Language production vs. perception in patients with congenital damage to the left hemisphere

Introduction Children with congenital left hemispheric (LH) brain damage do usually not have language disturbances. It is well established that language may be represented in the right instead of the left hemisphere in these children, recruiting areas homotopic to the classical language regions. Language perception and production recruit dissociable LH networks in the brain, perception being more bilateral. As studies comparing language perception and production with respect to their representation in LH lesioned brains provide conflicting results, we used a productive and a perceptive language paradigm in the same group of patients with congenital LH brain lesions to explore the factors contributing to reorganization of productive and perceptive language functions. Methods Nine Patients (4 male, 8 to 31yr) with pre- or perinatal lesions of the LH were compared to nine healthy right-handers (5 male, 11 to 32 yr. All subjects were native speakers of German, and groups did not differ significantly in verbal IQ (according to the German WISC/WAIS). All subjects were confronted with the Vowel-identification task (VI; Language Production; Wilke et al., 2006) and the Beep Stories task (BS; Language Perception; Wilke et al., 2005). Data was preprocessed and analyzed using SPM5. Results The VI task activated the inferior and middle frontal gyrus in both groups. Activation, however, was seen only in the left hemisphere in the control group and only in the right hemisphere in the patient group. The BS task strongly activated both superior temporal gyri and both inferior frontal gyri in the control group, and the right superior temporal gyrus in the patient group. Lateralization was strongly leftwards in the control group and strongly rightwards in the patient group (Figure1). While the control group had a mean lateralization to the left side for both paradigms (VI: mean= −.75, SD= .1; BS: mean= −.28, SD= .3), in the patient group no clear lateralization effect was found (VI: mean= .17, SD= .4; BS: .17, SD= .53). Variability was stronger in the patient than in the control group in both paradigms as is indicated by larger standard deviations. In the control group, the two paradigms differed in the strength of lateralization: The productive VI task was strongly lateralized in most subjects, while the perceptive BS task demonstrated a considerable variability between subjects and overall less lateralization. In the patient group this paradigm effect was not observable: Variability was considerable in both paradigms, and both paradigms showed a medium degree of lateralization. Productive and perceptive lateralization did not correlate (r= .352; p= .353). Analysis of lesion types revealed a differential effect: Damage to the temporal lobe influenced the lateralization of language perception, but not production. [Figure 2 Center] Conclusions Language production and perception may be hemispherically dissociated in patients with congenital LH brain lesions. While even small lesions of the facial motor tract can trigger reorganization of language production in patients with intact language cortex (Staudt et al., 2008), lesions or malformations of the temporal lobe seem to induce reorganization of language perception