Poster C8, Wednesday, August 21, 2019, 10:45 am – 12:30 pm, Restaurant Hall
Atypical neural sources to speech-sound changes in dyslexia
Anja Thiede1, Lauri Parkkonen2, Paula Virtala1, Marja Laasonen3,4,5, Jyrki Mäkelä6, Teija Kujala1;1Cognitive Brain Research Unit, Faculty of Medicine, University of Helsinki, 2Department of Neuroscience and Biomedical Engineering, School of Science, Aalto University, 3Department of Psychology and Logopedics, Faculty of Medicine, University of Helsinki, 4Department of Phoniatrics, Helsinki University Hospital, 5Department of Psychology and Speech-Language Pathology, University of Turku, 6BioMag Laboratory, HUS Medical Imaging Center, Helsinki University Central Hospital
Developmental dyslexia has been associated with structural and functional brain abnormalities that may explain the reading impairment. One underlying deficit in dyslexia has been suggested to be of phonological nature, supported by mismatch negativity (MMN) studies showing neural speech processing impairments in readers with dyslexia. However, there is a lack of studies assessing the MMN sources in more detail in adult readers with dyslexia. So far, weakened mismatch fields (MMFs) to sound-frequency changes have been found in the left hemisphere of participants with dyslexia. We expected to find diminished MMFs in source space to speech-sound changes of a pseudoword in readers with dyslexia. We recorded magnetoencephalography (MEG) of 21 dyslexic and 22 non-dyslexic adult readers to a repeating pseudoword /tata/, the last syllable of which was occasionally replaced by a duration, frequency, or vowel change. During the MEG recordings, participants watched a silenced movie. Additionally, phonological processing, reading skills, intelligence quotient, and working memory were assessed with a neuropsychological test battery, and structural magnetic resonance images (MRI) of the brain were obtained to improve source localization. Data analysis was performed in MNE-Python software package. First, deviant–standard difference curves were calculated for each change type and participant, and averaged over groups. Then, source modeling was performed using a cortically-constrained source space based on individual MRIs. Weighted minimum-norm source estimates were obtained, morphed to an average brain template, and averaged for each group. To obtain MMF contrasts between groups, a spatio-temporal cluster permutation test was applied. Time courses extracted from the resulting clusters were compared post-hoc using one-way ANOVAs with group (control, dyslexia) as a between-subjects factor. Our results show that MMFs were elicited by all speech-sound changes in both groups. The groups differed in MMF source strengths. Preliminary results from the cluster permutation analysis suggest that readers with dyslexia had diminished MMF amplitudes to frequency changes in the right auditory cortex (all clusters p < 0.05). To duration and vowel changes, clusters were found in right fronto-parietal and frontal-pole areas. MMF amplitudes to duration changes were larger in participants with dyslexia compared to controls in the right fronto-parietal cortex (p < 0.05). MMF amplitudes to vowel changes were increased in participants with dyslexia in the frontal pole and diminished in a parietal area of the right hemisphere (both p < 0.05). These preliminary findings are consistent with previous studies showing sound-feature specific decreases or increases of MMN responses in dyslexia. Furthermore, they support the hypothesis of diminished MMF strengths in dyslexia for frequency changes, adding to previous EEG and MEG studies and reflecting impairments in processing speech-relevant auditory information in dyslexia.
Themes: Disorders: Developmental, Speech Perception
Method: Electrophysiology (MEG/EEG/ECOG)