Friday, April 02, 2010

Mirror Neurons - Deconstructing the Promise and Pitfalls of Current Research

Mirror neurons have been one of the hottest topics in neuroscience over the last 25 years, ever since the 1980s and 1990s, when Giacomo Rizzolatti (who was working with Giuseppe Di Pellegrino, Luciano Fadiga, Leonardo Fogassi, and Vittorio Gallese at the University of Parma, Italy) discovered these curious neurons in the brains of monkeys and, later, humans.

Among the loudest and most public fans of the potential of these neurons have been V.S. Ramachandran, who believes they might be very important in imitation and language acquisition.[2] and Marco Iacoboni, who is the author of Mirroring People: The Science of Empathy and How We Connect with Others (Farrar, Straus, & Giroux, 2008).

Here is a brief TED Talks video from Ramachandran on mirror neurons.

Dan Siegel has also placed a lot of emphasis on mirror neurons in his model of interpersonal and intrapersonal attunement - see The Mindful Brain: Reflection and Attunement in the Cultivation of Well-Being (W.W. Norton & Co., 2007).

I have been most interested in two areas of mirror neuron research (as well as their possible role in attachment theory, which is what Siegel explores), empathy and theory of mind. These quotes are from Wikipedia, which offers a surprisingly well-balanced look at this topic.


Stephanie Preston and Frans de Waal,[35] Jean Decety,[36][37] and Vittorio Gallese[38][39] have independently argued that the mirror neuron system is involved in empathy. A large number of experiments using functional MRI, electroencephalography (EEG) and magnetoencephalography (MEG) have shown that certain brain regions (in particular the anterior insula, anterior cingulate cortex, and inferior frontal cortex) are active when a person experiences an emotion (disgust, happiness, pain, etc.) and when he or she sees another person experiencing an emotion.[40][41][42][43][44][45][46] However, these brain regions are not quite the same as the ones which mirror hand actions, and mirror neurons for emotional states or empathy have not yet been described in monkeys. More recently, Christian Keysers at the Social Brain Lab and colleagues have shown that people who are more empathic according to self-report questionnaires have stronger activations both in the mirror system for hand actions[47] and the mirror system for emotions[45], providing more direct support for the idea that the mirror system is linked to empathy.

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Theory of mind

In Philosophy of mind, mirror neurons have become the primary rallying call of simulation theorists concerning our 'theory of mind.' 'Theory of mind' refers to our ability to infer another person's mental state (i.e., beliefs and desires) from their experiences or their behavior. For example, if you see a girl reaching into a jar labeled 'cookies,' you might assume that she wants a cookie (even if you know the jar is empty) and believes that there are cookies in the jar.

There are several competing models which attempt to account for our theory of mind; the most notable in relation to mirror neurons is simulation theory. According to simulation theory, theory of mind is available because we subconsciously empathize with the person we're observing and, accounting for relevant differences, imagine what we would desire and believe in that scenario.[56][57] Mirror neurons have been interpreted as the mechanism by which we simulate others in order to better understand them, and therefore their discovery has been taken by some as a validation of simulation theory (which appeared a decade before the discovery of mirror neurons).[58] More recently, Theory of Mind and Simulation have been seen as complementary systems, with different developmental time courses.[59][60][61]

I think there is more evidence so far for the presence of an emotional system of mirror neurons than there is for the Theory of Mind model.

The Compassionate Instinct: The Science of Human Goodness, edited by Dacher Keltner, Jeremy Adam Smith, and Jason Marsh (W.W. Norton & Company, 2010) looks at some of the evidence for the empathy concept of mirror neurons. For those who are interested, the essays and articles in that book all appeared originally in Greater Good Magazine, published by U.C. Berkeley's Greater Good Science Center. There is a lot of very good info at the site, including stuff for parents and educators.

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To be fair, I want to include a couple of the objections to mirror neuron theory. These two sections also come from the Wikipedia entry.

