Brain imaging the mirror neuron system
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Brain Imaging & the Mirror Neuron System. Lisa Aziz-Zadeh. Brain Imaging Methodologies. Fuctional Magnetic Resonance Imaging (fMRI) Transcranial Magnetic Stimulation (TMS). MRI and fMRI. MRI: Images of brain structure. fMRI: Images of brain function.

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Brain Imaging & the Mirror Neuron System

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Brain Imaging & the Mirror Neuron System

Lisa Aziz-Zadeh


Brain Imaging Methodologies

  • Fuctional Magnetic Resonance Imaging

    (fMRI)

  • Transcranial Magnetic Stimulation (TMS)


MRI and fMRI

  • MRI: Images of brain structure.

  • fMRI: Images of brain function.

  • Tissues differ in magnetic susceptibility (grey matter, white matter, cerebrospinal fluid)


Physiological basis for Blood Oxygen Level Dependent(BOLD) fMRI

  • Neural activity leads to increased blood flow.

  • Increased flow exceeds increased oxygen extraction, resulting in decreased deoxy-hemoglobin content.

  • Deoxyhemoglobin is paramagnetic, so reducing the deoxy-Hb/oxy-Hb ratio increases the signal.


FMRI signal and neural activity

  • Recently it hasbeen shown thatthe BOLD signalreliably reflectsneural activity(Logothetis et al., 2001).

  • BOLD signal was correlatedwith both local field potentials(reflecting input) and multi-unit activity (reflecting output)

  • Note the lag of the BOLDresponse relative to theneural activity.


Signal

Condition

Time

Acquiring functional images

  • Rapid sequence

  • Low resolution

  • Cognitivemanipulation

  • Statistics

TASKREST


Statistical parameter maps

  • Every voxel has associated statistics.

  • SPMs are superimposed on anatomical images, thresholded and clustered.


http://www.simplyphysics.com/MRIntro.html


Transcranial Magnetic Stimulation (TMS) as a Brain Mapping Tool


How TMS works

  • Pass a current through a hand held coil, whose shape determines the properties and the size of the field

  • The coil is driven by a machine which switches the large current necessary in a very precise and controlled way

  • The coil is held on the scalp and the magnetic field passes through the skull and into the brain

  • Small induced currents can then make brain areas below the coil more or less active, depending on the parameters used.


Safety Issues

  • Generally thought to be free from harmful effects

  • Examination of brain tissue submitted to thousands of TMS pulses has shown no detectable structural changes

  • It is possible in unusual circumstances to trigger a seizure in normal patients, but using the proper guidelines eliminate this risk


Different Types of TMS

  • Single Pulse

    • In the motor cortex, this usually causes a excitation in the brain.

  • rTMS

    • Multiple pulses in a short interval

    • Usually causes a “temporary lesion”


TMS as a Treatment Technique

  • Epilepsy

    • May be able to lower the number of seizures a patient

  • Depression

    • TMS treatments have been shown to cause improvement in severe cases of depression

    • An alternative to ECT


TMS as a tool in Research: Understanding the Motor System


TMS to understand the motor system

  • Understanding the motor system

    • Participants watch different things that we think may activate the motor system

    • If these stimuli do activate the motor system, the participant’s muscles are just beneath the threshold of movement

    • We record the muscle activity when we give TMS over the motor cortex

    • If the stimulus had an effect, then we see bigger muscle twitches than if the stimulus had no effect


TMS


Using TMS with fMRI

  • fMRI

    -uses amount of blood flow used by the brain to determine which areas are the most active (more active areas use more oxygen)


fMRI

  • Problem:

    • are the areas shown to be used in an fMRI image ESSENTIAL to the brain function, or are do they activate peripherally?

  • ROLE OF TMS:

    • Using the “inhibitory lesion technique” we can turn off the specific brain area and see if it is ESSENTIAL for the task. If the person can not perform the task during rTMS, it is essential.


