural level, cerebellar forward models incorporate efference copies to compute these anticipatory grip adjustments, simulating the sensory outcomes of motor commands to guide force scaling. Functional imaging studies reveal heightened cerebellar activity during grip-load force coupling tasks at varying load levels, indicating its central role in generating precise predictions independent of force magnitude. These models allow the cerebellum to anticipate interaction dynamics, contributing to smooth and adaptive manipulation without excessive reliance on peripheral feedback.^[45]

Sensory Attenuation

Self-Generated Touch and Tickling

Efference copies enable the brain to predict the sensory consequences of self-generated movements, thereby attenuating the perception of predictable tactile stimuli to distinguish them from external touch. This mechanism suppresses neural responses in the somatosensory cortex, reducing the intensity of self-produced touch sensations compared to equivalent externally applied touch. Functional magnetic resonance imaging (fMRI) studies have demonstrated significantly reduced activation in the secondary somatosensory cortex (SII) during self-produced tactile stimulation versus external stimulation, with BOLD signal decreases observed bilaterally (p < 0.05, corrected).^[46] This predictive suppression significantly dampens somatosensory responses for predictable self-touch, prioritizing the detection of unexpected external inputs.^[47] A classic demonstration of this attenuation is the inability to self-tickle effectively, where self-generated tactile movements produce less ticklish sensation than identical movements performed by another person. In experiments by Blakemore and colleagues, participants rated self-produced tickle stimuli as less intense and ticklish than external ones (p < 0.001), with the difference attributed to precise spatiotemporal predictions from efference copies that cancel expected sensory feedback. When these predictions are disrupted—such as by introducing delays (100-300 ms) or trajectory rotations (30°-90°)—the attenuation decreases, and ticklishness increases proportionally (p < 0.0005 for delays; p < 0.01 for rotations). fMRI data from these studies further revealed lower activation in SII and the anterior cingulate cortex for self-tickling compared to external tickling, confirming that prediction mismatch enhances perceptual salience for non-self-generated touch.^[46]^[48]^[49] Beyond tickling, efference copy-mediated attenuation extends to broader self-generated tactile sensations, including cutaneous touch on the skin and proprioceptive feedback from limb movements. Self-touch feels less intense overall, with psychophysical measures showing reduced perceived pressure and vibration during voluntary actions compared to passive or external equivalents. This dampening occurs across somatosensory modalities, helping to filter redundant self-signals and enhance sensitivity to novel environmental interactions.^[47]^[50] The suppressive role of efference copies is confirmed by experiments dissociating motor commands from sensory feedback. When touch is generated by active voluntary movement (involving efference copy), somatosensory attenuation is robust, as evidenced by shifted point of subjective equality in intensity judgments (p < 0.001). In contrast, passive movement—lacking an efference copy—produces no significant attenuation (p = 0.799), rendering the sensation comparable to external touch and increasing perceived ticklability. These findings underscore that efference predictions, rather than reafference alone, drive the perceptual dampening of self-generated touch.^[47]

