Sex differences in neural processing of language among children

Abstract

Why females generally perform better on language tasks than males is unknown. Sex differences were here identified in children (ages 9-15) across two linguistic tasks for words presented in two modalities. Bilateral activation in the inferior frontal and superior temporal gyri and activation in the left fusiform gyrus of girls was greater than in boys. Activation in the left inferior frontal and fusiform regions of girls was also correlated with linguistic accuracy irregardless of stimulus modality, whereas correlation with performance accuracy in boys depended on the modality of word presentation (either in visual or auditory association cortex). This pattern suggests that girls rely on a supramodal language network, whereas boys process visual and auditory words differently. Activation in the left fusiform region was additionally correlated with performance on standardized language tests in which girls performed better, additional evidence of its role in early sex differences for language.

Figure 1

Activation and sex differences during language tasks. Activation across both language judgment tasks and sensory modalities was elicited across all age groups irrespective of sex (yellow in brain images), but girls (pink) showed significantly greater activation than boys (blue) in bilateral regions of IFG and STG as well as left FG. Task, modality, age, and sex were entered into an ANCOVA model with accuracy as a covariate. Graph data were derived from ROI analysis of five regions showing significant sex effects (p < 0.005 with a Bonferroni correction); the BOLD signal represents the estimated partial means derived from the mean activity of each region of interest after removing variance attributable to age and accuracy.

Figure 2

Sex differences in laterality reflect a threshold effect. Using a more stringent statistical threshold (p = 1.0 × 10⁻⁷ with a FDR correction), the left hemisphere showed similar patterns of activation by boys (blue) and girls (pink), including substantial overlap (cyan), but only girls showed bilateral activation in IFG and STG. IFG = inferior frontal gyrus, STG = superior temporal gyrus, FG = fusiform gyrus, ITG = inferior temporal gyrus, Cun = cuneus, Ling = lingual gyrus.

Figure 3

Activation during nonlinguistic sensory tasks and sex effects. A, activation by nonlinguistic visual stimuli showed greater activation by girls (pink) in fusiform gyrus (FG); boys did not show greater activation anywhere. B, activation by nonlinguistic auditory stimuli showed greater activation by girls in superior temporal gyrus. STG = superior temporal gyrus, FG = fusiform gyrus.

Figure 4

Sex differences in correlation of activation with performance accuracy grouped by judgment task and by modality. A, after accounting for differences in responses to words presented in each sensory modality, activation in MTG / FG and IFG was correlated with performance accuracy on both rhyming and spelling tasks among girls (pink) but not boys. B, after accounting for differences in responses to different language judgments, activation by auditory word stimuli among boys (blue) was correlated with performance accuracy in STG and IFG, whereas activation by visual word stimuli was correlated with performance accuracy in SPL / PreCun. Among girls (pink), correlation of accuracy with activation for auditory word stimuli was generally distinct from regions correlated with accuracy among boys, although overlap (cyan) was evident in IFG and (slightly) in posterior MTG. Activation by visual word stimuli was not correlated with performance accuracy irrespective of language judgment among girls. IFG = inferior frontal gyrus, MTG / FG = middle temporal gyrus extending into fusiform gyrus, SPL / PreCun = superior parietal lobule extending into precuneus.