Psychophysiological Characteristics of Children with Dyslexia

Dyslexia is a specific learning disorder that involves difficulty reading due to decoding problems for letters and words. Statistics shows that 5-10% of the general population has dyslexia. The aetiology of reading disorder supposes some biological causes and morphological markers useful in the classification and early identification of the problem. The aim of this article is to find appropriate parameters, which will be useful for early diagnosis and finding the right modalities for treatment. Our findings about QEEG characteristics are not conclusive. However, slowing of brain activity in dyslexic children appeared to be confirmed. These findings lead to the possible hypothesis of delay in neurological development of these children. Significant theta/beta ratio suggest possible comorbidity with ADHD. Further research with more children included is proposed.

Unfortunately, in our country the special test for dyslexia does not exists. The most used test is Macedonian translation of test developed by Kostic, Vladisavljevic and Popovic (1983) (Kostic, Vladisavljevic, Popovic, & Cudov, 1983). Some experiences in the assessment of children with dyslexia, dysgraphia and dyscalculia in our context, were published by a group of researchers from the Institute for Special Education, UKIM, Skopje in 2018 (Karovska-Ristovska, Kardaleska, Ajdinski, & Shurbanovska, 2018).
For this reason, and the scarce of data for dyslexia in our country, the aim of this research is to find appropriate parameters, which will be useful for early diagnosis and finding the right modalities for treatment. Such parameters would be possible specific abnormalities in EEG recordings, as well as the performances of these children tested with own modality we named as "Neurogame" which helps to evaluate concentration, focus attention and reaction time to some tasks. As far as we know, this is the first study that evaluates this issue in our country.

Sample
We selected randomly 10 children diagnosed as dyslexic according to ICD-10 and DSM-V criteria, referred by the Institute for child mental health in Skopje. The diagnostic was made from the team consisted of logopaedist, psychologist, child neurologist, paediatrician as well as child psychiatrist.
Mean age of boys was 10.2±1.64 years and mean age of girls was 9.2±1.60 years. The written consent was obtained from parents. In the moment of evaluation children were in good health and without any medication 48 hours before recording.

Evaluation
EEG was recorded using a Mitsar 201 (www.mitsar-medical.com), a PC-controlled 19-channel electroencephalographic system with 19 electrodes, placed according to the international 10-20 system, referenced to linked ears (on the International 10-20 system) with 250 Hz sampling rate in 0.5-50 Hz frequency range in the following conditions: Eyes opened (EO)-5 minutes, and Eyes closed (EC)-5 minutes as well as stimuli presentation protocol (Visual Continuous Performance test-VCPT). The obtained data from VCPT, are not aimed for analysis in this paper and this data will be analysed in another paper.
The same equipment and procedures were used for children with dyslexia and controls. Subjects were tested in a quiet air-conditioned room with the experimenter and recording equipment present. During fitting of the electrodes, subjects were familiarized with the testing equipment and the procedure.
Vertical Electro-Oculogram (VEOG) was recorded with 2 tin electrodes placed 1 cm above and 1 cm below the right eye. Eye-blink artifacts were corrected by zeroing the activation curves of individual ICA component score responding to eye blinks. In addition, epochs of the filtered electroencephalogram with excessive amplitude (>100 μV) and/or excessively fast (>35 μV in 20-35 Published by SCHOLINK INC. excluded from further analysis. Finally, EEG was manually inspected to verify artifact removal. Spectral analysis of relative power using fast Fourier transform was carried out for the four frequency bands: delta (0.5-4 Hz), theta (4-8 Hz), alpha (8-12 Hz), and beta (12-20 Hz). Relative power is represented by the percentage of the amplitude in a given frequency band compared with the total amplitude across all frequency bands. Also, we calculated the ratio between theta and beta absolute power in order to obtain the theta-beta ratio (TBR) at Cz.
In some article it was published that asymmetric feature for QEEG recording was typical for dyslexic children. Asymmetry is defined as a functional difference between the left and right hemispheres measured for relative power which exists between the homologous electrodes located on both hemispheres. It was calculated using the following equation:

Power (Left) -Power (Right) / Power (Left) + Power (Right)
where Power (Left) corresponds to the relative power of the electrode located on the left hemisphere, and Power (Right) to the relative power on the right hemisphere. These asymmetry data were statistically analysed.
Before the QEEG recording, "Neurogame" was applied. Our original developed application on Android operating system, named "Neurogame" is based on an open source platform to enable assessment the focus and concentration, as well as reaction time, with the ability to monitor the progress of the results over a period of time. The testing for all clients was performed in the morning period 8-12 am (Hughes, 1978). The complete evaluation of children takes around 2 hours.

Data Analysis
The Statistica StatSoft software was used to assess group differences. One-way analysis of variance Additionally, we include and electrodes above Broca's area (F3, F7 and C3) and Wernicke's area (T3, T5 and P3). Group (dyslexia and control) was the between-subject factor. For some estimations because of the small sample size, the non-parametric Mann-Whitney U test was used to lower variability in the groups. The level of significance was set at p < .05.

Results
As mentioned before, the evaluated sample is small, consisting of 10 children, where mean age of boys was 10.2±1.64 years and mean age of girls was 9.2±1.60 years. The results are compared with matched control group consisting of 10 children with normo-typical development without any learning problems or neurodevelopmental delay. Mean age of boys in the control group was 10.4±1.84 years and mean

Frontal, Central, Temporal, Parietal and Occipital Positions
For alpha (frontal, central and temporal) and beta we obtained almost the same results for both groups without any significance ( Figure 2).     Calculated Student t-test for parameters between groups is presented on Figure 11. It is clear that only time for maximum hits is statistically significant; all other parameters are similar for both groups.

Figure 11. T-test for Independent Samples (Dyslexia vs Healthy)
Generally, results obtained with "Neurogame" are similar for dyslexic children and matched control healthy school children.

Discussion
A wide range of research has investigated what people understand about dyslexia. In this context, electrophysiological measures of brain function are used as effective tools to understand neurocognitive phenomena and as sensitive indicators of pathophysiological processes of this disorder.
The aim of the present study was to examine group differences in spontaneous oscillatory brain activity during a resting (eyes opened) condition. EEG power was examined across all frequency bands in children with dyslexia and contrasted to neurotypical children.
As presented, our group of dyslexic children did not differ significantly for results obtained by QEEG. It is obvious that the only difference is general slowing in brain activity and significantly higher theta/beta ratio found in dyslexic group.
wave activity (for both delta and theta), in Broca's compared to Wernicke's area, which was in direct contrast to the control children who did not exhibit any asymmetry across these two areas. Children with dyslexia also had significantly decreased EEG power on the left for alpha2 and beta frequency bands, but had significantly increased EEG power in the left hemisphere for the theta band.
Our analysis for asymmetry of relative power did not confirmed any hemispheric asymmetry in dyslexic children.
Oscillatory dynamics of brain activity during processing of words and non-words was analysed thought analysis of EEG signals. Starting from the knowledge that reading is a complex cognitive skill sub served by a distributed network of visual and language-related regions, Žarić G. et al. (Žarić, 2017) investigated whether directed connectivity during reading scales with the level of dysfluency in dyslexic children exist. Obtained results of this study suggest disrupted visual processing of words in both dyslexic groups, together with a compensatory recruitment of right posterior brain regions. Functional connectivity in the brain's reading network may thus depend on the level of reading dysfluency beyond group differences between dyslexic and typical readers.
The finding that the functional connectivity pattern in dyslexic children is related to their reading level, may in part explain the mixed results obtained in previous functional connectivity studies of dyslexia.