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Brief description/objective

​Attention deficit (hyperactivity) disorder (AD(H)D) is one of the most common behavioral disorders in children and adolescents, with a worldwide prevalence of about 5% (Polanczyk et al., 2007; American Psychiatric Association, 2013). A substantial percentage of children remain affected into adulthood. While hyperactivity may decay over time, inattention and impulsivity often persist (American Psychiatric Association, 2013). For adults, a worldwide prevalence of 2.5% is reported (American Psychiatric Association, 2013). In recent decades, the diagnosis AD(H)D has become widely known and developed into a contentiously discussed issue of social relevance and great public interest.

AD(H)D is characterized by the key symptoms of hyperactivity, impulsivity, and/or inattention. Polygenetic influences seem to play a role in the development of AD(H)D (Gizer et al., 2009; Willcutt et al., 2012). Comorbid disorders, such as oppositional defiant disorder, conduct disorder, specific learning disorders, and disruptive mood dysregulation disorders, are frequent in patients with AD(H)D (American Psychiatric Association, 2013). With a ratio of about 2:1 in children and 1.6:1 in adults, males are more likely to be affected by AD(H)D than females (American Psychiatric Association, 2013). In contrast, compared with males, females more frequently display primarily inattentive features (American Psychiatric Association, 2013). Therapies consist mainly of stimulant medication, such as methylphenidate, and/or behavior modification therapy (M. T. A. Cooperative Group, 2004). To date, AD(H)D has been principally diagnosed on the basis of patterns of observable behavior, which can lead to diagnostic variability among informants, cultures, and countries (Polanczyk et al., 2007). Moreover, the interrater agreement of AD(H)D is low to moderate, a finding that is found across a lot of measures of psychopathology (Willcutt et al., 2012), pointing out the need of an objective diagnostic procedure.

To date, it is known that children of in mean about 11 years with ADHD, ADD and dyslexia show following neurological characteristics (Serrallach et al. 2016): In the left hemisphere, all three disorder subgroups show systematically smaller Heschl's Gyri (HG) and consequently enlarged Planum temporale (PT) volumes, resulting in considerably smaller left HG/PT ratios as compared to controls (Figure 1 B). A more specific pattern can be seen in the right hemisphere. Here, HG/PT ratios are generally higher and about the same in controls and ADD children, but significantly decreased in children with ADHD and dyslexia (Figure 1 B).

Moreover, the auditory evoked fields in response to the sounds of musical instruments and harmonic complex tones, as measured by MEG, show characteristic differences. When focusing on the first positive response complex (P1), peaking around 60–110 ms after tone onset all three disorder subgroups show an aberrant mean P1 source. Relative to normal controls, sources are located significantly more posteriorly in the left hemisphere in children with dyslexia, ADHD, and ADD. While controls show fairly symmetric P1 sources in left and right HG, all disorder subgroups are characterized by atypical locations on left PT. Controls show well-balanced bilateral responses with almost no or a slight absolute P1-asynchrony. In the disorder subgroups, such asynchronies are about five times larger. Moreover, the disorder subgroups are characterized by specific source waveform shapes. In dyslexics, the P1 peak is enlarged in the right-hemisphere, while in ADHD-children the response patterns are temporally expanded in the left and diminished in the right hemisphere. ADD children show similar, but time-shifted waveform shapes on both sides.

Furthermore, behavioral performance of basic sound processing (discrimination of frequency, intensity, onset ramp, and tone duration) and more complex auditory pattern recognition, such as meter, rhythm, melody, and pitch perception, differed significantly. As compared with the control group, dyslexics performed significantly poorer in almost all categories. Children with ADHD were characterized only by lower scores in melodic and rhythm processing, whereas children with ADD did not show any auditory impairment at all.

A combination of all relevant parameters lead to an excellent diagnostic accuracy of up to more than 90% concerning the capacity to correctly identify cases with dyslexia, ADHD, and ADD.

The social relevance of the topic AD(H)D can be seen in the fact, that this previous article investigating the neuro-auditory profile of children with AD(H)D (Serrallach et al., 2016) received extraordinary public attention, which is evident from the official Altmetric data base, comparing ~ 6.3 billions of scientific articles worldwide. Based on this huge data base and standardized criteria, it was assigned a percentile rank of 93, which means that only 7 percent of ever published studies have received higher public attention.

As mentioned above, in adults, hyperactivity may decay over time while inattention and impulsivity often persist (American Psychiatric Association, 2013). We are interested to see how this appears in the neuro-auditory profile of adults with ADHD and ADD. As a next step to the future perspective of developing a brain-based objective diagnostic procedure by using neuroanatomical and neurofunctional parameters of the auditory cortex, previously found result must be reproduced in more subjects and in a greater age range. Due to the fact, that dyslexia can be objectively diagnosed, in this study we want to concentrate on the disorders ADHD and ADD.

However, in order for these diagnostic procedures to become commonly accepted and used, different requirements and conditions must first be fulfilled. Both the MEG and MRI are non-invasive and non-hazardous methods. While MRI facilities are easily available and easily accessible, MEG facilities are only available in a limited number of specialized research institutions and are very cost-intensive. Hence, a more easily accessible and low-priced alternative to MEG would be needed. EEG could be an appropriate alternative. However, even though MEG has a couple of advantages over EEG such as the measurement of tangential components that optimally match the inward-folded anatomy of the human auditory cortex, and more accurate source modelling, both methods are well-suited to investigate different aspects of neural synchronization within and across hemispheres. Therefore, we plan a combined MEG-EEG measurement for reference.