Language lateralization in healthy right-handers

Abstract

Our knowledge about the variability of cerebral language lateralization is derived from studies of patients with brain lesions and thus possible secondary reorganization of cerebral functions. In healthy right-handed subjects 'atypical', i.e. right hemisphere language dominance, has generally been assumed to be exceedingly rare. To test this assumption we measured language lateralization in 188 healthy subjects with moderate and strong right-handedness (59% females) by a new non-invasive, quantitative technique previously validated by direct comparison with the intracarotid amobarbital procedure. During a word generation task the averaged hemispheric perfusion differences within the territories of the middle cerebral arteries were determined. (i) The natural distribution of language lateralization was found to occur along a bimodal continuum. (ii) Lateralization was equivalent in men and women. (iii) Right hemisphere dominance was found in 7.5% of subjects. These findings indicate that atypical language dominance in healthy right-handed subjects of either sex is considerably more common than previously suspected.

Alpha activity in the insula accompanies the urge to neutralize in sub-clinical obsessive-compulsive participants

“…The left hemispheric lateralization of greater alpha activity in the insula/vlPFC during negative compared to positive visualisation is unlikely to be specifically associated with feelings of urge or craving per se, as previous studies have not suggested lateralization of these processes (Naqvi & Bechara, 2008;Naqvi, Rudrauf, Damasio & Bechara, 2007). A more apposite explanation is that the observed left lateralization is related to language processing, for which the left hemisphere is dominant (Knecht et al, 2000), and the participants' conscious experience of their urge to neutralize. The forms of cognitive reappraisal which were endorsed by participants are likely to have involved sub-vocalisation, which is consistent with the role of left lateralized insula, and particularly vlPFC, in 'inner speech' (Morin, 2009;Riecker, Ackermann, Wildgruber, Dogil & Grodd, 2000) which appears to be crucial to the experience of self-conscious emotions (Jones & Fernyhough, 2007;Morin, 2009;Morin & Michaud, 2007).…”

The evolution and genetics of cerebral asymmetry

“…There is also a weak correlation between handedness and the lateralized representation of language in the human brain. Studies based on the Wada test (Rasmussen & Milner 1977), electroconvulsive therapy (Warrington & Pratt 1973) and brain imaging (Pujol et al 1999;Knecht et al 2000) are reasonably consistent in showing that over 90 per cent of right-handers are left-cerebrally dominant for language, compared with approximately 70 per cent of left-handers. These estimates can be matched by McManus's model with p(D)Z0.8, on the assumption that handedness and cerebral dominance for language are subject to the same biases in the three genotypes, but that the biases are applied independently (table 2).…”

Comparative and familial analysis of handedness in great apes.

“…Right handedness presumably reflects a left-hemisphere specialization for motor skills and is thought to be an indirect marker of lateralization for language functions. For example, 96% of righthanded individuals are left-hemisphere dominant for language in contrast to about 70% in lefthanded individuals (Knecht et al, 2000;Rasmussen & Milner, 1977). The association between hand preference and language dominance has led to a number of evolutionary and biological theories proposing that hemispheric specialization and language (or perhaps other higher cognitive functions) coevolved and are unique characteristics of the human brain (see Annett, 1985;Corballis, 1992Corballis, ,2002Crow, 1998;Yeo, Thoma, & Gangestad, 2002, for reviews).…”