Age-related language lateralization assessed by fMRI: The effects of sex and handedness.

Previous studies focusing on the relationship between lateralization of language function and age suffer from lack of a balanced distribution of age and handedness among participants, especially in the extremes of age. This limits our understanding of the influence of these factors on lateralization of language circuitry. The hemispheric asymmetry reduction in older adults (HAROLD) model suggests that under similar circumstances, involvement in cognitive processes of prefrontal (and potentially other) cortical areas tends to be less lateralized with age. In this study, we aimed to investigate the link between age, gender, and language lateralization in a large group of healthy participants with a relatively even distribution of age and handedness in order to further test the HAROLD model. 99 healthy men (33 left-handed; age range 18-74years) and 125 women (44 left-handed; age range 19-76) were recruited. All participants underwent fMRI at 3T with a semantic decision and a verb generation tasks and received a battery of linguistic tests. Lateralization indexes (LI) were calculated for each participant based on fMRI results for each task separately. LIs were found to be significantly decreasing with age only in right-handed men and only in temporo-parietal cortical area. LIs did not change with age in other brain regions or in left-handed subjects. Our results do not support the HAROLD model and suggest a potentially different relationship between aging and lateralization of language functions.