Mirror neurons and autism

December 31, 2007

—Nina Pierpont, MD, PhD

Have you ever wondered how you can tell at a glance what someone is feeling?

The answer is patches of brain cells known as mirror neurons.  Mirror neurons are arranged in networks linking incoming sight and sound with outgoing muscle (motor) responses.  Moreover, we now know that one part of the mirror neuron network connects to what is called the limbic circuit, governing emotions.

Humans learn by imitating, especially as young children.  It’s amazing how children absorb the personalities and habits, including the language, of their earliest environments.  Throughout life, fine-tuned imitation remains essential for tracking the social environment.

Mirror neurons are essential for this imitation and, hence, for learning of all sorts.

In monkeys, mirror neurons fire when the monkey reaches for a banana.  The same neurons activate when the monkey sees another monkey (or human) likewise reaching for a banana.  Within patches of mirror neurons, some cells fire more vigorously when the monkey sees the action, and others fire more vigorously when the monkey itself performs the action.  Imitation – monkey both sees and does—generates the strongest neuron response.

We can take this a step further.  Some mirror neurons fire if the monkey reaches for a hidden banana, but don’t fire if it reaches behind a screen where it knows there is no banana.  Other neurons fire if the context suggests the banana is going to be eaten, versus put in a box.  In other words, mirror neurons encode abstract ideas (such as the idea of a banana, even if it can’t be seen) and complex ideas like intentions or goals.

In humans, mirror neuron activity is studied by a scanning technique called functional MRI.  A person is awake with his head in a specially designed MRI scanner while he does an experimental task.  The MRI detects how much blood flows to different parts of the brain as different tasks are done.  Increased blood flow indicates more activity in that part of the brain at that moment.

With all this as background, consider what happens when you look at someone’s facial expression.  If you have normally functioning mirror neurons, you immediately feel the emotion expressed in the other person’s face.  The mirror neuron fires and sends its impulse to the emotional (limbic) circuit, just as if you had made the expression yourself.  This capacity is the basis for empathy and the awareness that other people have feelings and points of view.

Now consider an autistic child.  Ten normal children and ten high-functioning autistic children, about 12 years old and matched for age and IQ, took part in a particular study.  All 20 kids looked at and imitated facial expressions in pictures during functional MRI.  The results were striking.  The area in the frontal lobes known to house the mirror neurons, and the limbic (emotional) circuits, did not show the same activity in autistic children that they did in normal children, even though the autistic children paid attention and did the face imitations just as well.

The autistic children, it turns out, were compensating for their deficit in mirror neurons by using a different part of their brain.

We now begin to understand Dr. Temple Grandin, the high-functioning autistic woman I have already discussed in this column.  As a child, Grandin understood speech, yet she had a dickens of a time learning to produce the words themselves—which is the imitation part of speech, dependent on those mirror neurons functioning properly.  Likewise, growing older, Grandin had to create rules for herself for proper and acceptable social interactions.  Again, a mirror neuron deficit goes a long way toward explaining her inability to understand people intuitively.

A whole new perspective on autism has thus opened up within the last several years.  For the first time we begin to see why autistic children are less interested and skilled at human interactions and communication.  Why they live in their own world, unless actively engaged, over and over, by their caretakers.  Why they do not imitate well, but persist remotely in their own kinds of play.  Why their play tends to be mechanical, rather than representing the complex social interactions around them.  And why speech develops late.

We should be cheering autistic children like Temple Grandin who, by tremendous will-power and brilliance, manage to enlist other parts of their brain to compensate for something you and I simply take for granted—the gift of telling at a glance what someone else is feeling.