Auditory and Speech Feedback

Efference copy mechanisms significantly attenuate neural responses in the auditory cortex to self-generated sounds, such as one's own voice during speech production, enabling the brain to differentiate internal from external auditory inputs and prevent sensory flooding. In primates, single-unit recordings reveal widespread suppression of auditory neuronal firing rates during self-initiated vocalizations, with median reductions of approximately 77% in the primary auditory cortex, highlighting the conserved role of efference copy across species.^[51] Such attenuation is thought to arise from forward models that predict the sensory outcomes of motor commands, subtracting expected self-produced signals from incoming feedback to sharpen perception of environmental sounds. In speech motor control, efference copies facilitate precise predictions of vocal tract acoustics, supporting fluent articulation by minimizing interference from real-time auditory echoes. These predictions, derived from motor commands in frontal speech areas, are relayed to the auditory cortex to generate an internal model of expected sound output, allowing speakers to maintain rhythm and intonation without disruptive self-hearing.^[9] Disruptions in this process, such as when predictions mismatch actual acoustics due to vocal errors, result in reduced suppression and heightened sensitivity to deviations, prompting rapid motor corrections for ongoing speech. This mechanism parallels tactile self-touch attenuation but is specialized for the dynamic, time-sensitive demands of vocalization. Functional magnetic resonance imaging (fMRI) studies provide evidence for efference copy involvement in inner speech, where silent articulation activates predictive signals akin to overt production. A 2017 study demonstrated content-specific suppression of auditory responses during inner phoneme production (e.g., /ba/ matching an external stimulus), with reduced N1 event-related potential amplitudes indicating efference-mediated attenuation even without acoustic output.^[8] These findings suggest that covert speech engages similar forward modeling to prepare the auditory system, potentially aiding in subvocal planning and reducing cognitive load from imagined sounds. Perturbation experiments further illustrate efference copy's role in speech feedback processing, where mismatches between predicted and altered auditory input trigger compensatory responses. For instance, introducing delays or pitch shifts in real-time voice feedback (e.g., 100-200 ms delay or 100-cent upward shift) elicits automatic pitch adjustments in speakers, with response latencies around 150 ms reflecting error detection via efference comparison.^[52] These shifts scale with perturbation magnitude and habituate over repeated exposure, underscoring the adaptive nature of efference-based monitoring to maintain vocal accuracy amid environmental or internal variations.

Comparative and Pathological Aspects

Electric Fish and Other Animals

In mormyrid electric fish, such as Gnathonemys petersii, efference copies play a crucial role in the electrosensory system by suppressing self-generated signals from electric organ discharges (EODs) during active electrolocation, particularly when hunting prey. These fish emit brief EOD pulses to sense their environment via electroreception, but the resulting reafferent signals must be distinguished from external ones to avoid sensory overload. Efference copies, originating from command nuclei in the brainstem, target the electrosensory lateral line lobe (ELL), where they induce precise inhibitory responses in ampullary electroreceptor afferents, canceling predictable self-induced inputs within a narrow temporal window of 0–8 ms after the EOD command. This suppression enhances sensitivity to exogenous signals, such as those from nearby prey, allowing the fish to detect distortions in the electric field with high fidelity.^[53] Key studies by Christopher Bell demonstrated the modifiable nature of these efference copies in the ELL's nucleus region, where reafferent input can adapt the copy's strength over time through anti-Hebbian plasticity, forming a "negative image" of the expected sensory feedback. For instance, in curarized fish preparations, Bell showed that corollary discharges precisely time inhibitory postsynaptic potentials in ELL granule cells, aligning with EOD pulses to gate self-generated electrosensory noise while preserving communication signals during social interactions. This mechanism ensures that during hunting, the fish's electrosensory lobe focuses on environmental perturbations rather than its own emissions. In invertebrates, efference copies contribute to flight stabilization by predicting self-induced visual flow, as seen in Drosophila melanogaster. During rapid yaw turns in flight, motor-related signals—termed saccade-related potentials (SRPs)—conveyed via descending neurons reach visual processing neurons in the lobula plate, such as horizontal system (HSN) cells, approximately 30 ms before wingbeat changes. These SRPs have an opposite polarity to expected optic flow responses, suppressing the perception of self-generated motion and preventing reflexive optomotor turns that could destabilize flight. Recordings from visual interneurons reveal that SRPs hyperpolarize or depolarize cells to counteract reafferent visual input, maintaining stable gaze and course correction based on external cues. Similar processes occur in locusts, where corollary discharges recorded from the cervical connective suppress visual responses during saccades, reducing blur and aiding aerial navigation.^[54]^[55] The use of efference copies for self/non-self distinction in active sensing exhibits evolutionary conservation across taxa, from mormyrid fish to insects, underscoring a shared neural strategy to filter reafferent signals in diverse sensory modalities. In both groups, these copies target early sensory stages—electrosensory lobes in fish and optic flow detectors in insects—to enable precise environmental interaction without interference from self-motion. This conservation highlights the fundamental role of predictive motor signaling in adaptive behaviors, as initially evidenced in classic experiments on fish with visually inverted eyes, where mismatched efference copies induced disorientation.^[56]

