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Cortical asymmetries in the precuneus and fusiform gyri are associated with visual field
asymmetries in word processing: A voxel based analysis
Christiana M.
1
Leonard ,
Mark A.
2
Eckert ,
Suzanne E.
3
Welcome
& Christine
4
Chiarello
University of Florida1, Medical University of South Carolina2, University of Western Ontario3 University of California, Riverside4
Introduction
• A right visual field/left hemisphere (RVF/LH) advantage is routinely obtained in verbal
tasks where words are briefly presented to one or the other visual field. We predicted
that individual differences in the strength of this advantage would be associated with
individual differences in the asymmetry of Heschl’s gyrus, the planum temporale, pars
triangularis and the paracingulate sulcus. This hypothesis found little support in a study
that used manual measurements in a large sample of college students (Chiarello
2009).
• In the present study we used an automated whole brain analysis to revisit the
question of how structural asymmetries contribute to visual field asymmetries in
accuracy and reaction time.
Results
Summary
Brain regions with significant gray matter
asymmetry
• Three major clusters showed significant gray matter
asymmetry. In agreement with Watkins (2001), there were large
clusters of significantly asymmetric (L > R) voxels in the
superior temporal lobe/insula and occipital cortex (R > L).
There was also a L > R cluster in the cerebellum.
• All three asymmetry clusters can be seen in the figure on the
right. For display purposes, a threshold of t(198) = 24.0 (p
(FWE-corrected) < .0001) was used.
Method
Occipital
(R > L)
Cerebellum
L > R)
Heschl’s
gyrus/planum/insula (L
> R)
Regions with significant gray
matter asymmetry in 200
college students. Clusters are
thresholded at t (198) = 24.0
and displayed (MRIcron) on the
symmetrical study specific gray
matter template.
Brain regions where structural asymmetry was associated with a
RVF/LH advantage for reading words
PARTICIPANTS:
• 100 male (86 right handers), 100 female (88 right handers) native English
speakers, ranging in age from 18-34 years.
• Neither manual nor automated analyses identified any significant associations
between VF and perisylvian or paracingulate asymmetries.
PROCEDURES:
• Seven divided visual field tasks: lexical decision, masked word recognition, word
naming, nonword naming, semantic (manmade vs natural) decision, verb and
category generation.
IMAGE ANALYSIS:
• Two volumetric MRI scans (1.2 mm thick sagittal images) were collected from
each individual on a 1.5T GE Scanner. Scans were co-registered and averaged to
improve S/N.
• Native space and mirror image, flipped, images were segmented with SPM8
Unified Segmentation using ICBM a priori templates.
• Native space and flipped, segmented images were normalized into symmetrical
study-specific space using DARTEL (Ashburner 2007) .
• Normalized, modulated images were smoothed with an 8 mm kernel.
• Gray and white matter asymmetry images were created by subtracting each scan
from its mirror image (Watkins 2001).
• Reaction time asymmetry was associated with reciprocal gray and white matter
asymmetries in the fusiform VWFA and precuneus gyri, areas implicated in reading and
dyslexia (Maisog 2008) that have no known population asymmetry.
• Functional lateralization in VWFA for letters and words varies with the task and
contrast (Vigneau 2005; Graves 2009) but not visual field (Cohen 2002), possibly, due
to lateralized “top down” signals from language cortex (Ben Shachar 2007).
The results of the analyses were remarkably consistent in identifying the fusiform (3/4 regressions) and the
precuneus (4/4 regressions) gyri as regions where structural asymmetry was associated with behavioral (VF)
asymmetry. The values for fusiform and precuneus asymmetry were not correlated (r = .05, p NS).
Precuneus
• Cohen (2002) found that activation in the left precuneus but not the VWFA was
stronger to words presented in the RVF. They speculated that this activation “reflected
the attentional component of the RVF advantage”.
• The present results suggest that one factor contributing to the RVF/LH advantage for
reading words may be the asymmetrical development of fibers connecting nodes in a
lateralized reading network.
REFERENCES
STATISTICAL ANALYSIS:
• Asymmetry scores across the seven tasks were calculated separately for accuracy
and reaction time. Composite asymmetries were calculated by averaging the
individual z-scored task asymmetries. A positive asymmetry indicates faster RT and
greater accuracy for words presented in the right visual field.
Fusiform gyrus
Left hemisphere regions where
white matter asymmetry was
associated with faster reaction
times to words presented in the
right visual field (p < .001,
uncorrected). Clusters are
displayed on the symmetrical
white matter template.
• A one-sample t test was conducted to identify gray matter regions with significant
asymmetry in order to verify that processing the images with DARTEL produced
results similar to those of Watkins (2001).
• Four separate regression analyses examined the relation between composite
reaction time (CRTA) and accuracy asymmetries (CAA) and gray and white matter
asymmetries. T values for voxel clusters reported exceed p = 0.001, uncorrected.
The fusiform region overlaps with
the region called the “visual word
form area” (VWFA, Cohen 2002).
Fusiform gyrus
The values for peak gray matter asymmetry in
fusiform and precuneus were summed and plotted
against the composite RT asymmetry. There is a
modest positive relationship throughout the range.
Ashburner J. A fast diffeomorphic image registration algorithm. Neuroimage 2007; 38: 95-113.
Ben-Shachar M, Dougherty RF, Deutsch GK, Wandell BA. Differential sensitivity to words and
shapes in ventral occipito-temporal cortex. Cereb Cortex 2007;17:1604-11.
Cohen L, Lehericy S, Chochon F, Lemer C, Rivaud S, Dehaene S. Language-specific tuning of
visual cortex? Functional properties of the Visual Word Form Area. Brain. 2002;125:1054-69.
Chiarello C, Welcome SE, Halderman LK, Towler S, Julagay J, Otto R, Leonard CM. A large-scale
investigation of lateralization in cortical anatomy and word reading: are there sex differences?
Neuropsychology 2009; 23:210-22.-22.
Graves WW, Desai R, Humphries C, Seidenberg MS, Binder JR. Neural systems for reading aloud:
A multiparametric approach. Cereb Cortex 2009; 20:1799-815.
Maisog JM, Einbinder ER, Flowers DL, Turkeltaub PE, Eden GF. A meta-analysis of functional
neuroimaging studies of dyslexia. Ann N Y Acad Sci 2008; 1145: 237-59.
Vigneau M, Jobard G, Mazoyer B, Tzourio-Mazoyer N. Word and non-word reading: what role for
the Visual Word Form Area? Neuroimage. 2005; 27:694-705.
Watkins KE, Paus T, Lerch JP, Zijdenbos A, Collins DL, Neelin P, et al. Structural asymmetries in
the human brain: a voxel-based statistical analysis of 142 MRI scans. Cereb Cortex 2001; 11: 868-77.
ACKNOWLEDGMENTS
This research was supported by NIDCD grant 5R01DC6957 and the McKnight Brain Institute.