From Perception to Action
And what’s in between?
A thought problem
• “Hold it!”, you shout, because you spot the problem
immediately…
• The brain exhibits functional specialization, but the
functions are complex and dynamic
– E.g. catching a ball, driving a car, reading a book, running
– Each example requires tight integration of perception and
action
• “motor systems”
are perception
systems as well
Complexities of modularity
• Some cells in “association” cortex exhibit properties
that cannot be described without reference to both
input and output systems
For example…
• Some cells in
basal ganglia
have visual
receptive fields
that are locked to
arm location
rather than
Mirror Neurons
The perception – action system
What are Mirror Neurons?
• Mirror neurons are cells that fire when a monkey (or
person?) performs an action or when it views another
animal performing that same action
What are Mirror Neurons?
• Located in conjunction with a frontoparietal action
planning network:
– posterior inferior frontal
• pre-motor areas that represent impending actions
• Many cells are “motor dominant”: they fire when monkey grasps
or reaches, but are independent of visual input
– inferior parietal
• sensory area that integrates somatosensory, visual and
auditory signals
• Many cells are “visuo-dominant” or “visuomotor-dominant”: they
fire when monkey sees a graspable object or a stimulus that
could be interacted with
– These regions are densely interconnected
What are Mirror Neurons?
• Mirror neurons are in regions immediately adjacent to
these frontal and parietal areas
• Motor properties of mirror neurons are same as “nonmirror” neurons but…
• Sensory properties are different
– These cells do not fire when monkey sees a graspable
object
– They do fire when monkey sees another monkey (or a
person!) perform actions relative to objects
What can Mirror Neurons Represent?
• Some cells are precisely tuned to the specific actions
(strictly congruent – about 1/3 of cells)
– e.g. using two fingers to pick up an object
• Others are broadly tuned to any action that
accomplishes the same goal (broadly congruent –
about 2/3 of cells)
– E.g. using any combination of hand and fingers to pick up an
object
What can Mirror Neurons Represent?
• Mirror neurons represent abstract actions and goals
– Cells will not fire when grasping is pantomimed
– Cells will fire when grasping is real and visible
– Cells will also fire when grasping happens behind an
occluding screen, as long as the monkey has seen that there
is an object to be grasped behind the screen!
What can Mirror Neurons Represent?
• Mirror neurons represent abstract actions and goals
– Some mirror neurons will even fire in response to the sound
of an action being performed
• e.g. the sound of breaking a peanut shell
What are mirror neurons for?
• Two theories:
– Action imitation
– Understanding actions of others
Mirror Neurons in Humans?
• The existence of mirror neurons in humans is inferred
– We don’t record directly from human cortex!
Mirror Neurons in Humans?
• EEG and MEG evidence suggests a Mu
desynchronization (9 – 12 Hz over premotor areas)
when someone observes grasping
• TMS evidence shows that observed grasping
decreases the threshold for triggering motor
potentials for grasping muscles in the hand.
• The putative Mirror
Neuron System in
humans
Iacoboni et al (2006)
Mirror Neurons in Humans?
• fMRI studies have found evidence for two brain
regions associated with imitative actions
Task 1: watch action
Task 2: perform action
Task 3: imitate action
Mirror Neurons in Humans?
• Based on work with
monkeys, it was
presumed that mirror
neuron areas would
exhibit a specific pattern
of BOLD response:
• Task 1 < Task 2 < Task
3
• Two regions exhibited
such a response
Mirror Neurons Dysfunction in Autism?
• Some evidence supports a theory that a dysfunction
of the MNS underlies social isolation disorders such
as autism spectrum disorder (ASD)
– Some structural abnormalities
revealed with anatomical MRI
Mirror Neurons Dysfunction in Autism?
• fMRI data shows that BOLD signal in MNS
during viewing and imitating emotional
expressions is negatively correlated with
severity of Autism Spectrum Disorder
Mirror Neurons Dysfunction in Autism?
• Some evidence supports a theory that a dysfunction
of the MNS underlies social isolation disorders such
as autism spectrum disorder (ASD)
– MEG data shows abnormal propagation of signals
in the MNS when imitating lip movements in
individuals with Asperger’s Syndrome