A Head Full of Mirrors

Yet another addition to the bucketload of literature on mirror neurons – this one by folks at UCLA. These guys inserted electrodes into the accessible brain areas of 21 patients who were having brain surgery for their epilepsy. Once the electrodes were in place and the patient was (presumably) sitting up in bed a relatively happy camper, they recorded activity from specific sets of brain cells, during three different conditions: performing a hand or facial movement, observing a 3 second video of a hand or facial movement, or reading a cue to move their hand or face but refraining from doing so.  They recorded activity in groups of brain cells in several brain areas – amygdala, hippocampus;  entorhinal cortex; parahippocampal gyrus; supplementary motor area; dorsal aspect of anterior cingulate; and rostral aspect of anterior cingulate. They categorised brain cells according to whether they only fired when the patient performed the movement; only when the patient observed the movement; during both observation and execution (the classic ‘mirror neuron’ idea); fired during observation of a frown and execution of a smile, or the other way around – these were called ‘non-matching neurons’. In short, between 6% and 14% of the brain cells were categorised as ‘mirror neurons’ (active during both performance and observation of a particular hand of facial movement). Similar proportions of non-matching brain cells were observed.

The authors conclude:

These findings suggest the existence of multiple systems in the human brain endowed with neural mirroring mechanisms for flexible integration and differentiation of the perceptual and motor aspects of actions performed by self and others

I think this means that they think there may be at least two mirror systems – one that gets excited when we observe a movement in a manner consistent with doing that movement and one that gets excited when we observe a movement in a manner that inhibits that movement.

It is certainly pretty sophisticated and elegant research – recording electrical activity within the brain. I am intrigued by a couple of things. I would have expected the fact that all of these data are from a group of people who had clear neurological dysfunction, sufficiently severe to warrant brain surgery, would be relevant to our interpretation of this.  I am also intrigued that although which brain cells were included was determined by clinical parameters to do with the patients’ epilepsy, there were mirror neurons (and the rest) in all of them. It seems we might have these mirror systems all over the brain – do we indeed have a head full of mirrors? Pat Wall probably wouldn’t be surprised by that idea – he firmly believed that we only perceive things according to what we might do about them (not HIS idea but the idea to which he subscribed).  I like the way these recent data fit into the metaphor of the brain as an orchestra – clearly these ‘mirror’ brain cells contribute to the perception or observation or interpretation of an observed movement AND to the execution of the movement and probably to a bunch of other things too – just like musicians contribute to many songs.  I like the metaphor because it provides an angle to convince patients that their brain cells, like their muscles, can be trained. Clearly we don’t know which ones and we can’t prove the theory in each patient but it is, I think, an elegant scaffold on which to hang some of what we do in rehabilitation. Anyway, off topic. If you can take on the tricky analysis and fancy pants language, the paper is well worth a read.

Mukamel R, Ekstrom AD, Kaplan J, Iacoboni M, & Fried I (2010). Single-Neuron Responses in Humans during Execution and Observation of Actions. Current biology : CB PMID: 20381353

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