Meta-Analysis
Meta-analysis of Single Word Reading (PET)
Meta-analysis and fMRI Comparison
Meta-analysis for literature review
12 years of Single Word Reading Studies
Sources of Localization Variance
• Resolution limitations of technique • Different task parameters • Analysis
– smoothing – motion correction, normalization algorithms – differences in analysis between studies
• Inter-subject variability
Neuroimaging Meta-analysis
• Re-analysis of previous findings • Method of finding consistent activity
within the variance • Used to answer two questions:
– Is there a consistent difference between activation patterns for two tasks?
– What brain areas are consistently activated by a task?
Motor Areas of the Medial Wall Picard & Strick (1996)
Ant. Post.
29 studies
Visual Recognition of Words, Objects or Faces
Farah & Aguirre (1999)
“The only generalization that one can make… is that visual recognition is a function of the posterior half of the brain!”
20 studies
Single Word Reading Fiez and Petersen (1999)
Method: • 9 studies of overt single word reading • Differing control conditions • 147 foci of activation • Eliminate foci with neighbors (<20mm) from
fewer than half the studies • Assign remaining foci to 18 clusters • Find the mean location of each cluster
18 Clusters: L IFG, Motor cortex, SMA, Anterior Cingulate, STG, L Fusiform G, L Lingual G, thalamus, CB
Single Word Reading Fiez and Petersen (1999)
Meta-analysis Design Goals
• Maximize objectivity – Explicit inclusion criteria – Automated analysis technique
• Maximize quantification – Unbiased localization – Level of consistency – Statistical analysis of consistency
Hypotheses Which brain areas have been consistently activated during
neuroimaging studies of word reading?
Ho: Activation in previous studies is inconsistent (i.e. random)
H1: Activation in previous studies is consistent (i.e. nonrandom clustering)
Meta-analysis Data
• Task: Aloud Single Word Reading • Criteria
– healthy adult subjects – standardized coordinate space – most basal control condition available
• 11 studies • 16 contrasts • 172 foci
Included Studies
Foci of Activation
172 Foci from 11 Studies
Modeling Localization Variance
X
Gaussian Probability Distribution
FWHM=14.2mm
A 3-D Gaussian at (0,0,0)
Distributions can be summed
Methods
• Move all foci into the same coordinate space (MNI-space)
• Divide the space into 2mm cubic voxels • Model the localization probability
distribution for each focus using a 3-D Gaussian (FWHM = 14.2mm)
• For each voxel, find the union of the probability of localization for all foci
3-D Probability Density Map
The value at each voxel is the probability that at least one focus in the data-set actually occurs within that voxel.
Max = 1.5%
A
R L
P
The Null Hypothesis
• Ho= Localization of foci is random • represented by the 3-D probability
density map of a random data set • 1000 random sets of 172 foci were
analyzed • A histogram of probability values was
created
Probability Values for Ho
Prob = 5.535x10-3 Corrected p = .05
=Ho =Reading
noise
literature
Meta-Analysis Results
corrected p < .05
Turkeltaub et al. Neuroimage 16:765 (2002)
Meta-Analysis Results
Results Summary
Results Summary
Included Studies
Meta-analysis of Single Word Reading (PET)
Meta-analysis and fMRI Comparison
Meta-analysis for literature review
Problems Using fMRI in Language Studies
• Unintended auditory system stimulation
• Auditory stimulus masking
• Task interference
• Susceptibility artifacts from jaw movement
Data Acquisition Concurrent with Task
Data Acquisition
Task
Time
Hemodynamic Response
Hemodynamic Delay and Dispersion
Stimulus
Neuronal Response
Hemodynamic Response
Time
Data Acquisition After Task Completion
Data Acquisition
Task
Hemodynamic Response
Time
Behavior Interleaved Gradients
Task Epoch Control Epoch
task BIG
Conventional
gradients
fixate read delete
+ rat rat
rat at
fixation reading
+ vocalization
Task
Stimulus
Response
Processes
fixate (2 volumes)
DOG CAP HAT
rest 4 sec
read or delete (5 volumes)
BIG Image Data Acquisition
total of 62 volumes
+
task 9 sec
words fixation
19-34 group
- 38 - 42 - 46
- 50 - 54 - 58
Sound Deletion
• 15 adult subjects (10 female, 5 male) • aloud single word reading (high freq., 1 syllable) vs.
fixation • 80 whole-head EPI volumes per condition • BIG Technique • Data analysis: head motion correction, global
intensity normalization, high-pass temporal filtering, spatial smoothing, and spatial normalization to MNI-Talairach space
• Significance threshold set to match meta-analysis for number of significant voxels (Z score > 6.25)
fMRI Methods
Data Acquisition Details
• BOLD-contrast using EPI
• 1.5 T system • CP head coil • TR 13 sec • TE 40 ms • 3.0 mm3 voxels
fixate read
+ rat
rat
fixation reading
+ vocalization
Task
Stimulus
Response
Processes
Meta-Analysis vs. fMRI Meta-analysis fMRI
Left
Hem
R
ight
Hem
Meta-Analysis vs. fMRI Meta-Analysis fMRI Meta-Analysis fMRI
Turkeltaub et al. Neuroimage 16:765 (2002)
Central Drift Artifact Deep voxels are surrounded in all directions by potential contributors
Cortical voxels have fewer neighbors: lower likelihood of high probability scores
Deeper voxels =
Higher scores
Central Drift Artifact
z=0
Distance Between Loci
Probability value vs. Z score
Values at Closest Peaks
Summary
• Areas activated during single word reading: – Primary Motor Cortex – Superior Temporal Sulcus – L Fusiform Gyrus – Cerebellum – Thalamus – L Inferior Frontal Gyrus
• Meta-analysis results were good predictors of location and level of fMRI activation
• No Angular Gyrus activation
Turkeltaub et al. Neuroimage 16:765 (2002)
Meta-analysis of Single Word Reading (PET)
Meta-analysis and fMRI Comparison
Meta-analysis for literature review
PURE TONES
CATEGORIES
NOISE
MUSIC
VOCAL SOUNDS
-14 -8 -2 5 11 17
Samson et al., Frontiers in Auditory Cognitive Neuroscience (2010)
Samson et al., Frontiers in Auditory Cognitive Neuroscience (2010)
L R
VOCAL SOUNDS INTELLIGIBLE SPEECH
(B)
-14 -8 -2 5 11 17
(A)
(A)
(B)
CHANGING > UNCHANGING
MULTIPLE > SINGLE
(C)
-14 -8 -2 5 11 17
L R
Samson et al., Frontiers in Auditory Cognitive Neuroscience (2010)
Samson et al., Human Brain Mapping (2011)
Samson et al., Human Brain Mapping (2011)
Samson et al., Human Brain Mapping (2011)
Meta-analysis of Single Word Reading (PET)
Meta-analysis and fMRI Comparison
Meta-analysis for literature review