Clinical Implications and Deficits

Disruptions in efference copy mechanisms have been implicated in various neurological and psychiatric disorders, particularly those involving impaired sensory prediction and agency attribution. In schizophrenia, hypoactive efference copy signals contribute to sensory overload and delusions of external control, as patients fail to adequately suppress self-generated sensory inputs, leading to an inability to distinguish internal actions from external influences.^[57] Functional MRI studies have provided evidence for this, showing reduced activation in cortical regions responsible for forward modeling during self-initiated movements, correlating with symptom severity including auditory hallucinations and passivity experiences.^[58] A 2025 neuroimaging analysis further demonstrated altered efference copy processing in schizophrenia, with diminished corollary discharge in auditory pathways exacerbating delusional ideation.^[59] Similar predictive deficits appear in autism spectrum disorders and related motor conditions, where impaired efference copy integration disrupts speech and movement planning. In autism, weakened efference signals hinder the brain's ability to anticipate sensory consequences of actions.^[60] Computational reviews of motor function in autism highlight how faulty forward models, reliant on efference copies, lead to imprecise kinesthetic predictions during self-generated movements, exacerbating coordination issues.^[61] Recent studies on individuals with heightened autistic traits confirm disrupted visuo-motor updating via efference copies, resulting in unstable perceptual stability and compensatory repetitive behaviors.^[62] Emerging research underscores the broader implications of efference copy in cognitive processes. A 2021 study proposed the efference copy as a core mechanism for consciousness, enabling the distinction between self-generated and external sensory events to form a coherent sense of agency and awareness.^[63] In theory of mind, efference copy-related predictive coding supports inferring others' intentions by simulating action outcomes, with 2023 frameworks linking agency models to self-awareness deficits in social cognition disorders.^[64] For obsessive-compulsive disorder (OCD), deficits in efference copies contribute to impaired agency and control in compulsive behaviors, as evidenced in embodied cognition models.^[65] Therapeutic interventions targeting efference copy enhancements show promise in motor disorders like Parkinson's disease. Neurofeedback training, which uses real-time EEG feedback to modulate brain activity, has been applied to improve motor adaptation, reducing bradykinesia and gait instability.^[66] In Parkinson's, where efference copy deficits impair stride length regulation and turning perception through mismatched kinaesthetic feedback, such training enhances sensory-motor compensation as per systematic reviews.^[67]^[68]

