ALL ABOARD! The mirror neuron hype train

March 5th, 2024

Written by: Barnes Jannuzi

Interacting with others is fundamental to the human experience, and we are really good at it! For example, read this situation and try to figure out what is going on: “A person is standing in front of a cashier at Chipotle. They are moving their hands quickly and patting the sides and back of their pants with increasing intensity. Another person is standing behind the counter and has their hands on their hips and is looking at the customer.” What is going on? Even though there was no mention of payment or a transaction in this example, it seems fair to assume that the person wants to buy something but has unfortunately lost their wallet. It is almost difficult not to apply some emotion to the situation. Perhaps the customer is panicked, while the cashier may be annoyed. We can 1) interpret how others are moving 2) observe the context of a situation 3) determine why they are doing what they are doing and 4) how/if we could do the same thing is something which most of us excel at. 

Our ability to form these opinions relies on the understanding that other people have minds rich with emotions, beliefs, and thoughts as complex as our own. This understanding is called theory of mind. One of the biggest unanswered questions about the human experience is where this theory of mind comes from. As such, whenever there is a finding in neuroscience that seems to come close to unlocking this mystery, people get excited… and sometimes overly so. At least, this was the case for a promising discovery of “mirror neurons”. Hop on board the mirror neuron express and we’ll embark on a journey with stops to explore the spark of discovery, the explosion of scientific investigation and over-promises made by popular culture, the reckoning of evidence, and finally a reflection on a lesson learned.

Stop #1: Spark of Discovery

The train is fueled up and ready to go. 

Surprisingly, one of the closest insights into theory of mind was discovered by accident as neuroscientists studied movement control. The neuroscientists were recording the activity of a neuron that became active as a monkey grasped an object. Then, something amazing happened. As the scientist picked up the object to reposition it, the same neuron lit up with activity even though the monkey hadn’t grasped anything themself! Amazingly, these neurons respond to a motion or action no matter who was doing the action (Fig. 1). We had long known of the existence of neurons that activate when seeing and neurons that activate when moving, but a single one that does both has the potential to be an important center of the brain which not only tie these two things together, but also be the basis of many of the amazing things that the brain can do. These special cells are Mirror Neurons^1,2 and in the coming decades would be found in several other brain areas, as well as in humans^7,8. 

The mirror neuron hype train had started out from the station.

Stop #2: Rise of Investigation

Neuroscientists immediately had lots of interesting questions and ideas. Many thought that mirror neurons might help us understand the motions of others by causing our brains to experience the same motions that we observe. Of course, motion isn’t the only thing we might want to understand about others, so one exciting possibility was that we might also have mirror neurons for other things like emotions, which may explain human empathy. How better to explain the feeling of understanding what it is like to walk in someone else’s shoes than your brain literally experiencing not only the motions, but also the emotions held and expressed by others? Indeed, mirror neurons seemed to have promise to be an important step to human theory of mind, but more evidence would be needed for that claim. Additionally, neuroscientists also wondered if these malfunction in these neurons could explain differences in social behaviors in people with autism. Could autism itself be caused by malfunctioning mirror neurons?⁹

Another behavior neuroscientists thought might be explained by mirror neurons is imitation. The tendency to directly mimic the behavior of others is an important part of development and often an unconscious part of social interaction throughout adulthood¹⁰. Could mirror neurons allow us to directly mimic the behaviors of others? 

Unfortunately, these valid questions were quickly swept up in popular narratives outside of science and soon questions like “Do mirror neurons lead to empathy?” turned into statements like “mirror neurons can explain human empathy”. It is understandable why, these ideas seem to make a lot of sense at face value and seem to form a cohesive story. But ideas without evidence to back them up are just ideas, not facts.

The mirror neuron hype train was going at full speed, and can’t slow down. 

Stop #3: Reckoning of Evidence

It has been just over 30 years since the first discovery of mirror neurons. What have we actually learned? What has held up to the hype? Despite hope that mirror neurons might be able to explain empathy and other complex parts of human interaction, there is still no substantial evidence that mirror neurons are involved with anything more than interpreting the motion of others^3,4. Additionally, when looking at the brain activity of areas that contain mirror neurons in individuals with autism, there seem to be no evidence that malfunctioning mirror neurons might cause autism despite the initial hope that they might¹¹.

The train ran out of track.

Although scientists would eventually test the questions that had been raised, it was not fast enough for unsupported claims to become widespread. Unfortunately, this has caused many myths to linger even to this day. For example, that mirror neurons are the cause of empathy and components of theory of mind, or that malfunctions in these neurons lead to autism.

