You can recognize fear in faces even with a messed up amygdala if you have OK mirror neurons, sez a report about mirror neurons, the neural equivalent of unicorns

Mihov et al., “Mirroring Fear in the Absence of a Functional Amygdala,”Biological psychiatry 14 December 2012( in press), Figure 1

Although having a messed up amygdala can impair the ability to detect fear in others, apparently the mirror neuron network can compensate for this.

The paper: Mirroring Fear in the Absence of a Functional Amygdala
Yoan Mihov, Keith M. Kendrick, Benjamin Becker, Jacob Zschernack, Harald Reich, Wolfgang Maier, Christian Keysers, René Hurlemann, Biological psychiatry 14 December 2012 (Article in Press DOI: 10.1016/j.biopsych.2012.10.029)(Non-paywalled version here).

The paper is a twin study and we’re always amazed at twin studies. How do the researchers find the twins? Why do the twins agree to be poked and prodded? How do they feel if one is different from the other?  What about other siblings, do they feel left out?

Maybe our fascination is with the concept of having someone else who is genetically identical (practically) walking around — a clone.  Maybe a doppelgänger (“a paranormal double of a living person, typically representing evil or misfortune” according to Wikipedia).  As a general matter, we’re pro- evolution, and against cloning, because if people cloned themselves — no matter really how they tinkered around the edges of the DNA — there would be to much homogeneity and the human race wouldn’t last very long.

But this post is now veering into bioethics territory and we want to stick to the point: mirror neurons.

The 38 year old, female, monozygous twins in this particular study both had congenital amygdala damage, but one twin (“Patient 1″) could recognize fearful faces, and the other couldn’t.

So the researchers asked whether “mirror neuron networks” had anything to do with it. They showed the twins (and a control) images of fearful faces. The brain image above shows the area in Twin 1 lit up in response to fearful faces, that was not lit up in Twin 2, the twin who did not recognize fearful faces.

To us, “mirror neurons” are the unicorns of neuroscience. They are said to be the neurons that are activated to mirror the actions or intentions of others, to oversimplify, and some claim this network is important to empathy. Yet, despite all the press, mirror neurons only have circumstantial proof, it seems to us. Are they really a kind of cell? Or are they just other cells acting up?

Regardless, the authors state, “. . .[O]ur results suggest that the amygdala does not constitute an essential component of the human [mirror neuron network].. . . ”

We’re not sure what to make of this report, but our take-away is a confirmation that amygdala damage impairs the ability to recognize fear in others, and it’s not a certainty that there are other compensatory circuits.