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T Harmony

Publications and source records attributed to T Harmony.

17 recordsLinked to original sources
PubMed1992

Maturation of the coherence of EEG activity in normal and learning-disabled children.

The age effect on coherence has been studied in control (98) and learning-disabled (LD, 54) school-aged children (from 6.0 to 16.8 years old). The EEG recordings were made at rest in 15 leads, and 105 pairwise combinations for coherence were calculated (each lead was compared with all the rest) for delta, theta, alpha, beta and total frequency bands. A significant increase of coherence with age was found in both groups, with a different pattern of maturation. In the control group, a significant increase with age was found in the coherences between posterior regions and vertex (Cz). A significant decrease with age in the coherence between frontal areas was observed, especially in the theta band. The LD group showed a different pattern: no significant relation with age was found in the coherence between any lead and vertex. A high effect of age on coherence between temporal regions was observed with a predominance of the left side in comparison with the contralateral and the ipsilateral. No decrease in frontal coherence was found: in the same region where the control group showed negative values with age, the LD groups had no age effect. The results obtained are discussed as differences in brain organization, in myelogenesis and synaptogenesis and an explanation of the etiology of LD is proposed.

Adolescent↗
PubMed1992

Visual evoked potentials, attention and mnemonic abilities in children.

We analyzed the correlation between attention and mnemonic processes and different visual evoked potential (VEP) parameters. A group of 34 children between 9 and 13 years old was studied. VEPs were recorded in C3, C4, P3, P4, O1, O2, T5 and T6 with linked ear lobes as reference. Two different types of stimuli were used: flash and checkerboard pattern. The power of VEPs was calculated as the sum of the square amplitude values for different time epochs. Correlation coefficients between left and right homologous VEPs were also computed. A visual selective attention task divided into 5 items of increasing difficulty and the Sternberg paradigm were applied. The performance was automatically evaluated by the computer, giving the number of correct responses (NCR) and other measures of performance. Correlation coefficients between VEP parameters and the scores obtained in the performance of tasks were calculated. It was observed that power in P3, P4, T5, and T6 and the correlation coefficients between central, parietal and temporal VEPs were positively correlated with NCR of both tasks. However, power in O1 and O2 was negatively correlated with NCR.

Adolescent↗
PubMed1991

Event related potentials recorded in normal and dyslexic subjects when reading in and out of context.

Clinical evidence has shown that expectancy or anticipatory reactions influence the ability to read. It is possible that the reading problems shown by dyslexic children could be due to the absence of anticipatory hypotheses when they decode verbal material. Research was therefore carried out into these clinical observations to see if they could be detected on an electrophysiological level using a technique for recording Event Related Potentials (ERPs). In this study, our intention was to observe if there were any differences between a sample population of normal children and one of dyslexic children in the ERPs recorded on the presentation of words both in and out of context. The words recorded during the reading in context were: the word "la" (the feminine article "the" in Spanish), an "intermediate" word and a "final" word in a series of sentences. The first two have a greater anticipatory load than the reading of the final word since this is the word that closes the meaning of the sentence. Furthermore, as a control, the ERPs that were produced when reading isolated words were recorded, a situation that does not require the presence of anticipatory processes. The control group was made up of subjects with adequate school performance and no pathological background, and the experimental group was composed of subjects whose performance on a psychoeducational battery, previously administered to 120 Mexican children, had been found to be two standard deviations below the established norms. Following the 10-20 international system, electrodes were placed in zones F3, Cz, P3, O1 and O2 and referred to both earlobes. Statistical analysis revealed significant differences between groups in the amplitude of the ERP recording in the left occipital zone for all conditions when reading in sentences ("la," "intermediate" and "final"). It is suggested that this cortical zone participates in decoding verbal material and that it is deficient in subjects with reading problems.

Adolescent↗
PubMed1991

EEG and skeletal development in children with different psychosocial characteristics.

Two groups of children with different socioeconomic level were studied. One minute EEG at rest was recorded in monopolar leads F3, F4, C3, C4, P3, P4, O1, O2, F7, F8, T3, T4, T5 and T6. Absolute and relative power in four EEg bands (delta, theta, alpha and beta) were computed. Radiographies of the left hand and the wrist were also obtained in all children. Age regression equations of the variables derived from EEG spectra were calculated in each group. In the group with low socioeconomic level many children had antecedents of risk factors. In this group absolute and relative power in the four bands presented a great dispersion and no correlation with age. In the group with good socioeconomic level the age regression equations of the EEG variables were significant, absolute values in the four bands decreased with age, as well as delta and theta relative power, while alpha and beta relative power increased with age. The area of the ossification center of each bone of the hand of the lower end of the ulna and radius were obtained from the X-ray film. Linear regression equations for the area of each ossification center were significant in both groups. No intercept or slope differences existed between both groups in any area. It is concluded that psychosocial disadvantage and antecedents of risk factors, although not producing any effect on skeletal development, do affect EEG maturation.

