Handedness and hemispheric language dominance in healthy humans

Abstract

In most people the left hemisphere of the brain is dominant for language. Because of the increased incidence of atypical right-hemispheric language in left-handed neurological patients, a systematic association between handedness and dominance has long been suspected. To clarify the relationship between handedness and language dominance in healthy subjects, we measured lateralization directly by functional transcranial Doppler sonography in 326 healthy individuals using a word-generation task. The incidence of right-hemisphere language dominance was found to increase linearly with the degree of left-handedness, from 4% in strong right-handers (handedness = 100) to 15% in ambidextrous individuals and 27% in strong left-handers (handedness = -100). The relationship could be approximated by the formula: f1.gif" BORDER="0">. These results clearly demonstrate that the relationship between handedness and language dominance is not an artefact of cerebral pathology but a natural phenomenon.

Is digit ratio (2D:4D) a reliable pointer to speech laterality?

“…However, similar to [14], we did not find sex differences in speech laterality. If digit ratio is a reliable surrogate for pT the lack of a sex effect in speech representation would appear to be a challenge for androgen accounts of cerebral lateralisation.…”

“…A limitation of this approach is that handedness does not correlate perfectly to speech laterality. Although it is well known that for most humans the left-hemisphere is dominant for speech and handedness, some right-handers, and many ambilaterals and lefthanders have bilateral or right-hemisphere representation [14]. Moreover, handedness is multidimensional and there is no clear consensus on the precise components of handedness that may be related to speech representation.…”

Visual half-field experiments are a good measure of cerebral language dominance if used properly: Evidence from fMRI

“…Then, a subset of the participants took part in an fMRI based validation study. This study comprised the assessment of hemispheric dominance for language production, in a set-up employing a mental word generation task known to produce marked lateralization, in both fMRI and fTCD settings, which is in agreement with the lateralization determined by a Wada test (Knecht et al, 2000(Knecht et al, , 2001(Knecht et al, , 2003.…”

“…Knecht et al (2000) observed that in a student population up to 25% of strong left-handers have bilateral or right hemisphere dominant representation of their speech production, against a mere 5% of strong right-handers. It was a vital component of our study to be able to compare behavioral performance differences ranging from RVF advantage to LVF advantage with expected LH to RH dominance patterns obtained in the scanner.…”

Interhemispheric characterization of small vessel disease imaging markers after subcortical infarct

“…Our sample only comprised individuals presenting with symptoms. Broca's and Wernicke's speech areas are located in the left hemisphere for about 95% of right handers, but about 70% of left handers (Knecht et al., 2000). It is possible that the stroke could be less noticeable in the right hemisphere perhaps as the speech is less likely to be affected, thus indicating that maybe a percentage of RSSI that occur in the right hemisphere is disregarded and, therefore, unreported.…”