Altered electroencephalographic networks in developmental dyslexia after remedial training: a prospective case-control study.

Electroencephalographic studies using graph theoretic analysis have found aberrations in functional connectivity in children with developmental dyslexia. However, how the training with visual tasks can change the functional connectivity of the semantic network in developmental dyslexia is still unclear. We looked for differences in local and global topological properties of functional networks between 21 healthy controls and 22 dyslexic children (8-9 years old) before and after training with visual tasks in this prospective case-control study. The minimum spanning tree method was used to construct the subjects' brain networks in multiple electroencephalographic frequency ranges during a visual word/pseudoword discrimination task. We found group differences in the theta, alpha, beta and gamma bands for four graph measures suggesting a more integrated network topology in dyslexics before the training compared to controls. After training, the network topology of dyslexic children had become more segregated and similar to that of the controls. In the θ, α and ß1-frequency bands, compared to the controls, the pre-training dyslexics exhibited a reduced degree and betweenness centrality of the left anterior temporal and parietal regions. The simultaneous appearance in the left hemisphere of hubs in temporal and parietal (α, ß1), temporal and superior frontal cortex (θ, α), parietal and occipitotemporal cortices (ß1), identified in the networks of normally developing children was not present in the brain networks of dyslexics. After training, the hub distribution for dyslexics in the theta and beta1 bands had become similar to that of the controls. In summary, our findings point to a less efficient network configuration in dyslexics compared to a more optimal global organization in the controls. This is the first study to investigate the topological organization of functional brain networks of Bulgarian dyslexic children. Approval for the study was obtained from the Ethics Committee of the Institute of Neurobiology and the Institute for Population and Human Studies, Bulgarian Academy of Sciences (approval No. 02-41/12.07.2019) on March 28, 2017, and the State Logopedic Center and the Ministry of Education and Science (approval No. 09-69/14.03.2017) on July 12, 2019.

Small-world EEG network analysis of functional connectivity in developmental dyslexia after visual training intervention.

Aberrations in functional connectivity in children with developmental dyslexia have been found in electroencephalographic studies using graph analysis. How training with visual tasks can modify the functional semantic network in developmental dyslexia remains unclear. We investigate local and global topological properties of functional networks in multiple EEG frequency ranges based on a small-world propensity method in controls, pre- and post-training dyslexic children during visual word/pseudoword processing. Results indicated that the EEG network topology in dyslexics before the training was more integrated than controls, and after training - more segregated and similar to that of the controls in the theta (θ: 4-8), alpha (α: 8-13), beta (ß1: 13-20; ß2: 20-30), and gamma (γ1: 30-48; γ2: 52-70 Hz) bands for three graph measures. The pre-training dyslexics exhibited a reduced strength and betweenness centrality of the left anterior temporal and parietal regions in the θ, α, ß1 and γ1-frequency bands, compared to the controls. The simultaneous appearance of hubs in the left hemisphere (or both hemispheres) at temporal and parietal (α-word/γ-pseudoword discrimination), temporal and middle frontal cortex (θ, α-word), parietal and middle frontal cortex (ß1-word), parietal and occipitotemporal cortices (θ-pseudoword), identified in the EEG-based functional networks of normally developing children were not present in the networks of dyslexics. The hub distribution for dyslexics in the θ, α, and ß1 bands became similar to that of the controls. The topological organization of functional networks and the less efficient network configuration (long characteristic path length) in dyslexics compared to the more optimal global organization in the controls was studied for the first time after remediation training.

Speech-Brain Frequency Entrainment of Dyslexia with and without Phonological Deficits.

Developmental dyslexia is a cognitive disorder characterized by difficulties in linguistic processing. Our purpose is to distinguish subtypes of developmental dyslexia by the level of speech-EEG frequency entrainment (δ: 1-4; ß: 12.5-22.5; γ1: 25-35; and γ2: 35-80 Hz) in word/pseudoword auditory discrimination. Depending on the type of disabilities, dyslexics can divide into two subtypes-with less pronounced phonological deficits (NoPhoDys-visual dyslexia) and with more pronounced ones (PhoDys-phonological dyslexia). For correctly recognized stimuli, the δ-entrainment is significantly worse in dyslexic children compared to controls at a level of speech prosody and syllabic analysis. Controls and NoPhoDys show a stronger δ-entrainment in the left-hemispheric auditory cortex (AC), anterior temporal lobe (ATL), frontal, and motor cortices than PhoDys. Dyslexic subgroups concerning normolexics have a deficit of δ-entrainment in the left ATL, inferior frontal gyrus (IFG), and the right AC. PhoDys has higher δ-entrainment in the posterior part of adjacent STS regions than NoPhoDys. Insufficient low-frequency ß changes over the IFG, the inferior parietal lobe of PhoDys compared to NoPhoDys correspond to their worse phonological short-term memory. Left-dominant 30 Hz-entrainment for normolexics to phonemic frequencies characterizes the right AC, adjacent regions to superior temporal sulcus of dyslexics. The pronounced 40 Hz-entrainment in PhoDys than the other groups suggest a hearing "reassembly" and a poor phonological working memory. Shifting up to higher-frequency γ-entrainment in the AC of NoPhoDys can lead to verbal memory deficits. Different patterns of cortical reorganization based on the left or right hemisphere lead to differential dyslexic profiles.

