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A reduction or reversal of the normal leftward asymmetry of the planum temporale (PT) has been claimed to be typical of dyslexia, although some recent studies have challenged this view. In a population-based study of 20 right-handed dyslexic boys and 20 matched controls, we have measured the PT and the adjacent planum parietale (PP) region in sagittal magnetic resonance images. For the PT, mean left and right areas and asymmetry coefficients were compared. Since a PP area often could not be identified in one or both hemispheres, a qualitative comparison was used for this region. The total planar area (sum of PT and PP) was also compared between the two groups. A dichotic listening (DL) test with consonant-vowel syllables was administered to assess functional asymmetry of language. The results showed a mean leftward PT asymmetry in both the dyslexic and the control group, with no significant difference for the degree of PT asymmetry. Planned comparisons revealed however, a trend towards smaller left PT in the dyslexic group. In control children, but not in the dyslexic children, a significant correlation between PT asymmetry and reading was observed. A mean leftward asymmetry was also found for the total planar area, with no difference between the groups for the degree of asymmetry. Significantly fewer dyslexic children than control children showed a rightward asymmetry for the PP region. Both groups showed a normal right ear advantage on the DL task, with no significant difference for DL asymmetry. No significant correlation was observed between PT asymmetry and DL asymmetry. The present population-based study adds to recent reports of normal PT asymmetry in dyslexia, but indicates that subtle morphological abnormalities in the left planar area may be present in this condition.
E Heiervang, and
K Hugdahl, and
H Steinmetz, and
A Inge Smievoll, and
J Stevenson, and
A Lund, and
L Ersland, and
A Lundervold
January 2002,
Journal of the International Neuropsychological Society : JINS,
E Heiervang, and
K Hugdahl, and
H Steinmetz, and
A Inge Smievoll, and
J Stevenson, and
A Lund, and
L Ersland, and
A Lundervold
April 2002,
Archives of neurology,
E Heiervang, and
K Hugdahl, and
H Steinmetz, and
A Inge Smievoll, and
J Stevenson, and
A Lund, and
L Ersland, and
A Lundervold
January 2000,
Mental retardation and developmental disabilities research reviews,
E Heiervang, and
K Hugdahl, and
H Steinmetz, and
A Inge Smievoll, and
J Stevenson, and
A Lund, and
L Ersland, and
A Lundervold
November 2005,
The anatomical record. Part A, Discoveries in molecular, cellular, and evolutionary biology,
E Heiervang, and
K Hugdahl, and
H Steinmetz, and
A Inge Smievoll, and
J Stevenson, and
A Lund, and
L Ersland, and
A Lundervold
August 2013,
Neuropsychologia,
E Heiervang, and
K Hugdahl, and
H Steinmetz, and
A Inge Smievoll, and
J Stevenson, and
A Lund, and
L Ersland, and
A Lundervold
June 1998,
Neuropsychology review,
E Heiervang, and
K Hugdahl, and
H Steinmetz, and
A Inge Smievoll, and
J Stevenson, and
A Lund, and
L Ersland, and
A Lundervold
December 2014,
Human brain mapping,
E Heiervang, and
K Hugdahl, and
H Steinmetz, and
A Inge Smievoll, and
J Stevenson, and
A Lund, and
L Ersland, and
A Lundervold
February 2008,
Dyslexia (Chichester, England),
E Heiervang, and
K Hugdahl, and
H Steinmetz, and
A Inge Smievoll, and
J Stevenson, and
A Lund, and
L Ersland, and
A Lundervold
August 1999,
Journal of clinical and experimental neuropsychology,
E Heiervang, and
K Hugdahl, and
H Steinmetz, and
A Inge Smievoll, and
J Stevenson, and
A Lund, and
L Ersland, and
A Lundervold
February 2008,
Dyslexia (Chichester, England),