References

[1]
The Efference Copy Signal as a Key Mechanism for Consciousness
Nov 26, 2021 · This can be done by an efference copy mechanism, a carbon copy of the movement-command that is routed to sensory structures.
[2]
Efference Copy - an overview | ScienceDirect Topics
A term efferent copy (sometimes efference copy) was introduced by von Holst in 1954 to address hypothetical motor command signals that take part in perception.
[3]
[PDF] Sperry (1950) Neural basis of the spontaneous optokinetic response ...
Thus, any excitation pattern that normally results in a movement that will cause a displacement of the visual image on the retina may have a corollary discharge.
[4]
What Does Motor Efference Copy Represent? Evidence from ...
Oct 9, 2013 · Efference copy is thought to reflect the predicted sensation of self-produced motor acts, such as the auditory feedback heard while speaking.
[5]
A review of the role of efference copy in sensory and oculomotor ...
Efference copy is an internal copy of a motor innervation. In the oculomotor system it provides the only extraretinal signal about eye position that is ava.Missing: definition | Show results with:definition<|control11|><|separator|>
[6]
Efference copy in kinesthetic perception: a copy of what is it? - PMC
In this review, we consider definitions for efference copy, percept, and sense of effort based on recent studies within the physical approach.
[7]
Efference copies: Context matters when ignoring self-induced motion
Oct 25, 2021 · Across the animal kingdom, efference copies of neuronal motor commands are used to ensure our senses ignore stimuli generated by our own ...Missing: definition | Show results with:definition
[8]
Neurophysiological evidence of efference copies to inner speech
Dec 4, 2017 · Efference copies refer to internal duplicates of movement-producing neural signals. Their primary function is to predict, and often suppress ...
[9]
What Does Motor Efference Copy Represent? Evidence from ... - PMC
Oct 9, 2013 · Efference copy is thought to reflect the predicted sensation of self-produced motor acts, such as the auditory feedback heard while speaking.
[10]
Das Reafferenzprinzip | The Science of Nature
Das Reafferenzprinzip. Wechselwirkungen zwischen Zentralnervensystem und Peripherie. Aufsätze; Published: January 1950. Volume 37, pages 464–476, ...
[11]
Contributions of Efference Copy to Limb Localization
We propose that efference copy can provide a consistent estimate of limb position that becomes less informative over the course of the movement. We discuss the ...
[12]
The efference cascade, consciousness, and its self - Frontiers
Implemented through a staggered cortical “efference cascade” originating in the descending axons of layer five pyramidal cells throughout the neocortical ...
[13]
Basal ganglia reign through downstream control of motor centers in ...
May 19, 2021 · Basal ganglia reign through downstream control of motor centers in midbrain and brain stem while updating cortex with efference copy information.
[14]
Mechanisms of human cerebellar dysmetria: experimental evidence ...
Apr 13, 2009 · The cortico-ponto-cerebellar tracts bring an efference copy of a motor command to the cerebellar cortex. The cerebellum would compute an ...
[15]
Pathways from the superior colliculus and the nucleus of the optic ...
May 24, 2025 · MSTl is the target of efference copy pathways from saccade‐ and head‐related compartments of SC motor layers and head‐related reticulospinal ...
[16]
Role of locomotor efference copy in vertebrate gaze stabilization
Dec 9, 2022 · Efference copies (ECs) of the spinal motor program that generates axial- or limb-based propulsion directly drive compensatory eye movements.
[17]
Forward Prediction in the Posterior Parietal Cortex and Dynamic ...
Oct 26, 2016 · As a crucial node incorporating visual, proprioceptive and efference copy information in a sensorimotor network (Andersen et al., 1997), the ...
[18]
Forward estimation of movement state in posterior parietal cortex
Inputs to PPC consist of visual and proprioceptive sensory signals and, potentially, an efference copy signal. Plausible PPC outputs to be tested are (i) the ...
[19]
Role of locomotor efference copy in vertebrate gaze stabilization
Dec 8, 2022 · Accordingly, locomotor ECs could activate GABAergic interneurons that cause both a postsynaptic inhibition of central neurons and a ...
[20]
The Forward Model: A Unifying Theory for the Role of the ... - Frontiers
The cerebellum is thought to integrate the efference copy—a copy of the motor command that originates from the motor and premotor areas and represents the ...Introduction · Functional Neuroanatomy of... · The Cerebellum as A Predictor...
[21]
Supplementary motor area provides an efferent signal for sensory ...
An efference copy of the motor command sent to the muscles may be used by an internal predictive model to predict the sensory consequences of the command. The ...Missing: branching | Show results with:branching
[22]
Internal Models in Biological Control - PMC - NIH
