Autism Linked To Mirror Neuron Dysfunction
Findings May Lead to Early Diagnosis of the Disorder
and Possible Therapies
By Inga Kiderra
Seeing is doing –
at least it is when mirror neurons are working normally. But
in autistic individuals, say researchers from the University
of California, San Diego, the brain circuits that enable people
to perceive and understand the actions of others do not behave
in the usual way.
According to the new
study, currently in press at the journal Cognitive Brain
Research, electroencephalograph (EEG) recordings of 10
individuals with autism show a dysfunctional mirror neuron system:
Their mirror neurons respond only to what they do and not to
the doings of others.
child with autism, wearing an EEG cap to measure brain-waves,
watches video of a moving hand.
Credit: Lindsay Oberman
Mirror neurons are
brain cells in the premotor cortex. First identified in macaque
monkeys in the early 1990s, the neurons – also known as
“monkey-see, monkey-do cells” – fire both
when a monkey performs an action itself and when it observes
another living creature perform that same action. Though it
has been impossible to directly study the analogue of these
neurons in people (since human subjects cannot be implanted
with electrodes), several indirect brain-imaging measures, including
EEG, have confirmed the presence of a mirror neuron system in
The human mirror neuron
system is now thought to be involved not only in the execution
and observation of movement, but also in higher cognitive processes
– language, for instance, or being able to imitate and
learn from others’ actions, or decode their intentions
and empathize with their pain.
Because autism is characterized,
in part, by deficits in exactly these sorts of social interaction
and communication skills, previous research has suggested that
a dysfunctional mirror neuron system may explain the observed
pathology. The current findings, the researchers say, lend substantial
support to the hypothesis.
The UC San Diego team
collected EEG data in 10 males with autism spectrum disorders
who were considered “high-functioning” (defined
as having age-appropriate verbal comprehension and production
and IQs above 80) and 10 age- and gender-matched control subjects.
The EEG data was analyzed
for mu rhythm suppression. Mu rhythm, a human brain-wave pattern,
is suppressed or blocked when the brain is engaged in doing,
seeing or imagining action, and correlates with the activity
of the mirror neuron system. In most people, the mu wave is
suppressed both in response to their own movement and to observing
the movement of others.
Subjects were tested
while they moved their own hands and while they watched videos
of visual white noise (baseline), of bouncing balls (non-biologic
motion) and of a moving hand.
As expected, mu wave
suppression was recorded in the control subjects both when they
moved and when they watched another human move. In other words,
their mirror neuron systems acted normally. The mirror neurons
of the subjects with autism spectrum disorders, however, responded
anomalously – only to their own movement.
provide evidence that individuals with autism have a dysfunctional
mirror neuron system, which may contribute to many of their
impairments – especially those that involve comprehending
and responding appropriately to others’ behavior,”
said Lindsay Oberman, first author of the paper and UCSD doctoral
student working in the labs of senior authors V.S. Ramachandran,
director of the Center for Brain and Cognition, and Jaime Pineda,
director of the Cognitive Neuroscience Laboratory.
The current study,
the researchers say, adds to understanding the neural basis
of autism and may point the way to early diagnosis and to potential
A first step, Ramachandran
said, might be to test those individuals who seem to have a
greater genetic likelihood of autism: the younger siblings of
those already diagnosed.
Though EEG is not at
present designed to measure the brain rhythms of low-functioning
autistics – whose many repetitive movements confound EEG
signals and where mental retardation also plays a significant
role in behavioral deficits – it can be used as a tool
for earlier diagnosis of high-functioning autistics, whose disorder
today is typically not recognized until age 3 or 4 and often
Earlier diagnosis in
turn could lead to earlier interventions. One therapeutic possibility
suggested by the study’s findings is biofeedback.
Pineda, who also works
on a number of brain-computer interface projects, says that
the mu rhythm is one that we most readily learn to control.
“We can learn
to increase or decrease the strength of the mu signal at will.
By imagining action, subjects are able to move a paddle in a
computer game of ‘Pong’ after just four to six hours
of practice,” he said. “Because this rhythm is one
that we have access to volitionally, it may prove useful in
Another possible therapy
would involve ordinary mirrors. Ramachandran has successfully
treated amputees who experience pain or paralysis in their missing,
or “phantom,” limbs by using a mirror reflection
of their healthy limb to “trick” their brains into
believing that the missing limb has been restored to pain-free
motion. Since autistics’ mirror neurons respond to their
own motion, the researchers say, perhaps their brains can be
induced to perceive their own reflected movements as the movements
of another human being.
“We have a long
way to go before these therapeutic possibilities are a reality,
but we’re that much closer now that we’ve linked
autism to a specific region of the brain,” said Ramachandran.
“More than just documenting a brain anomaly in autism,
we’ve been able to relate symptoms that are unique to
the disorder – loss of empathy and imitative skills –
to the function of a particular circuit, the mirror neuron system.”
Other authors on the
study are: Eric Altschuler, former UCSD postdoctoral researcher
now at the Mt. Sinai School of Medicine in New York, who with
Ramachandran and Pineda originally presented preliminary findings
on mirror neuron dysfunction in one autistic child in 2000;
Edward Hubbard, recent UCSD graduate now at the French National
Institute of Health (INSERM) in Paris; and UCSD graduate student
The team is now pursuing
another, related line of research: Are mirror neurons involved
in the ability to understand metaphors? Autistic individuals
typically have difficulties with metaphors, often interpreting
them literally, and the researchers believe this too may be
connected to a dysfunctional mirror neuron system.
“Even as the
clinical study of mirror neurons is giving us insights into
autism and other disorders,” Ramachandran said, “it
is also giving us glimpses of a host of uniquely human –
and elusive – mental capacities: making metaphors and
passing on proverbs, to name just two.”
Media Contact: Inga
Kiderra, (858) 822-0661