We have all asked ourselves that enigmatical question: “Why can’t we tickle ourselves?” Actually, its answer is both simple and complex and it is lying in a fascinating brain mechanism, which is called corollary discharge, also it is known as the efference copy.
So, what exactly does this mechanism do? In this event, whenever we move or speak, our brains send a copy for the motor command to sensory areas to cancel sensory re-afferent generated by self-motion, and effectively whispering: “Don’t be surprised, this sensation is coming from you.” In more concrete words, this interesting mechanism allows us to distinguish between what our movements cause and what the outside world causes. But... What if this mechanism deteriorates? This is the unexpected door that opens to the schizophrenic minds.
According to some considerable studies, the measured brain responses while participants spoke simple vowel letters and then listened to recordings of their own speech showed that their brains reduced auditory responses when speaking compared to listening. Consequently, in healthy individuals, it is understood that corollary discharge helps the auditory system dampen responses to their own voice. However, strikingly; patients with schizophrenia did not show this response and subsequently, this demonstrate that their brains failed to label self-generated speech as “self-made”. Even it is argued that this deficit can be represented as a fundamental dysfunction in schizophrenia because the schizophrenic brain cannot mark the internal actions and thoughts as self-generated, the door opens to unwanted experiences, such as hearing some voices that feels alien, or believing their actions are controlled by others. Therefore, this situation proves that corollary discharge is very important in terms of maintaining the boundary between us and our external world.
As final words, from our inability to tickle ourselves to the devastating symptoms of auditory hallucinations, corollary discharge reveals that how important the sensitivity adjustments of the brain’s feedback mechanism to separate the inner from the outer and the self-perception from the real world. Besides, this function also opens a controversial window into schizophrenia with showing how a subtle failure in this neural processing can cause an profound problem in defining what it means to be “me”.
References
1. Poletti, M., Gebhardt, E., & Raballo, A. (2017). Corollary Discharge, Self-agency, and the Neurodevelopment of the Psychotic Mind. JAMA Psychiatry, 74(11), 1169–1170. https://doi.org/10.1001/jamapsychiatry.2017.2824
2. Mathalon, D. H., & Ford, J. M. (2008). Corollary Discharge Dysfunction in Schizophrenia: Evidence for an Elemental Deficit. Clinical EEG and Neuroscience, 39(2), 82–86. https://doi.org/10.1177/155005940803900212
3. Ford, J. M., Mathalon, D. H., Heinks, T., Kalba, S., Faustman, W. O., & Roth, W. T. (2001). Neurophysiological Evidence of Corollary Discharge Dysfunction in Schizophrenia. American Journal of Psychiatry, 158(12), 2069–2071. https://doi.org/10.1176/appi.ajp.158.12.2069
4. Ji, N., Venkatachalam, V., Rodgers, H. D., Hung, W., Kawano, T., Clark, C. M., Lim, M., Alkema, M. J., Zhen, M., & Samuel, A. D. (2021). Corollary discharge promotes a sustained motor state in a neural circuit for navigation. ELife, 10. https://doi.org/10.7554/elife.68848
So, what exactly does this mechanism do? In this event, whenever we move or speak, our brains send a copy for the motor command to sensory areas to cancel sensory re-afferent generated by self-motion, and effectively whispering: “Don’t be surprised, this sensation is coming from you.” In more concrete words, this interesting mechanism allows us to distinguish between what our movements cause and what the outside world causes. But... What if this mechanism deteriorates? This is the unexpected door that opens to the schizophrenic minds.
According to some considerable studies, the measured brain responses while participants spoke simple vowel letters and then listened to recordings of their own speech showed that their brains reduced auditory responses when speaking compared to listening. Consequently, in healthy individuals, it is understood that corollary discharge helps the auditory system dampen responses to their own voice. However, strikingly; patients with schizophrenia did not show this response and subsequently, this demonstrate that their brains failed to label self-generated speech as “self-made”. Even it is argued that this deficit can be represented as a fundamental dysfunction in schizophrenia because the schizophrenic brain cannot mark the internal actions and thoughts as self-generated, the door opens to unwanted experiences, such as hearing some voices that feels alien, or believing their actions are controlled by others. Therefore, this situation proves that corollary discharge is very important in terms of maintaining the boundary between us and our external world.
As final words, from our inability to tickle ourselves to the devastating symptoms of auditory hallucinations, corollary discharge reveals that how important the sensitivity adjustments of the brain’s feedback mechanism to separate the inner from the outer and the self-perception from the real world. Besides, this function also opens a controversial window into schizophrenia with showing how a subtle failure in this neural processing can cause an profound problem in defining what it means to be “me”.
References
1. Poletti, M., Gebhardt, E., & Raballo, A. (2017). Corollary Discharge, Self-agency, and the Neurodevelopment of the Psychotic Mind. JAMA Psychiatry, 74(11), 1169–1170. https://doi.org/10.1001/jamapsychiatry.2017.2824
2. Mathalon, D. H., & Ford, J. M. (2008). Corollary Discharge Dysfunction in Schizophrenia: Evidence for an Elemental Deficit. Clinical EEG and Neuroscience, 39(2), 82–86. https://doi.org/10.1177/155005940803900212
3. Ford, J. M., Mathalon, D. H., Heinks, T., Kalba, S., Faustman, W. O., & Roth, W. T. (2001). Neurophysiological Evidence of Corollary Discharge Dysfunction in Schizophrenia. American Journal of Psychiatry, 158(12), 2069–2071. https://doi.org/10.1176/appi.ajp.158.12.2069
4. Ji, N., Venkatachalam, V., Rodgers, H. D., Hung, W., Kawano, T., Clark, C. M., Lim, M., Alkema, M. J., Zhen, M., & Samuel, A. D. (2021). Corollary discharge promotes a sustained motor state in a neural circuit for navigation. ELife, 10. https://doi.org/10.7554/elife.68848