Evidence against mirror neurons

Three recent studies cast doubt on the importance of mirror neurons in the human brain.[23][28][29] These fMRI studies suggested that the signal changes seen in 'mirror neuron regions' of the human brain are not necessarily due to the firing of mirror neurons themselves, but may reflect the responses of other neurons in these brain areas. The studies found evidence of movement selective activity for both observed and executed movements, i.e., for one population of visual neurons that respond selectively to observed movements and a separate population of motor neurons that respond selectively to executed movements, but there was no evidence of mirror neurons that would respond selectively to the same observed and executed movement. The authors of these papers concluded that although there may be movement-selective mirror neurons in the human brain, they make up only a minority of the neurons active during observation or execution of movement and do not dominate the fMRI responses in putative mirror system areas of the brain. Whereas these three papers failed to find evidence of mirror neurons that would respond selectively to the same observed and executed movement a more recent study has successfully demonstrated this effect [30]. These authors argue that they were able to find the effect where others had previously failed because their study was optimally designed to find mirror neurons in the human inferior frontal gyrus.

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Although many in the scientific community have been excited about the discovery of mirror neurons, there are some researchers who express skepticism in regards to the claims that mirror neurons can explain empathy, theory of mind, etc. Greg Hickok, a cognitive neuroscientist at UC Irvine, has stated that "there is little or no evidence to support the mirror neuron=action understanding hypothesis and instead there is substantial evidence against it."[66] Hickok also published a detailed analysis of these problems in his paper, "Eight problems for the mirror neuron theory of action understanding in monkeys and humans."[67] The eight problems he refers to are:

  • There is no evidence in monkeys that mirror neurons support action understanding.
  • Action understanding can be achieved via non-mirror neuron mechanisms.
  • The primary motor cortex (M1) contains mirror neurons.
  • The relation between macaque mirror neurons and the “mirror system” in humans is either non-parallel or undetermined.
  • Action understanding in humans dissociates from neurophysiological indices of the human “mirror system.”
  • Action understanding and action production dissociate.
  • Damage to the inferior frontal gyrus is not correlated with action understanding deficits.
  • Generalization of the mirror system to speech recognition fails on empirical grounds.
Then there is also this article from The Neurocritic posted the other day. The Neurocritic (who seems to really dislike the hype around mirror neurons) references another post that deconstructs an article by Giacomo Rizzolatti and his co-author (citation below). It's a brief argument, but it's useful.

Mirror Neuron Death March

Greg Hickok at Talking Brains has a series of posts dismantling the mirror neuron theory of action understanding. Actually, he lets one of the leading researchers in the field, Giacomo Rizzolatti [and his coauthor] dismantle the theory himself in a recent review paper (Rizzolatti & Sinigaglia, 2010). Greg points out the inconsistencies in the NRN article...
So, mirror neurons, those cells that fire during specific actions such as grasping-with-the-hand and while watching the same specific action -- the very cells that got everyone SO excited -- are not involved in action understanding. Rather, according to R&S, action understanding is achieved by cells that do not code for actions at all, but something higher level, goals/intentions.

It's worth noting that R&S directly contradict themselves in the sidebar definition of "Mirror-based action understanding":
The comprehension of an observed action based on the activation of a motor programme in the observer’s brain. p. 265
A motor program presumably controls a specific action, such as grasping-with-the-hand, not an action-independent goal or intention.
...and also the problems with promoting an unfalsifiable theory:
I think the mirror neuron folks have a serious problem on their hands: there is apparently no empirical result that can falsify the theory. If a mirror neuron shows up in an unexpected place, it is a new part of the mirror system. If a mirror neuron's activity dissociates from action understanding, it was not coding understanding at that moment. If damage to the motor system doesn't disrupt understanding, it is because that part of the motor system isn't mirroring.
As another long-time mirror neuron skeptic, I highly recommend this series:

Mirror Neurons - The unfalsifiable theory

Mirror neurons support action understanding -- "from the inside"?

Self-destruction of the mirror neuron theory of action understanding


Rizzolatti, G. & Sinigaglia, C. (2010). The functional role of the parieto-frontal mirror circuit: interpretations and misinterpretations. Nature Reviews Neuroscience, 11 (4), 264-274.

