Giacomo Rizzolatti is a neuroscientist. With his unruly hair and moustache, he looks like a reincarnation of Albert Einstein. He is excitable, enthusiastic and friendly, and he runs a busy laboratory in Parma, Italy.
Rizzolatti records the activity of single neurons inside the brains of monkeys. In the frontal cortex are neurons which are active whenever the monkey reaches to grasp something, such as a peanut. The recording device can be hooked up to a speaker system, so that whenever a neuron fires you hear a crackling sound. One day, Rizzolatti was surprised to hear this sound, not only when the animal itself reached, but also when a person in front of the animal reached for the nut. Neurons that respond both when the monkey makes a movement and when it observes the same movement made by an individual have come to be known as mirror neurons. They are also described as ‘monkey see, monkey do’ neurons.
To neuroscientists, this discovery came as a revelation; indeed, one prominent scientist remarked that mirror neurons would do for psychology what deoxyribonucleic acid (DNA) has done for biology. You may well wonder why. The brain has traditionally been viewed as an input-output device, with some neurons responding to particular inputs, such as a face or the call of another member of the species, and some responding when the animal makes some movement, such as grasping something or emitting a cry. Other neurons may lie in between input and output, perhaps representing thought, as when we ponder the meaning of a question before replying. Mirror neurons, though, seem to imply a direct mapping between input to output, as though we have a ready-made system for understanding the bodily actions of others in terms of our own actions. Perhaps you have found yourself squirming on the couch as you watch sport on television, in synchrony with the ‘flannelled fools’ or ‘muddied oafs’ on the screen. You can blame your mirror neurons.
Mirror neurons have proved to be quite versatile. In the monkey, they fire not only when the animal sees an action, but also when it hears the sound of a familiar action, such as paper being torn or nuts being cracked open. Brain-imaging experiments show that we humans also have mirror neurons, and they respond to a wide variety of bodily actions. They enable us to resonate with the thoughts and feelings of others, as reflected in their actions, providing a natural explanation for human empathy and the theory of mind discussed in the previous essay. Indeed autism, the condition characterised by an inability to understand the mental states of others, is now widely attributed to a failure of the mirror-neuron system.
Mirror neurons may also help explain how we understand speech, which seems to border on the miraculous. Speech consists of packets of sound delivered at high rates, complicated by the fact that sounds that you hear as the same can actually be very different, depending on the contexts in which they are embedded. For example, b sounds in words like battle, bottle, beer, bug, rabbit, Beelzebub or flibbertigibbet probably sound much the same to you, but the actual acoustic streams created by these b sounds varies widely, to the point that they actually have little in common. This surprising fact, discovered only when sophisticated ways of analysing speech sounds were developed, has long been the bane of scientists attempting to programme computers to recognise speech. Computers can now be painstakingly programmed to identify spoken words, but with only moderate success, and nothing like the facility of a normal four-year-old.
One solution to this problem is the so-called motor theory of speech perception, which holds that we perceive speech, not in terms of its acoustic properties, but in terms of how it is produced. The discovery of mirror neurons provided a strong boost for this theory. Thanks to your mirror neurons, you effectively map the speech of others directly onto your own mechanism for producing that speech. Monkey see, monkey do becomes listener hear, listener do.
Mirror neurons almost certainly don’t come preprogrammed. They need to be tuned. Much of that tuning probably happens in childhood. My guess is when infants babble, they are in effect tuning themselves to the sounds of speech, and mapping them onto their own production of sounds. That tuning is specific to the sounds of their native language, which is why foreign languages sound not only incomprehensible, but also nearly impossible to parse into their underlying sound patterns. And we are of course tuned into other actions as well, such as sporting skills and playing musical instruments.
It is fitting that neurons were first discovered in the context of arm movements. Rizzolatti gestures enthusiastically as he talks, no doubt activating his own counterparts of the neurons he found in the monkey brain. Mirror neurons could only have been discovered by an Italian.