But it was not all a waste.

One area in which mirror neurons have lived up to initial hopes is in explaining imitation. When neuroscientists temporarily disable parts of the brain that contain mirror neurons, participants temporarily struggle to imitate behaviors. This suggests that mirror neurons might play an important role in allowing us to imitate others^5,6. 

Final Stop: Reflections

It seems unlikely that mirror neurons will turn out to be the source of theory of mind, it does not mean the investigation of them has been fruitless or even that it is over. It is not only valuable, but critical that we never stop asking questions about how things work, coming up with ideas of how they might work, and testing those ideas by trying to prove them wrong. The process by which questions of interest become statements of fact is important, challenging, and errors can be dangerous. In fact, modern science as we know it is built upon this process, and careful navigation of it is what is known as the scientific method. However, it is equally important that we as learners and question-askers are careful not to let ideas that seem to make a lot of sense turn into unproven statements and claims. 

The mirror neuron hype train was not a wasted effort, we learned a lot about some very interesting neurons and what they are and (equally importantly) are not responsible for. The breakdown of our train has come primarily with the communication of that science to the public. Although we should all get excited by extraordinary ideas and questions, we should also keep that excitement in check to make sure it does not get ahead of truth. We must always remember that “extraordinary claims require extraordinary evidence.”- (Carl Sagan) 

References 

1. di Pellegrino, G., Fadiga, L., Fogassi, L. et al. Understanding motor events: a neurophysiological study. Exp Brain Res 91, 176–180 (1992). https://doi.org/10.1007/BF00230027
2. Gallese V, Fadiga L, Fogassi L, Rizzolatti G. Action recognition in the premotor cortex. Brain. 1996 Apr;119 ( Pt 2):593-609. doi: 10.1093/brain/119.2.593. PMID: 8800951.
3. Thompson EL, Bird G, Catmur C. Conceptualizing and testing action understanding. Neurosci Biobehav Rev. 2019 Oct;105:106-114. doi: 10.1016/j.neubiorev.2019.08.002. Epub 2019 Aug 5. PMID: 31394116.
4. Heyes C, Catmur C. What Happened to Mirror Neurons? Perspect Psychol Sci. 2022 Jan;17(1):153-168. doi: 10.1177/1745691621990638. Epub 2021 Jul 9. PMID: 34241539; PMCID: PMC8785302.
5. Heiser, M., Iacoboni, M., Maeda, F., Marcus, J., & Mazziotta, J. C. (2003). The essential role of Broca’s area in imitation.  European Journal of Neuroscience,  17, 1123–1128.
6. Catmur C, Walsh V, Heyes C. Associative sequence learning: the role of experience in the development of imitation and the mirror system. Philos Trans R Soc Lond B Biol Sci. 2009 Aug 27;364(1528):2369-80. doi: 10.1098/rstb.2009.0048. PMID: 19620108; PMCID: PMC2865072.
7. Mukamel R, Ekstrom AD, Kaplan J, Iacoboni M, Fried I. Single-neuron responses in humans during execution and observation of actions. Curr Biol. 2010 Apr 27;20(8):750-6. doi: 10.1016/j.cub.2010.02.045. Epub 2010 Apr 8. PMID: 20381353; PMCID: PMC2904852.
8. Kilner JM, Neal A, Weiskopf N, Friston KJ, Frith CD. Evidence of mirror neurons in human inferior frontal gyrus. J Neurosci. 2009 Aug 12;29(32):10153-9. doi: 10.1523/JNEUROSCI.2668-09.2009. PMID: 19675249; PMCID: PMC2788150.
9. Iacoboni M, Dapretto M. The mirror neuron system and the consequences of its dysfunction. Nat Rev Neurosci. 2006 Dec;7(12):942-51. doi: 10.1038/nrn2024. Epub 2006 Nov 8. PMID: 17115076.
10. Over, H. (2020). The social function of imitation in development. Annual Review of Developmental Psychology, 2(1), 93–109. https://doi.org/10.1146/annurev-devpsych-033020-024051 
11. Hamilton AF. Reflecting on the mirror neuron system in autism: a systematic review of current theories. Dev Cogn Neurosci. 2013 Jan;3:91-105. doi: 10.1016/j.dcn.2012.09.008. Epub 2012 Oct 13. PMID: 23245224; PMCID: PMC6987721.

Cover Photo by Tambon Ratsada on Unsplash.