Oral and written narrative comprehension in left-brain damaged individuals and brain volumes correlates

• ¹ Pontifícia Universidade Católica do Rio Grande do Sul, Linguistics, Brazil
• ² University of Helsinki, Finland
• ³ Pontifícia Universidade Católica do Rio Grande do Sul, Engineering, Brazil
• ⁴ Pontifícia Universidade Católica do Rio Grande do Sul, Medicine School, Brazil
• ⁵ Pontifícia Universidade Católica do Rio Grande do Sul, Gerotology and Geriatrics Institut, Brazil
• ⁶ Universidade Estadual do Rio Grande do Sul, Brain Institute - InsCer, Brazil

Introduction: Research with left-brain damaged (LBD) participants suggests they present difficulties in comprehending words and sentences (Ortiz, 2010). Little is known about the influence of a lesion at the textual/discursive level, including comparisons between oral and written presentation modalities. It seems that LBD participants lack comprehension mainly at macrolinguistic structures (Karaduman, Göksun & Chatterjee, 2017). In addition, brain areas from frontal, temporal and parietal lobes of both hemispheres seem to be involved in the text comprehension (Babajani-Feremi, 2017; Barbey; Colom & Grafman, 2014). However, more conclusive data are necessary correlating behavioral and brain evidence in discourse processing in left brain lesion. Aim: to analyze comprehension of written and orally presented short narratives by LBD participants compared to controls in their performance at the micro- and macrolinguistic levels, and the correlated brain volumes in the areas involved in this type of processing. Method: Participants: 10 LBD participants (mean age 66,4, SD = 8,89, 1 F/ mean schooling 7,4 y/SD = 3,56), and 10 matched healthy controls (mean age 66,3, SD = 8,73, 9 F/ mean schooling 6,9 y/SD = 3,92). Instruments and procedures: Subjects were asked to retell in details six short narratives, presented in oral or written modalities. Following, they answered to five interpretation questions. Structural MRI sessions were used to collect brain volume data using voxel-based morphometry (VBM). Results: Controls showed significantly higher performance than LBD participants at the macrolinguistic level of oral narratives (p=0,04) as compared to written ones. This finding suggests LBD participants have difficulties in the application of macrolinguistic rules of deletion, construction and generalization to understand macrolinguistic structure of a text, with increased difficulty in dealing with the written modality. Morphometry data of brain regions indicated an integration of areas in the left and right hemispheres to perform text comprehension in oral and written modalities. In the left hemisphere, density variations were observed in precuneus, cerebellum white matter, superior frontal region and medial orbitofrontal region, while in the right hemisphere variations were seen in the accumbens and superior temporal sulcus. Density increase in the right superior temporal sulcus, left precuneus, left cerebellar white matter and superior frontal region positively correlate with higher performance. The left medial orbitofrontal region shows a negative correlation with performance. The right accumbens seems to compensate left hemisphere demands, showing increased density in the LBD participants and reduced volume in controls. Conclusions: Significant differences were observed in groups’ comparisons at the macrolinguistic level of oral texts. Although modalities differed, significant lower performance was observed only in the oral modality by the LBD group as compared to controls. Analysis of VBM demonstrated that a variation in density of different left and right hemisphere areas relates to performance in text comprehension. More specifically, the volume of left hemisphere regions such as precuneus, superior temporal sulcus, superior frontal, medial orbitofrontal areas and cerebellum white matter, and right hemisphere areas at the accumbens and superior temporal sulcus may impact LDB individual’s text comprehension.