He gives you some links to follow for more "debunking."

Finally, here is an article debunking the newest "use" of mirror neuron theory (yes, all of this is still a theory and the research is still working to confirm the original hypotheses) - the claim that the aesthetic experience arises from simulating the sensory-motor experience of the subject IN the painting. Huh?!

This excellent, but short article comes from Chris at Mixing Memory - a very fine cognitive science blog.

The Simulation Theory of Aesthetics

Category: Cognitive Neuroscience
Posted on: March 18, 2007 10:24 AM, by Chris

With a paper by Freedberg and Gallese, to be published in Trends in Cognitive Sciences, mirror neurons have made their way into neuroaesthetics (at some point, someone like Gallese will publish a paper arguing that mirror neurons explain everything, and we'll begin to wonder what the hell the rest of the brain is for). Here's the abstract from the paper1:

The implications of the discovery of mirroring mechanisms and embodied simulation for empathetic responses to images in general, and to works of visual art in particular, have not yet been assessed. Here, we address this issue and we challenge the primacy of cognition in responses to art. We propose that a crucial element of esthetic response consists of the activation of embodied mechanisms encompassing the simulation of actions, emotions and corporeal sensation, and that these mechanisms are universal. This basic level of reaction to images is essential to understanding the effectiveness both of everyday images and of works of art. Historical, cultural and other contextual factors do not preclude the importance of considering the neural processes that arise in the empathetic understanding of visual artworks.

It's a good thing that they're challenging "the primacy of cognition in response to art," because God knows those other neuroaesthetic theories were heavy on the cognition and light on the sensory-motor aspects of aesthetic experience (cough, cough). Is it just me, or do the embodied/simulation people have serious persecution complexes? Anyway, I offer this without further comment.

OK, I tried, but I can't resist one more comment. One of the main arguments in the paper relies on research on the representation of pain. The basic idea is this. When we see a piece of visual art like, say, this one (they use a different drawing from the "Disasters of War" series, but I like this one damnit!):


According to Freedman and Gallese, the way we represent the pain that poor sap being stabbed by a spear is experiencing is by simulating the sensory-motor experience of pain in our own brains. As evidence for this view, they cite a couple papers (actually, they don't cite them, they refer to another paper by Gallese in which he cites them, which is... I'm just not going to say anything) that both describe similar findings. For example, Singer et al.2 describe a study in which they measured individuals' brain activity during a painful experience, and again while those individuals watched a loved one undergo the same experience. Singer et al. found overlapping activation during both imaging sessions, but not in the areas associated with feeling pain. Instead, the overlaps occurred in the areas associated with the emotions that the painful experience caused. In other words, Singer et al.'s study produced the revolutionary finding that empathy is feeling the emotions that others are (likely) feeling! Wow. But, umm... that's not what the simulation theory would predict. The simulation theory would predict that in addition to having the same emotions when experiencing or witnessing pain, we should also "simulate" the pain in the same regions where we experience pain. But Singer et al. didn't find that. Hell, the title of the Singer et al. paper is "Empathy for pain involves the affective but not the sensory components of pain" (my emphasis). So why would Freedman and Gallese use their results to argue for a simulation theory of aesthetics? I dare not speculate.

1Freedman, D., & Gallese, V. (In Press). Motion, emotion and empathy in esthetic experience. Trends in Cognitive Sciences.
2Singer, T., Seymour, B., O'Doherty, J., Kaube, H., Dolan, R.J>, & Frith, C.D. (2004). Empathy for pain involves the affective but not the sensory components of pain. Science, 303, 1157-1162.
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I am not yet ready to give up on mirror neurons. There is a LOT of research going on in this field. For those who are interested, the National Institute of Mental Health (NIMH) has a ton of links to studies they have funded or partially funded.

As even this last objection shows, there is much more likelihood of an emotional system of mirror neurons than there is for a physical system. On the other hand, I think some people can learn by watching others perform an action. Maybe this type of sensory-motor mirror neuronn system only exists (in its strong form) in those people who tend toward bodily-kinesthetic intelligence. That would be a good study.

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