what are mirror neurons? mirror neurons are cells that fire when a monkey (or person?) performs an...

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 “non-mirror” 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 actionsTask 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?

• 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

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