Brain structural and functional organization in children with APD

Can brain imaging tell us about how the brain differs in children with APD compared to children without hearing complaints? Or could it show us where this anomaly happens in their brain? Researchers at the School of Psychology within the University of Auckland answer this question.

Auditory Processing Disorder (APD) is a condition where children have trouble understanding speech and other complex sounds, especially in noisy environments, despite (typically) having normal hearing for pure tones. APD affects how the brain processes auditory information, leading to challenges in listening, comprehension, and communication. APD often co-occurs with other developmental disorders like ADHD and dyslexia. It is estimated that 6.2% of school-aged children could have APD in New Zealand.1

There has been a long-standing debate whether this difficulty originates in the hearing system where auditory cues are being received or in brain regions, where higher order cognitive and language processing occurs. Since there have been few studies looking at the brain specifically, researchers at the University of Auckland conducted a large-scale neuroimaging study using a Magnetic Resonance Imaging (MRI) scanner to investigate this question.

Researchers hypothesized that both functional and structural differences in brain organization contribute to the difficulties experienced by children with APD. Our functional MRI study focused on brain activity patterns, while the structural MRI study examined the physical connections within the brain.

Research methods and approaches

Neuroimaging involves the use of various techniques to visualize the structure and function of the brain. In these studies, two types of neuroimaging were used.

More than 66 children participated in this research during the global pandemic – however, only 57 were retained for further analysis due to factors such as too much movement in the scanner. Children had a hearing assessment that included audiometry and the Listening in Spatialized Noise-Sentences Test (LISN-S), which evaluates sentence recognition in noise (competing speech), as well as two stages of MRI assessments.

  1. Functional MRI (fMRI):
    • Purpose: To capture brain activity during resting state.
    • Procedure: Participants were asked to stay awake and look at a cross on the screen (to avoid distraction) while lying in an MRI scanner. The fMRI measures brain activity by detecting changes in blood flow, highlighting which brain areas are active during the measurement period.

  2. Diffusion MRI (dMRI):
    • Purpose: To analyze the brain’s white matter and structural connections.
    • Procedure: This technique uses the movement of water molecules to map out the pathways of white matter fibers in the brain. By examining these pathways, researchers can see how different brain regions are connected and identify any structural differences between children with APD and healthy controls. To keep the children entertained, they watched a video while this recording happened. A Lego model of an MRI machine (Figure 1) was used to help children understand what to expect during the scan.
Figure 1: Lego model of MRI machine

Understanding brain mechanisms through network theory

Network theory, also known as graph theory, studies complex systems by examining connections between different parts. In such studies, the brain is modeled as a network consisting of nodes (brain regions), connected by signals that can be measured using fMRI or dMRI scans. This approach helps researchers understand how information flows through the brain and identify key areas that might be disrupted in disorders like APD.

An example of this approach

Think of the brain as a city. In this city, nodes represent key locations such as schools and hospitals, while edges – the connections between brain regions – are like roads linking these places. In a well-functioning city, roads efficiently connect all the important places. However, if some roads are damaged or missing, it can cause traffic jams or difficulties in traveling from one place to another.

Similarly, in the brain of a child with APD, disruptions in the connections (edges) between important brain regions (nodes) can lead to difficulties in sound processing. Therefore, looking at interconnected areas (hubs) and the connections between these interconnected hubs (Rich-club structure) could potentially answer our questions (the Rich-club structure is the main basis for information flow in any system).

Key findings

  • Children with APD showed different brain activity patterns compared to controls, particularly in regions involved in auditory processing and attention.

  • These variations suggest that children with APD process sounds differently, which contributes to their listening difficulties.

  • The dMRI study found that children with APD had altered neural connections in brain regions responsible for processing sounds, consistent with findings from the fMRI study.

  • Changes were seen in the brain’s “rich-club” organization, which consists of highly connected hubs that facilitate communication across different brain areas.

Clinical implications

  • Findings indicate that children with APD exhibit differences in both brain functional and structural organizations.
  • By understanding these differences, researchers can help develop more effective diagnostic tools and treatments to enhance listening and communication skills in affected children.

To learn more about this research, I invite you to read our recent publications in Neuroimage Clinical and Cerebral Cortex.


References

1. Keith, W. J., Purdy, S. C., Baily, M. R., & Kay, F. M. (2019). New Zealand Guidelines on Auditory Processing Disorder. New Zealand Audiological Society. Retrieved from https://audiology.org.nz/assets/Uploads/APD/NZ-APD-GUIDELINES-2019.pdf, accessed July, 2024.

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