Growing up with one ear : central auditory structure and function in unilateral ear canal atresia
Author: Siegbahn, Malin
Date: 2023-11-24
Location: Birke 1, F52, Karolinska University Hospital, Huddinge
Time: 09.00
Department: Inst för klinisk vetenskap, intervention och teknik / Dept of Clinical Science, Intervention and Technology
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Thesis (1.090Mb)
Abstract
The following thesis aims to give more insight into the functional and structural response of the central auditory system to congenital unilateral ear canal atresia (UCA) and the accompanying asymmetric hearing with conductive hearing loss on the atretic side.
There is clear evidence that unilateral hearing loss, including UCA, has a negative impact on sound localization ability and perception of speech in noise. There is a spread in performance within the group, and the reason for this is not well known. In paper I of this thesis we examined sound localization with eye tracking and perception of speech in a cocktail party setting, in participants with congenital unilateral ear canal atresia, who had no hearing aids before age 12 (n=12) and compared to normal hearing references. Results show that the level of hearing loss on the atretic ear was associated with sound localization ability but not to speech perception.
In the second study, participants with UCA (n=17) underwent MRI-scanning of the brain with diffusion weighted imaging (DWI). A method is described how to segment the white matter bundle between the medial geniculate body of the thalamus and the primary auditory cortex, the acoustic radiation (AR). Methods to define the AR are previously described in high resolution diffusion weighted imaging (DWI) scans but is very time consuming or has problems with including more structures around the primary auditory cortex (PAC). An algorithm was trained to quickly segment the core of the AR in individual clinical scans. The white matter tract was also assessed with measurements of fractional anisotropy (FA), but no differences were found between UCA and normal hearing (NH) controls.
The third study describes the measurements of the grey matter of the primary auditory cortex of the Heschl’s gyrus in the same participants as in paper II. Thickness and volume of the Heschl’s gyrus were compared within the groups of UCA and controls, and between the groups. A difference in thickness was found between the left and right side (right thicker than left, corrected p=0.0012) in UCA, whereas controls had symmetric thickness. Volumes and total thickness were not different compared to controls.
Rat brains from 12 months old rats with a surgically constructed left-sided ear canal atresia were examined in study IV. DWI was acquired in a research camera for rodents, 9.4 T magnetic field and a prolonged scanning time. Tractography and FA measurements were obtained both from whole brains and from tracts between auditory regions of interest (ROIs) using two different software. FA was generally higher in UCA rats than in controls. The AR was asymmetric in FA (left<right) in UCA, whereas FA was symmetric in controls. The FA was found to be lower at the left connection (same side as hearing loss) cochlear nucleus -inferior colliculus compared to the right side in UCA, while it was symmetric in controls. This finding (CN-IC) aligns with previous histology findings in ferrets with unilateral conductive hearing loss.
There is clear evidence that unilateral hearing loss, including UCA, has a negative impact on sound localization ability and perception of speech in noise. There is a spread in performance within the group, and the reason for this is not well known. In paper I of this thesis we examined sound localization with eye tracking and perception of speech in a cocktail party setting, in participants with congenital unilateral ear canal atresia, who had no hearing aids before age 12 (n=12) and compared to normal hearing references. Results show that the level of hearing loss on the atretic ear was associated with sound localization ability but not to speech perception.
In the second study, participants with UCA (n=17) underwent MRI-scanning of the brain with diffusion weighted imaging (DWI). A method is described how to segment the white matter bundle between the medial geniculate body of the thalamus and the primary auditory cortex, the acoustic radiation (AR). Methods to define the AR are previously described in high resolution diffusion weighted imaging (DWI) scans but is very time consuming or has problems with including more structures around the primary auditory cortex (PAC). An algorithm was trained to quickly segment the core of the AR in individual clinical scans. The white matter tract was also assessed with measurements of fractional anisotropy (FA), but no differences were found between UCA and normal hearing (NH) controls.
The third study describes the measurements of the grey matter of the primary auditory cortex of the Heschl’s gyrus in the same participants as in paper II. Thickness and volume of the Heschl’s gyrus were compared within the groups of UCA and controls, and between the groups. A difference in thickness was found between the left and right side (right thicker than left, corrected p=0.0012) in UCA, whereas controls had symmetric thickness. Volumes and total thickness were not different compared to controls.
Rat brains from 12 months old rats with a surgically constructed left-sided ear canal atresia were examined in study IV. DWI was acquired in a research camera for rodents, 9.4 T magnetic field and a prolonged scanning time. Tractography and FA measurements were obtained both from whole brains and from tracts between auditory regions of interest (ROIs) using two different software. FA was generally higher in UCA rats than in controls. The AR was asymmetric in FA (left<right) in UCA, whereas FA was symmetric in controls. The FA was found to be lower at the left connection (same side as hearing loss) cochlear nucleus -inferior colliculus compared to the right side in UCA, while it was symmetric in controls. This finding (CN-IC) aligns with previous histology findings in ferrets with unilateral conductive hearing loss.
List of papers:
I. Siegbahn M, Engmér Berglin C, Hultcrantz M, Asp F. (2021). Adults with unilateral congenital ear canal atresia -sound localization ability and speech in competing speech in unaided condition. Acta Otolaryngol. 2021 Jul;141(7):689-694.
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II. Siegbahn M, Engmér Berglin C, Moreno R. (2022). Automatic segmentation of the core of the acoustic radiation in humans. Front Neurol. 2022 Sep 23, 13: 934650.
Fulltext (DOI)
Pubmed
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III. Siegbahn M, Jörgens D, Aspp F, Hultcrantz M, Moreno R, Engmér Berglin C. Asymmetry in cortical thickness of the Heschl’s gyrus in unilateral ear canal atresia. Otology & Neurotology. [Accepted]
IV. Siegbahn M, Kraft S, Maschio F, Hultcrantz M, Engmér Berglin C, Moreno R. White matter tracts of the auditory pathways in experimental unilateral ear canal atresia. [Manuscript]
I. Siegbahn M, Engmér Berglin C, Hultcrantz M, Asp F. (2021). Adults with unilateral congenital ear canal atresia -sound localization ability and speech in competing speech in unaided condition. Acta Otolaryngol. 2021 Jul;141(7):689-694.
Fulltext (DOI)
Pubmed
View record in Web of Science®
II. Siegbahn M, Engmér Berglin C, Moreno R. (2022). Automatic segmentation of the core of the acoustic radiation in humans. Front Neurol. 2022 Sep 23, 13: 934650.
Fulltext (DOI)
Pubmed
View record in Web of Science®
III. Siegbahn M, Jörgens D, Aspp F, Hultcrantz M, Moreno R, Engmér Berglin C. Asymmetry in cortical thickness of the Heschl’s gyrus in unilateral ear canal atresia. Otology & Neurotology. [Accepted]
IV. Siegbahn M, Kraft S, Maschio F, Hultcrantz M, Engmér Berglin C, Moreno R. White matter tracts of the auditory pathways in experimental unilateral ear canal atresia. [Manuscript]
Institution: Karolinska Institutet
Supervisor: Engmér Berglin, Cecilia
Co-supervisor: Moreno, Rodrigo; Asp, Filip
Issue date: 2023-10-17
Rights:
Publication year: 2023
ISBN: 978-91-8017-100-7
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