With the establishment of newborn hearing screening programs to evaluate hearing status at birth, the number of infants identified with UHL is on the rise and the need to understand the impact of UHL in children has gained recent attention.22
In this pilot study, we have begun to investigate whether patterns of functional connectivity associated with central auditory processes and executive function in children with UHL differ from NH siblings using rs-fcMRI. Resting state fcMRI measures offer the advantage of independence from task protocols, so results are not dependent on subjects' attention or performance. These methods also carry the promise of demonstrating how the brain's functional architecture, as revealed by functional connectivity, is modified in the presence of UHL.10
The results of this pilot study show that rs-fcMRI can identify differences in the brain's functional network architecture when comparing children with UHL and children with NH. Because the degree to which UHL might alter auditory processing networks is unknown, we chose to examine children with severe-to-profound UHL rather than those with less severe UHL. We found differences between children with UHL and NH in multiple networks. The left IPL seed, the only seed to show consistent mean regionwise t-test differences between controls and both UHL groups in this study, is a fronto-parietal region (trial level control) involved in sustained task set maintenance activity.8
The posterior operculum region, which is more correlated to left IPL in UHL subjects than controls, is close to a region found by Julie Fiez and colleagues to be related to echoic memory (personal communication, Steve Petersen). This same region found by Feiz and colleagues is thought to be involved with domain-general working memory.23
A possible interpretation is that UHL subjects need more subvocal rehearsal to stay on task than controls, so have strengthened this functional connection.
The conjunction analysis identified seed regions associated with auditory, sensorimotor, default mode, and phonological networks, as well as cingular opercular and frontoparietal task control networks, whose patterns of correlation differed between children with UHL and NH. Particularly noteworthy are the differences in the frontoparietal and cingulo-opercular networks, which are related to task level control, a type of executive function, involving rapid/adaptive and sustained/maintenance control, respectively.15, 24
Differences in brain networks responsible for these functions could explain some of the educational and behavioral problems experienced by children with UHL, and are further explicated below.
Regions from show correlations that are stronger in subjects with UHL than in controls. The middle temporal gyrus has been shown to be involved in auditory sentence comprehension in children.25
Atypical functional connectivity with the parahippocampal gyrus might handicap children with UHL since it has been widely implicated in both place processing and episodic memory, while Aminoff et al. argue that parahippocampal cortex plays a central role in contextual associative processing.26
The mid-cingulate region has been associated with cognitive processes such as error detection, salience, decision-making, attention to stimuli and anticipation.27
Sensorimotor seeds showed atypical connectivity with all of our conjunction analysis regions, including but not limited to motor mouth regions. This finding may help explain the high rates of speech problems and need for speech therapy among children with UHL in this study.
The implications of decreased functional connectivity in the medial globus pallidus (), an output nucleus of the basal ganglia, are unclear. Globus pallidus has been implicated in disorders of attention and impulsivity,28, 29
so perhaps future studies should quantify even subclinical attention and impulsivity issues in UHL patients and controls.
A recent fMRI study comparing children with UHL to children with NH using narrowband noise and speech-in-noise tasks found that children with UHL had less activation of auditory, auditory association, and attention areas than NH controls.30
Our study adds to Propst et al.'s results since the design differs in two primary ways. First, our study looked at functional connections in subjects at rest instead of using tasks to identify brain activations. Second, we identified possible differences in connections to executive function, default, and sensorimotor regions in addition to auditory pathways. Both studies found differences between NH controls and children with UHL that warrant further study.
A major limitation of our study is the small sample size. As this was a pilot study, our primary goal was to demonstrate that it is possible to identify differing patterns of inter-regional brain connectivity in children with UHL versus siblings with NH. Now that we have demonstrated the feasibility of our methods and generated preliminary data, we will expand the study to include more participants as well as examine differences in the language regions of the brain such as Broca's and Wernicke's areas, and those involved in visual processing.
In addition to performing rs-fcMRI scans on the subjects we have included thus far, we performed cognitive, achievement, language, and audiologic testing on each subject scanned, which we will correlate with the rs-fcMRI data. We will use these data to identify relationships between patterns of brain network activity and specific education-related difficulties in children with UHL. Understanding these networks could lead to targeted interventions, beyond amplification of sound to the impaired ear, and possibly better educational outcomes. Collectively, these findings could ultimately affect the provision of sensory devices and rehabilitation strategies specific to UHL.