1. Mirror Neurons

2. 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

3. 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

4. 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

5. 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

6. 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!

7. 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

8. What are mirror neurons for?
Two theories:
Action imitation
Understanding actions of others

9. Mirror Neurons in Humans?
The existence of mirror neurons in humans is inferred
We don’t record directly from human cortex!

10. 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.

11. The putative Mirror Neuron System in humans
Iacoboni et al (2006)

12. 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

13. 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

14. 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

15. 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

16. 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