Functional correlates of brain aging: beta and gamma frequency band responses to age-related cortical changes.

The brain as a system with gradually declined resources by age maximizes its performance by neural network reorganization for greater efficiency of neuronal oscillations in a given frequency band. Whether event-related high-frequency band responses are related to plasticity in neural recruitment contributed to the stability of sensory/cognitive mechanisms accompanying aging or are underlined pathological changes seen in aging brain remains unknown. Aged effect on brain electrical activity was studied in auditory discrimination task (low-frequency and high-frequency tone) at particular cortical locations in beta (ß1: 12.5-20; ß2: 20.5-30 Hz) and gamma frequency bands (γ1: 30.5-49; γ2: 52-69 Hz) during sensory (post-stimulus interval 0-250 ms) and cognitive processing (250-600 ms). Beta1 activity less affected by age during sensory processing. Reduced beta1 activity was more widespread during cognitive processing. This difference increased in fronto-parietal direction more expressed after high-frequency tone stimulation. Beta2 and gamma activity were more pronounced with progressive age during sensory processing. Reducing regional-process specificity with progressing age characterized age-related and tone-dependent beta2 changes during sensory, but not during cognitive processing. Beta2 and gamma activity diminished with age on cognitive processes, except the higher frontal tone-dependent gamma activity during cognitive processing. With increasing age, larger gamma2 activity was more expressed over the frontal brain areas to high tone discrimination and hand reaction choice. These gamma2 differences were shifted from posterior to anterior brain regions with advancing age. The aged influence was higher on cognitive processes than on perceptual ones.

The effect of aging on EEG brain oscillations related to sensory and sensorimotor functions.

PURPOSE: The question of the present study is whether the brain as a system with gradually decreasing resources maximizes its performance by reorganizing neural networks for greater efficiency. MATERIAL/METHODS: Auditory event-related low frequency oscillations (delta δ - [2, 4]Hz; theta θ - [4.5, 7]Hz; alpha α - [7.5, 12]Hz) were examined during an auditory discrimination motor task (low-frequency tone - right hand movement, high-frequency tone - left hand movement) between two groups with mean age 26.3 and 55 years. RESULTS: The amplitudes of the phase-locked δ, θ and α activity were more pronounced with a progressive increase in age during the sensory processing, independent of tone type. The difference between the groups with respect to scalp distribution was tone-independent for delta/theta oscillations, but not for the alpha activity. Age-related and tone-dependent changes in α band activity were focused at frontal and sensorimotor areas. Neither functional brain specificity was observed for the amplitudes of the low-frequency (δ, θ, α) oscillations during the cognitive processing, which diminished with increasing age. CONCLUSION: The cognitive brain oscillatory specificity diminished with increasing age.

Auditory event-related brain potentials for an early discrimination between normal and pathological brain aging.

The brain as a system with gradually decreasing resources maximizes its chances by reorganizing neural networks to ensure efficient performance. Auditory event-related potentials were recorded in 28 healthy volunteers comprising 14 young and 14 elderly subjects in auditory discrimination motor task (low frequency tone - right hand movement and high frequency tone - left hand movement). The amplitudes of the sensory event-related potential components (N1, P2) were more pronounced with increasing age for either tone and this effect for P2 amplitude was more pronounced in the frontal region. The latency relationship of N1 between the groups was tone-dependent, while that of P2 was tone-independent with a prominent delay in the elderly group over all brain regions. The amplitudes of the cognitive components (N2, P3) diminished with increasing age and the hemispheric asymmetry of N2 (but not for P3) reduced with increasing age. Prolonged N2 latency with increasing age was widespread for either tone while between-group difference in P3 latency was tone-dependent. High frequency tone stimulation and movement requirements lead to P3 delay in the elderly group. The amplitude difference of the sensory components between the age groups could be due to a general greater alertness, less expressed habituation, or decline in the ability to retreat attentional resources from the stimuli in the elderly group. With aging, a neural circuit reorganization of the brain activity affects the cognitive processes. The approach used in this study is useful for an early discrimination between normal and pathological brain aging for early treatment of cognitive alterations and dementia.

Beta and gamma frequency-range abnormalities in parkinsonian patients under cognitive sensorimotor task.