The Mirror Neuron System


Mirror Neurons: Area F5


Cortical Mechanism forAction Recognition

adds additional somatosensory information to

the movement to be imitated

provides an early

description of the action

Observed

Action

STS

Parietal mirror neurons (PF)

(inferior parietal lobule)

Frontal mirror neurons (F5) (BA 44)

copies of the motor plans necessary to imitate actions for monitoring purposes

codes the goal of the

action to be imitated


Frontoparietal networks for action recognition


Expected Activity for Mirror Areas


A

B

C

Imitation of Hand Actions

Iacoboni et al. 1999


Iacoboni et al. 1999


Posterior Parietal Cortex

Execution

Observation

+

+

Iacoboni et al. 1999


Observation

Execution

Superior Temporal Sulcus and Imitation


Summary

  • Anatomical similarity between human and nonhuman primate frontoparietal mirror systems

  • Broca’s area codes the goal of the action (lift the finger)

  • PPC codes the precise kinesthetic aspects of the movement (how much the finger should be lifted)

  • STS codes the visual information (input)

  • Both left and right hemispheres are active


Acousitic Mirror Neurons


Auditory Mirror Neurons

peanut breaking

squeekingduck

vision & sound

100

spk/s

0

1s

vision

sound

motor

Christian Keysers


Acoustic Mirror Neurons in the Monkey: Kohler et al (2002)

  • Discriminated significantly between two different sounds of actions (ripping paper, breaking a peanut)

  • Representation of actions in these neurons are independent both of who performs the actions and how they are perceived

  • Multimodality may provide a first step towards abstract, semantic representations, perhaps tying to origin of language


Can we get a similar result in humans?

A study using TMS


Transcranial Magnetic Stimulation (TMS) Study

  • Q:

    • Do acoustic mirror neurons exist in the human brain?

    • Is there hemispheric specialization for the auditory modality?

  • Single pulse TMS to left or right primary motor (M1) hand area

  • Motor Evoked Potentials (MEPs) recorded from the left or right hand muscle (FDI)

  • Subject listens to 3 auditory stimuli:

    • Bimanual Hand Action Sound: Typing orTearing Paper

    • Bipedal Leg Action Sound: Walking

    • Control Sound: Thunder


Predicted Results

  • Prediction:

    • MEPs will be largest when the action sound matches the muscles of the stimulation site

    • Left hemisphere specialization


Results: Significant Facilitation to Hand Stimuli in the Left Hemisphere

*

*


Left Hemisphere MEP Means for a Sample Subject


Discussion

  • Motor facilitation to action sounds

  • Left hemisphere specialization

  • All the components of an action seem to be available to left hemisphere


Mirror Neurons and understanding another person’s INTENTIONS


  • Mirror neurons respond to GOAL ORIENTED actions, even when only the intent is apparent but the action itself is occluded

  • May have implications for INTENTION UNDERSTANDING

  • fMRI studies in Humans show similar findings (Iacoboni et al, 2004)


Mirror Neurons and Language

Language Evolution

Embodied Semantics


Language Evolution

  • Evolutionary progression from:

    • goal oriented actions

    • pantomiming without the goal present

    • abstracting the pantomime


Embodied Semantics


“She had the marvelous sensation of being a part of a vaster world and moving with it because of moving in rhythm with another being. The joy of this was so intense that when she saw him approaching she ran towards him wildly, joyously. Coming near him like a ballet dancer she took a leap towards him, and he, frightened by her vehemence and fearing that she would crash against him, instinctively became absolutely rigid, and she felt herself embracing a statue. Without hurt to her body, but with immeasurable hurt to her feelings.”

-Anais Nin, Stella


Embodied semantics

Hypothesis: The same brain area that processes sensory-motor experiences also processes the semantics related to that experience


“grasp the cup” = hand motor area

“kick the ball” = foot motor area

“I see what you mean” = visual area

“flew past me” = visual motion areas

“hear the music” = auditory areas


Action Observation Premotor Cortex

Buccino et al, 2001


Plan

  • Find regions of interest (ROIs) in the premotor cortex based on action observation of a given effector and compare that ROI with a participant reading a phrase with that same concept

    • Watch “grasping a cup” & Read “grasping a cup” = same brain area


Individual Subject ROI analysis: Observation

Left Hemisphere Right Hemisphere


Individual Subject ROI analysis:Literal Language

Left HemisphereRight Hemisphere


Discussion

  • Premotor areas that are activated most for observation of hand/mouth actions are also most activated for literal phrases pertaining to the hand/mouth

  • Left hemisphere specialization

  • Support for embodied semantics


“In all communication, sender and receiver must be bound by a common understanding about what counts; what counts for the receiver, else communication does not occur. Moreover the process of production and perception must somehow be linked; their representation must, at some point, be the same.”

-Alvin Liberman


Creation of Man

Michaelangelo


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