Internal models are predictive models of the world and actions, allowing organisms to try alternatives and react to future situations.
[23]
Motor Behavior Following Deafferentation in the Developing and ...
Following deafferentation of both forelimbs by dorsal rhizotomy, motorically mature rhesus monkeys are able to make extensive use of the affected ...
[24]
Deafferentation in monkeys: pointing at a target without ... - PubMed
Deafferentation in monkeys: pointing at a target without visual feedback. Exp Neurol. 1975 Jan;46(1):178-86. doi: 10.1016/0014-4886(75)90040-0. Authors. E Taub ...Missing: efference copy control
[25]
Saccadic Corollary Discharge Underlies Stable Visual Perception
Jan 6, 2016 · We conclude that this corollary discharge provides a critical signal that can be used to unite jumping retinal images into a consistent visual scene.
[26]
Early concepts on efference copy and reafference
Feb 4, 2010 · Early concepts on efference copy and reafference. Published online by Cambridge University Press: 04 February 2010. Otto-Joachim Grüsser.
[27]
Active sensing without efference copy: referent control of perception
EC is a central concept in the “reafference principle” proposed by von Holst (von Holst and Mittelstaedt 1950; von Holst 1954) to explain how posture and ...Missing: original | Show results with:original
[28]
Multiple sources of outflow in processing spatial information
The role of outflow (efference copy) is investigated by pressing on the eye while maintaining visual fixation, so that outflow is biased while image ...
[29]
Gaze-Centered Remapping of Remembered Visual Space
Nineteenth century investigators recognized that this “space constancy” problem could only be solved if the brain somehow takes eye movement into account, ...
[30]
Perceptual Stability—Going with the Flow - Sage Journals
Jan 1, 2008 · Historically, inflow and outflow hypotheses have been formulated as the primary explanations for perceptual stability.
[31]
Charles Scott Sherrington's Integrative Action: a centenary notice
In the reflex arc, the 'wiring diagram' of the spinal reflexes, afferent (sensory) and efferent (motor) elements were related at centres in the grey matter ...
[32]
On the history of the ideas of efference copy and reafference - PubMed
On the history of the ideas of efference copy and reafference. Clio Med. 1995:33:35-55. Author. O J Grüsser. Affiliation. 1 Physiologisches Institut der ...Missing: early Steinbuch Helmholtz Sherrington
[33]
[PDF] General Disclaimer One or more of the Following Statements may ...
Holst, von, E., and Mittelstaedt, H., 1950, "Das Reafferenzprinzip (Wechsel- wirkungen zwischen Zentralnervensystem and Peripherie)", Naturwissenschaften. 37 ...
[34]
[PDF] Primer - Sensorimotor Learning Group (Wolpert-lab)
forward models that predict the behaviour of the motor systems when interacting ... efference copy of the motor command is used to simulate the sensory ...<|separator|>
[35]
Predicting the Consequences of Our Own Actions
Sep 15, 1998 · Such models are known as forward models because they capture the forward or causal relationship between actions, as signaled by efference copy ( ...
[36]
Rapid adaptation to Coriolis force perturbations of arm trajectory
Forward reaching movements made during body rotation generate tangential Coriolis forces that are proportional to the cross product of the angular velocity ...Missing: efference copy
[37]
Vestibuloocular reflex signal modulation during voluntary ... - PubMed
The vestibuloocular reflex (VOR) effectively stabilizes the visual world on the retina over the wide range of head movements generated during daily ...
[38]
Vestibuloocular Reflex Signal Modulation During Voluntary and ...
The vestibuloocular reflex (VOR) effectively stabilizes the visual world on the retina over the wide range of head movements generated during daily ...
[39]
Towards a neuro-computational account of prism adaptation - PMC
An efference copy of this motor command is sent to visual (5a) and proprioceptive (5b) forward models that generate modality-specific predictions about the ...
[40]
Prism Adaptation of Reaching Movements: Specificity for the ...
Feb 15, 1997 · A proprioceptive shift is most likely to alter the in-flight corrections of movements that use the efference copy of motor commands and the ...Missing: goggles | Show results with:goggles
[41]
Programmed and triggered actions to rapid load changes ... - PubMed
These actions appeared ca. 150 ms prior to the impact and involved a grip force increase and a lifting movement of the grip apparatus. The e.m.g. activity ...Missing: coupling predictive 100-150
[42]
Adjustments of prehension synergies in response to self-triggered ...
In particular, two recent studies documented changes in indices of multi-digit synergies stabilizing the total force generated by a set of digits 100–150 ms ...
[43]
How predictive is grip force control in the complete absence of ...
The predicted sensory consequences of a movement may be generated using the internal model in conjunction with a copy of the motor command (efference copy).
[44]
Internal forward models in the cerebellum: fMRI study on grip force ...
