Brain Imaging

1
Brain Imaging the Mirror Neuron System

• Lisa Aziz-Zadeh

2
Brain Imaging Methodologies

• Fuctional Magnetic Resonance Imaging
• (fMRI)
• Transcranial Magnetic Stimulation (TMS)

3
MRI and fMRI

• MRI Images of brain structure.
• fMRI Images of brain function.
• Tissues differ in magnetic susceptibility (grey
  matter, white matter, cerebrospinal fluid)

4
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.

5
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.

6
Acquiring functional images

• Low resolution

• Rapid sequence

• Cognitivemanipulation

• Statistics

TASK REST
7
Statistical parameter maps

• Every voxel has associated statistics.
• SPMs are superimposed on anatomical images,
  thresholded and clustered.

8
http//www.simplyphysics.com/MRIntro.html
9
Transcranial Magnetic Stimulation (TMS) as a
Brain Mapping Tool
10
(No Transcript)
11
(No Transcript)
12
(No Transcript)
13
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.

14
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

15
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

16
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

17
TMS as a tool in Research Understanding the
Motor System

18
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 participants 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

19
TMS
20
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)

21
(No Transcript)
22
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.

23
(No Transcript)
24
The Mirror Neuron System
25
(No Transcript)
26
Mirror Neurons Area F5
27
(No Transcript)
28
(No Transcript)
29
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
30
Frontoparietal networks for action recognition
31
(No Transcript)
32
Expected Activity for Mirror Areas
33
Imitation of Hand Actions
Iacoboni et al. 1999
34
Iacoboni et al. 1999
35
Posterior Parietal Cortex
Execution
Observation


Iacoboni et al. 1999
36
Superior Temporal Sulcus and Imitation
37
Summary

• Anatomical similarity between human and nonhuman
  primate frontoparietal mirror systems
• Brocas 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

38
Acousitic Mirror Neurons
39
Auditory Mirror Neurons
Christian Keysers
40
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

41
Can we get a similar result in humans?

• A study using TMS

42
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

43
Predicted Results

• Prediction
• MEPs will be largest when the action sound
  matches the muscles of the stimulation site
• Left hemisphere specialization

44
Results Significant Facilitation to Hand Stimuli
in the Left Hemisphere


45
Left Hemisphere MEP Means for a Sample Subject
46
Discussion

• Motor facilitation to action sounds
• Left hemisphere specialization
• All the components of an action seem to be
  available to left hemisphere

47
Mirror Neurons and understanding another persons
INTENTIONS
48

• 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)

49
Mirror Neurons and Language

1. Language Evolution
2. Embodied Semantics

50
(No Transcript)
51
Language Evolution

• Evolutionary progression from
• goal oriented actions
• pantomiming without the goal present
• abstracting the pantomime

52
Embodied Semantics
53
(No Transcript)
54

• 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

55
Embodied semantics

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

56
(No Transcript)
57

• 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

58
Action Observation Premotor Cortex
Buccino et al, 2001
59
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

60
(No Transcript)
61
Individual Subject ROI analysis Observation
Left Hemisphere Right Hemisphere
62
Individual Subject ROI analysisLiteral Language
Left Hemisphere Right Hemisphere
63
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

64

• 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

65
Creation of Man Michaelangelo