Your brain performs a constant act of self-recognition. Every time you move, speak, or shift your eyes, it generates an internal signal to tell itself, “I did that.” This process, known as corollary discharge, allows your brain to distinguish your own actions from information coming from the outside world. This internal system builds the boundary between “me” and “not me,” shaping your stable perception of reality.
How Your Brain Knows It’s You
Whenever the motor cortex initiates a command to move a muscle, it also sends an identical copy of that command, called an efference copy, to the sensory regions of the brain. This copy acts as a predictive message, informing these sensory areas what sensations to expect from the impending movement.
This mechanism allows the brain to sort sensory information. Sensations caused by our own movements are called sensory reafference, while those from external sources are known as exafference. The efference copy provides a template of the expected reafference, which is compared to the actual sensation when it arrives.
If the incoming sensation matches the prediction, the brain dampens or cancels it, recognizing it as self-generated. Any remaining sensory information is interpreted as coming from the external environment. This process filters out the sensory noise of your own body so you can focus on the world.
Keeping Your World Stable
A primary function of corollary discharge is maintaining perceptual stability. Your eyes, for instance, are in near-constant motion, performing rapid shifts called saccades. Each saccade causes the image on your retina to jump, yet you perceive the world as still because a corollary discharge signal is sent to the visual system before each eye movement.
This signal tells the visual cortex to expect a massive shift in input and to disregard it, a phenomenon known as saccadic suppression. Without this predictive signal, the world would appear to lurch and blur every time you shifted your gaze. The corollary discharge compensates for the retinal motion, allowing a stable visual experience.
Corollary Discharge in Daily Life
The effects of corollary discharge are evident in common experiences, such as the inability to tickle yourself. When you try to tickle your own foot, your brain generates a corollary discharge that predicts the sensation’s timing and location. This prediction cancels much of the sensory feedback, which is why the feeling is less intense than when someone else does it unexpectedly.
The same principle applies to how you perceive your own voice. As you speak, your brain sends a corollary discharge from the motor speech areas to the auditory cortex. This signal prepares the auditory system for the incoming sounds and dampens its response. This allows you to remain sensitive to external sounds while talking and recognize the voice as your own.
When Self-Monitoring Goes Awry
When the corollary discharge system malfunctions, the brain’s ability to distinguish self from other can break down. This dysfunction is a factor in some symptoms of schizophrenia. If the mechanism fails to signal that inner speech is self-generated, the brain may misattribute these thoughts to an external source, resulting in auditory hallucinations where a person hears their own thoughts as another voice.
This impairment can also explain delusions of control. If the brain does not receive the predictive signal that it is initiating an action, the movement can feel alien, as if controlled by an outside force. The sense of agency is disrupted because the comparison between the intended action and the sensory feedback fails.
Studies show that individuals with schizophrenia may be more successful at tickling themselves than the general population. Because their brain does not correctly predict and cancel the self-produced sensation, the tickle feels more like it is coming from an external source. This altered sensory experience reflects an issue in the neural circuits that integrate actions with perceptions.