Adolescent↗
PubMed1990

Effect of sex, psychosocial disadvantages and biological risk factors on EEG maturation.

Broad-band frequency analysis was performed on the EEGs of school-age children in order to study the effects of sex, socioeconomic status (SES) and biological risk factors on EEG maturation. Absolute power and relative power in delta, theta, alpha and beta frequency bands were computed in monopolar recordings from F3, F4, C3, C4, P3, P4, O1, O2, F7, F8, T3, T4, T5 and T6. Total absolute power and power in the delta and theta bands decreased with age, following a quadratic polynomial expression. Relative power followed a linear regression with age. Delta and theta decreased while alpha and beta increased. Sex differences in relative power were observed, possibly related to a pubertal spurt: slopes of regression equations were steeper in girls than in boys. Children from low SES (very low income and/or illiterate mother) had higher values of absolute power and a higher percentage of delta and lower of alpha than children with good SES, suggesting a maturational lag. A group of children with personal antecedents of risk factors associated with brain damage were compared with children without antecedents. The former group had higher values of absolute power. Depending on the severity of the risk, children with more severe antecedents had greater differences from children with no antecedents than children in whom antecedents were considered as slight. Risk antecedents had no effect on relative power.

Age Factors↗
PubMed1990

Correlation between EEG spectral parameters and an educational evaluation.

EEG spectral parameters were computed in a group of children with different degrees of difficulty in learning to read and write. For statistical analyses, Z-transformed values according to normative age-regression equations were used to control the age effects. Canonical Correlation Analysis between absolute power in different bands and the categories of the educational evaluation (good, regular, poor and very poor) showed that more delta was probably related to a poor evaluation and more alpha in occipital areas to a good one. MONOVA also showed highly significant differences in the absolute power in many leads between children with different evaluations. As children with a poor evaluation very frequently had antecedents of risk factors related to brain damage and were from a low socioeconomic status, and both factors have been shown to affect absolute power, it may be that the differences observed were due to these causes. However, relative power correlated more with the learning problems. Children with minor difficulties, with no antecedents and with good socioeconomic status had more theta in almost all leads than children with a good evaluation and with the same characteristics. Children with a poor, or very poor, evaluation had more delta in left frontal and temporal areas (F3, F7 and T3) which may reflect underlying cerebral dysfunction of these regions directly involved in reading and writing processes.

Child↗
PubMed1990

The late event related potentials CNV and PINV in normal and dyslexic subjects.

The most prominent ERP to occur during intervals of preparation and anticipation is the contingent negative variation (CNV) or expectancy wave. The resolution of this wave is called the postimperative negative variation (PINV). The purpose of this study was to distinguish the characteristics of the CNV and the PINV in a group of children with reading disabilities or dyslexia and to compare them from a group of normal readers. Nine righthanded boys aged between 10-13 years with reading disabilities were studied. The children were matched with a group of nine normal readers. Four derivations were used: frontal, central, parietal and occipital zones, with reference to linked ears. Data were analyzed using multivariate procedures. Significant differences between groups in CNV amplitude and in PINV amplitude and latency at the left parietal site were observed. We discuss the participation of this zone and we consider processes like expectancy, attention and brain activity signal processing in the differences mentioned.

Adolescent↗
PubMed1990

Brainstem evoked potentials in learning disabled children.

Averaged brainstem auditory responses (BAER) were recorded using left and right ear stimulation with clicks of 90 dBs in two groups of primary school children (control and learning disabled). A linear multiple regression model was used in an attempt to demonstrate the effects of sex, high risk factors related to brain damage and learning disability on the evoked responses. Sex showed a strong influence in the latencies of the first five peaks, with girls having shorter latencies. Risk factors had an effect on the latency of peak V, the I-V interval and the V/I amplitude ration, but only when the left ear was stimulated. Learning disability had no significant influence according to this analysis. Multivariate test of complete homogeneity showed highly significant differences between LD and control boys when the left ear was stimulated and between control and LD girls when the right ear was stimulated. Principal component analyses revealed differences between the two groups: the BAER components of the control subjects showed a minor source of variance when the right ear was stimulated. A contrary effect was observed in LD children. Such differences might be related to ear preference and hemispheric dominance.

Acoustic Stimulation↗
PubMed1978

Visual, auditory and somatosensory evoked responses in patients with cerebrovascular disorders.

