Transcript Lecture 27 Powerpoint File

Mirror Neurons
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
– e.g. using two fingers to pick up an object
• Others are broadly tuned to any action that
accomplishes the same goal
– 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 can Mirror Neurons Represent?
• Mirror neurons represent intended actions
– Some cells fire more when monkey grasps food
with intention to eat it – or when monkey
observes a human grasping food to eat it
– Some cells fire more when monkey grasps food
with intention to place it in a container – or when
monkey observes a human placing food in a
container
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?
• 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 in Humans?
• Mirror Neuron System (MNS) in Humans seems to be part of a
system that mediates empathy
• fMRI data revealed MNS areas plus limbic areas became
activated during observation of emotional faces
– MNS areas became more activated during imitation of an emotional
facial expression
Mirror Neurons Dysfunction in
Autism?
• Some evidence supports a theory (speculation?) that a
dysfunction of the MNS underlies social isolation disorders
such as autism spectrum disorder (ASD)
– Some structural abnormalities
– MEG data shows abnormal propagation of signals in the MNS when imitating lip
movements in individuals with Asperger’s Syndrome
– fMRI data shows that BOLD signal in MNS during viewing and imitating emotional
expressions is negatively correlated with severity of Autism Spectrum Disorder