Parkinson's disease (PD) is a neurodegenerative disorder caused by a disruption of dopaminergic neurotransmission in the basal ganglia. Some of PD clinical symptoms are suggested to stem directly from the excessive synchrony between the basal ganglia and cortical circuits. Our present investigation explores the functional relationships between event-related desynchronization/synchronization (ERD/ERS) of beta and gamma band activity for idiopathic non-demented Parkinson's patients (PP) and control subjects (CS) during auditory discrimination tasks between two tone types (LT: 800 Hz, HT: 1000 Hz) within two post-stimulus intervals of 0-250 and 250-600 ms. Beta1 (13-20 Hz) ERD was found for both groups within both intervals more expressed in CS except for frontal beta1 synchronization in CS during the second interval. Beta2 (20-32 Hz) ERD was revealed in CS after both tones during both post-stimulus intervals. Beta2 ERS was only observed in PP. The most prominent beta2 ERS followed HT during the second interval. Gamma frequency (32-50 Hz) ERD was found in both groups except for fronto-parietal ERS for PP during the first interval after LT. During the second interval, either tone, we found prominent ERS for PP and ERD for CS everywhere except for a frontal ERS after HT. Deviations of the beta and gamma ERD/ERS for the PP compared with CS during the sensorimotor and cognitive processing are a clear evidence for disturbances in the temporal and regional integration of these frequency components and the relationships between cortical and the basal ganglia circuits in parkinsonism.

Neurons in primary motor cortex engaged during action observation.

Neurons in higher cortical areas appear to become active during action observation, either by mirroring observed actions (termed mirror neurons) or by eliciting mental rehearsal of observed motor acts. We report the existence of neurons in the primary motor cortex (M1), an area that is generally considered to initiate and guide movement performance, responding to viewed actions. Multielectrode recordings in monkeys performing or observing a well-learned step-tracking task showed that approximately half of the M1 neurons that were active when monkeys performed the task were also active when they observed the action being performed by a human. These 'view' neurons were spatially intermingled with 'do' neurons, which are active only during movement performance. Simultaneously recorded 'view' neurons comprised two groups: approximately 38% retained the same preferred direction (PD) and timing during performance and viewing, and the remainder (62%) changed their PDs and time lag during viewing as compared with performance. Nevertheless, population activity during viewing was sufficient to predict the direction and trajectory of viewed movements as action unfolded, although less accurately than during performance. 'View' neurons became less active and contained poorer representations of action when only subcomponents of the task were being viewed. M1 'view' neurons thus appear to reflect aspects of a learned movement when observed in others, and form part of a broadly engaged set of cortical areas routinely responding to learned behaviors. These findings suggest that viewing a learned action elicits replay of aspects of M1 activity needed to perform the observed action, and could additionally reflect processing related to understanding, learning or mentally rehearsing action.

Event-related desynchronization/synchronization during discrimination task conditions in patients with Parkinson's disease.

Parkinson's disease is a neurodegenerative disorder with symptoms, which include movement disturbances and changes of cognitive information processing. The aim of the present study was to investigate the functional relationships between oscillatory electroencephalographic (EEG) dominant components with event-related desynchronization/synchronization (ERD/ERS) method for idiopathic non-demented Parkinson's patients (PP) and control subjects (CS) during auditory discrimination tasks within two post-stimulus intervals of 0-250 and 250-600 ms. When comparing the CS and PP during the first post-stimulus period, we found delta- and theta-ERS significantly pronounced in CS for both tone types (low--800, high--1,000 Hz) with the following exceptions: at Fz, PP displayed higher delta-ERS, while at C3' theta-ERD in response to a high tone. Alpha-ERS was found in PP in response to either tone at all electrodes and mainly alpha-ERD in CS. In the second post-stimulus interval, the significant differences between the groups were: (i) delta-ERS in CS and delta-ERD in PP in response to the low tone and (ii) delta-ERS for both groups in answer to the high tone, more prominent in CS at Cz and Pz, except for delta-ERD in PP at C3'. For both groups, we detected predominantly theta-ERD and alpha-ERD following both tone types within this second interval. PP showed more expressed theta-ERD at Fz and parietal theta-ERS. Alpha-ERD was significantly higher in CS, while frontal alpha-ERD was more prominent in the PP in response to both tones. The data obtained showed specific functional differences of event-related oscillatory activity in cognitive and sensory-motor information processing between the PP and CS.

Method for ventricular fibrillation detection in the external electrocardiogram using nonlinear prediction.

The automatic external defibrillator is a lifesaving device which processes and analyses the electrocardiogram (ECG) and delivers defibrillation shock when necessary. The accuracy of the built-in algorithm for ECG analysis must be very high, with sensitivity and specificity aimed to approach the maximum values of 100%. An algorithm based on nonlinear prediction of the external ECG signal is proposed. It extracts seven parameters characterizing the prediction possibility of the assessed ECG signal. By means of the K-nearest neighbours rule the diagnostic accuracy of different combinations of these parameters was evaluated. Thus the accuracy obtained was higher than 95% with sensitivity and specificity values depending on the combination of parameters. The method was tested with ECG records from the widely recognized databases of the American Heart Association (AHA) and Massachusetts Institute of Technology (MIT).