Forward internal models predict sensory consequences from efference copies of motor commands. There is growing acceptance of the idea that forward models are ...Missing: anticipatory adjustments
[45]
Central cancellation of self-produced tickle sensation - PubMed
A self-produced tactile stimulus is perceived as less ticklish than the same stimulus generated externally.Missing: efference copy
[46]
Efference Copy Is Necessary for the Attenuation of Self-Generated ...
Feb 21, 2020 · Self-generated touch feels less intense than external touch of the same intensity. According to theory, this is because the brain predicts and ...
[47]
[PDF] Spatio-Temporal Prediction Modulates the Perception of Self ...
It has been argued that efference copy produced in parallel with the motor command underlies this phenomenon. In Weiskrantz et al.'s (1971) psychophysical study ...
[48]
[PDF] Why can't you tickle yourself? - Stanford University
An efference copy of the motor command. [8] is used to generate continuously predictions of the sensory consequences (or corollary discharge [9]) of the ongoing ...
[49]
Attenuation of Somatosensory Responses to Self-Produced Tactile ...
Jun 8, 2009 · The very early start of the attenuation already about 30 ms after stimulation onset is in line with the hypothesis of forward mechanisms, based ...
[50]
Sensory-Motor Interaction in the Primate Auditory Cortex During Self-Initiated Vocalizations | Journal of Neurophysiology | American Physiological Society
### Summary of Findings on Suppression of Auditory Responses During Self-Initiated Vocalizations in Primate Auditory Cortex
[51]
Time-dependent Neural Processing of Auditory Feedback during ...
The 10-dB gain between the voice and the feedback channels allowed the recording of ERPs in response to pitch-shifted auditory feedback by partially masking the ...
[52]
https://pmc.ncbi.nlm.nih.gov/articles/PMC3268676/
[53]
https://doi.org/10.1126/science.7291985
[54]
Cellular evidence for efference copy in Drosophila visuomotor ...
Classic behavioral experiments suggested that flies use active neural-circuit mechanisms to suppress the perception of self-generated visual motion during ...
[55]
https://pmc.ncbi.nlm.nih.gov/articles/PMC6327952/
[56]
Computational models of the “active self” and its disturbances in ...
Growing evidence supports the notion of schizophrenia as a self-disorder stemming from a system-level disturbance of the bodily active self.
[57]
Predictive neural processing of self-generated hand and tool actions ...
Mar 17, 2025 · In this study, we investigated the neural correlates and potential dysfunctions of action feedback processing in SSD during tool use actions and bimodal ...
[58]
Auditory efferent suppression during alternate auditory attention in ...
Mar 20, 2025 · Cortical network disruption is minimal in early stages of psychosis. Schizophrenia Bull. Open. 5 https://doi.org/10.1093/schizbullopen/sgae010 ( ...
[59]
The Hypothesis of Apraxia of Speech in Children with Autism ... - NIH
The core feature of both congenital and acquired apraxia of speech is a deficit in the planning/programming processes that transcode linguistic representations ...
[60]
[PDF] Motor Abilities in Autism: A Review Using a Computational Context
A copy of the motor command (efference copy) is sent to a forward model, which rapidly generates a prediction of the sensory con- sequences of the action ( ...<|separator|>
[61]
Visuo-motor updating in individuals with heightened autistic traits
Feb 13, 2024 · Here, we examine the idea that sensory overload in ASD may be linked to issues with efference copy mechanisms, which predict the sensory ...
[62]
The Efference Copy Signal as a Key Mechanism for Consciousness
Nov 25, 2021 · This can be done by an efference copy mechanism, a carbon copy of the movement-command that is routed to sensory structures.Missing: loop latency
[63]
The cognitive neuroscience of self‐awareness: Current framework ...
Dec 3, 2023 · Models of agency typically rely on the concept of efference copy, which has its roots in corollary discharge theory (Feinberg, 1978).
[64]
Obsessive-Compulsive Disorder from an Embodied Cognition ...
The efference copy or corollary discharge is the reproduction of the ideal state of action by structures that manage sensory and motor processes (52). The ...
[65]
A Systematic Review of Neurofeedback for the ... - PubMed Central
Sep 29, 2021 · Background: Neurofeedback has been proposed as a treatment for Parkinson's disease (PD) motor symptoms by changing the neural network ...Missing: efference | Show results with:efference
[66]
Stride length regulation in Parkinson's disease: the use of extrinsic ...
In this model, the reduced kinaesthetic feedback arising from the reduced movement amplitude matches the underscaled efference copy, resulting in the regulation ...
[67]
Perception of Active and Passive Turning in Parkinson Disease
This fusion of vestibular, proprioceptive, and efference copy cues may improve accuracy of active self-turning com- pared to passive turning. Deficits in fusion ...<|separator|>