A Quick Guide to Mirror Neurons

This comes from Cell Press's Current Biology, a rare open access article available through the Science Direct portal. This quick guide to mirror neurons accompanied a few temporarily open access articles from previous journals that examined mirror neurons, their functions, and the validity of the claims made for them. This is from 2009, so the info is mostly correct, but not fully so.

Volume 19, Issue 21, 17 November 2009, Pages R971–R973

Mirror neurons 

Christian Keysers; Social Brain Lab, Department of Neuroscience, University Medical Center, Groningen, Groningen and Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Sciences (KNAW), Amsterdam
http://dx.doi.org/10.1016/j.cub.2009.08.026, How to Cite or Link Using DOI
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What are mirror neurons? Mirror neurons are multimodal association neurons that increase their activity during the execution of certain actions and while hearing or seeing corresponding actions being performed by others. Neurons responding to the sound or sight of some actions, but only to the execution of different actions, are not mirror neurons.

Where are mirror neurons found? Three research groups have reported the existence of mirror neurons in three regions of the macaque cortex (Figure 1). Pending systematic explorations, we do not know whether mirror neurons exist elsewhere in the macaque brain. Recently, mirror neurons have also been reported in the song-bird.

Figure 1. Mirror neurons.Left: regions in which mirror neurons have been recorded in the macaque; and right, voxels showing activity both during observation and execution in the human brain (from Gazzola and Keysers (2009)). Both brains have been partially inflated to reveal the sulci. Many brain regions have not yet been explored for mirror neurons in the monkey, hence the ‘?’s. IPS, intraparietal sulcus; PF/PFG, areas of the inferior parietal lobule.

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Do humans have mirror neurons? This issue has been highly contentious, with no individual piece of evidence generally accepted as definitive, but quite a lot of indirect evidence for human mirror neurons has been reported. First, if a subject moves, the power of the mu-rhythm in the electro-encephalogram (EEG) recorded from his or her brain decreases. Similarly, the EEG rhythm desynchronizes when the subject observes somebody else move. Second, behavioral experiments indicate that the execution of an action is facilitated by viewing someone else execute a similar action, but hindered by viewing an incompatible action. Moreover, transcranial magnetic stimulation (TMS) studies evidence that watching performance of an action facilitates the motor cortical representation of the muscles involved in doing the same action. This shows that some neurons involved in performing an action are indeed selectively activated by seeing a similar action — in other words, mirror neurons do exist somewhere in the human brain.

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