Language lateralization in left-handed and ambidextrous people: fMRI data.
BACKGROUND
It is generally accepted that most people have left-hemispheric language dominance, though the actual incidence of atypical language distribution in non-right-handed subjects has not been extensively studied. The authors examined language distribution in these subjects and evaluated the relationships between personal handedness, family history of sinistrality, and a language laterality index (LI) measured with fMRI.


METHODS
The authors used whole-brain fMRI to examine 50 healthy, non-right-handed subjects (Edinburgh Handedness Inventory quotient between -100 and 52) while they performed language activation and nonlinguistic control tasks. Counts of active voxels (p < 0.001) were computed in 22 regions of interest (ROI) covering both hemispheres and the cerebellum. LI were calculated for each ROI and each entire hemisphere using the formula [L - R]/[L + R].


RESULTS
Activation was predominantly right hemispheric in 8% (4/50), symmetric in 14% (7/50), and predominantly left hemispheric in 78% (39/50) of the subjects. Lateralization patterns were similar for all hemispheric ROI. Associations were observed between personal handedness and LI (r = 0.28, p = 0.046), family history of sinistrality and LI (p = 0.031), and age and LI (r = -0.49, p < 0.001).


CONCLUSIONS
The incidence of atypical language lateralization in normal left-handed and ambidextrous subjects is higher than in normal right-handed subjects (22% vs 4-6%). These whole-brain results confirm previous findings in a left-handed cohort studied with fMRI of the lateral frontal lobe. Associations observed between personal handedness and LI and family history of handedness and LI may indicate a common genetic factor underlying the inheritance of handedness and language lateralization.
Department of Neurology, University of Cincinnati Medical Center, Cincinnati, OH 45267, USA. Jerzy.Szaflarski@uc.edu
J P
JP
Szaflarski
J R
JR
Binder
E T
ET
Possing
K A
KA
McKiernan
B D
BD
Ward
T A
TA
Hammeke
D000328:Adult; D000375:Aging; D001931:Brain Mapping; D005260:Female; D007839:Functional Laterality / Q000235:genetics; D006801:Humans; D007802:Language; D016014:Linear Models; D008279:Magnetic Resonance Imaging; D008297:Male; D011597:Psychomotor Performance; D012016:Reference Values