Mirror neurons have been widely described as a crucial discovery and possibly ‘the next big thing’ (I’m not sure, when I come to think about it, what the last big thing was). Ramachandran describes them as ‘empathy neurons’ or even ‘Dalai Lama neurons’, and others have been almost equally enthusiastic. But are they really so good? The trenchant title of a short paper by Emma Borg asks ‘If mirror neurons are the answer, what was the question?’.
Your mirror neurons fire both when you perform an action, and when you see someone else perform that action. Borg contrasts them with ‘canonical neurons’, which fire in response to an object offering the right kind of affordances. In other words, if I’ve got it right, we have a large group of neurons that fire when we, for example, take a sip of tea: some of them are mirror neurons which also fire when we see someone else drink; others are canonical neurons which also fire when we see a cup or a teapot – ‘tea-drinking things’.
At a basic level, the argument that mirror neurons might help to explain empathy, or our understanding of other people, is clear enough. When I see A do x, the mirror neurons mean my mental activity has at least some limited features in common with A’s (presumed) mental activity, or at least what A’s mental activity would be if A were me. You can see why this resembles telepathy of a sort, and it seems a natural hypothesis that it might form the basis of our understanding of other people. One of the many theories on offer to explain autism, in fact, holds that it is caused by a deficiency in mirror neuron activity. Apparently there is evidence to show that autistic people don’t show the same kinds of activity in the relevant regions as normal people when they observe other people’s behaviour. It could be that the absence of mirror neuron activity has left them with no basis for a ‘theory of mind': of course it could also be that the absence of an effective theory of mind, caused by something else altogether, is somehow suppressing the activity of their mirror neurons.
Borg’s target is the idea that mirror neurons in themselves give us the ability to attribute high-level intentions to other people, by running simulated intentions of our own that match the observed actions of the other person. The initial idea is roughly that when we see someone lift a cup, some of our neurons start doing that tea-cup lifting thing in sympathy (off-line in some way, of course, or we should grab a cup ourselves). This is like harbouring the intention of lifting the cup, but we are able to attribute the intention to the other person. However, this only gets us as far as the deliberate lifting of the cup: it has been further claimed that mirror neurons give us the ability to deduce the over-arching intention – drinking a cup of tea. The claim is that mirror neurons not only resonate with the current action but also more faintly (or rather, in smaller numbers) with the next likely action, and this provides a guide to the higher-level activity of which the single act is part.
Borg points out that actions in themselves are highly ambiguous. I may lift a cup to test its weight, or to stop you getting it, rather than in order to drink from it. It’s certainly not the case that every basic act dictates its successors, or we should be trapped in a cycle of stereotyped behaviour. When we run our mental simulation then, how can we know which secondary echoes we need to start off in our mirror neurons – unless we already know which higher-level course of action we are dealing with? In short, mirror neurons are not enough unless we already have a working theory of mind from some other source.
We might argue that we don’t need to know the intention in advance, because the simulation allows us to test out several different higher-level courses of action at once. But again, the mere observation of the single act before us won’t allow us to choose between them. In the end we’ll always be driven back to appealing to something more than mere mirror neuron activity. None of this suggests that mirror neurons are uninteresting, but perhaps they are not, after all, going to be our Rosetta Stone in deciphering the brain.
Borg describes her argument as anti-behaviourist, resisting the idea that intentions and other ‘mentalistic’ states can be reduced to simple patterns of activity. Fair enough, but given that behaviourism doesn’t put up much of a fight these days, it may be more interesting that it bears a distinct resemblance – or so it seems to me – to many other problems which have afflicted attempts to reduce or naturalise intentionality, up to and including the frame problem. It’s as though we were trying to find a way through an impenetrable hedge: every so often someone finds a promising looking thin patch and starts to shove through; but sooner or later they meet one or another stretch of suspiciously-similar looking brick wall.