A diagnostic evoked response battery, consisting of visual evoked responses to flashes and to a checkerboard pattern, auditory evoked responses to three different tones and somatosensory evoked responses to left, right and bilateral median nerve stimulation, was administered to 20 patients with strokes, and compared with 20 normal control subjects. Recordings were obtained at C3, C4, O1, O2, T3 and T4. Evoked responses were found to be of lower amplitudes and lower amplitudes and lower waveform symmetry (expressed by low correlation coefficients between left and right homologous areas) in the patients than in normal subjects. A discriminant equation with 17 variates was computed to separate the two groups. One patient (5%) and 2 (10%) normal subjects were misclassified. Comparison between patients with left or right lesions showed that somatosensory and auditory evoked responses were very useful for identification of the affected side. Quantitative study of evoked responses to different types of stimuli and sensory modalities provides a sensitive method for the evaluation of brain function in such patients. This technique gives higher accuracy than the routine EEG examination in terms of both the percentage of dectection and the accuracy of localization of the affected side.

Acoustic Stimulation↗
PubMed1977

Neurometrics.

Explore the source record for details and available documents.

Aged↗
PubMed1975

Driving activity. A quantitative study.

A comparative study of driving activity between normal subjects and neurological patients was performed. Driving activity was considered as the energy of the visual evoked potentials filtered at the same frequency of stimulation (1, 2, 4, 7, 10, 12 and 15 cps) using a CAT 400 C computer as a digital filter. The hemispheric symmetry of the responses was measured by the Pearson product moment correlation coefficient and the signal energy ratio. Each symmetry measure for every patient was compared with the normal values and considered abnormal when differences were greater than 3 SD from the normal mean. Of 25 patients 14 of them with a normal EEG, 23 presented severe alterations in the symmetry of the filtered visual evoked responses. Each patient showed a peculiar pattern of abnormality. It is concluded that the procedure described is a very powerful method in the discrimination of brain lesions.

Adolescent↗
PubMed1975

Polarity coincidence correlation coefficient and signal energy ratio of the ongoing EEG activity. II. Brain tumors.

The asymmetry of the EEG in 35 patients with brain tumor was analyzed using a special purpose computer which provided two measures: Polarity Coincidence Correlation Coefficient (PCC) and Signal Energy Ration (SER). Significant differences were found between this group and a control group of normal subjects. A discriminant function was calculated using both measures and gave an overall separation accuracy of 87% in the sample studied. It was concluded that the method described offers great utility in routine screening and diagnosis of brain tumors.

Adolescent↗
PubMed1975

Polarity coincidence correlation coefficient and signal energy ratio of the ongoing EEG activity. III. Cerebral vascular lesions.

The EEG symmetry of 65 patients with different kinds of cerebrovascular disorders was analyzed using the Polarity Coincidence Correlation Coefficient (PCC) and the Signal Energy Ratio (SER) measurements. Significant differences were found between the pathology group and a control group of normal subjects for both measures. A discriminant function was applied for both values with an overall accuracy of 80%. It is concluded that since the method does not require an experienced electroencephalographer it may be useful for the diagnosis of cerebrovascular pathology and for screening purposes.

Adolescent↗
PubMedDate not supplied

Computer tomography in children with electrophysiological abnormalities.

A computed tomography examination was carried out in a group of 43 children, of whom 15 had learning disabilities (LD). Children were selected with electrophysiological abnormalities in the routine EEG, in the quantitative EEG analysis and/or in the visual cortical and auditory brainstem evoked responses. Seven children, 1 control and 6 LD, had abnormalities in the computed tomography. The most frequent localization of the lesion was the left temporal lobe. This localization might explain the origin of the learning disorder, since the left temporal lobe is involved in reading and writing processes. There was a great concordance between the anatomical localization of the lesion by the computed tomography and the place of electrical abnormalities in the quantitative EEG and the visual evoked responses. These results strongly support the indication of a computed tomography examination in LD children.

Adolescent↗
PubMedDate not supplied

[Visual somatosensory and auditory evoked potentials in multiple sclerosis].

In a group of 15 patients with multiple sclerosis and in a control group of 20 healthy subjects visual evoked potentials produced with flashes or checkerboard pattern, auditory evoked potentials after stimulation with three different tones, and somatosensory evoked potentials after stimulation of the left, right or both median nerves, and reactions to stroboscopic stimulation at seven different frequencies were investigated. Recording was done with unipolar leads from frontal, central, occipital and temporal regions on the left and right side. In patients with multiple sclerosis the cortical responses to all these stimuli had lower amplitude than in healthy subjects, and the reponses to stroboscopic stimulation were also abnormal in the group of patients. Different clinical signs related to various defects of sensory functions showed a high correlation with electrophysiological anomalies. Non-linear discrimination analysis was carried out using 13 variants (the amplitudes were calculated from peak to peak and correlation coefficients were calculated between identical regions on the left and right side) comparing the group of patients with the control group. Using this method it was possible to establish the correct diagnosis in all cases of multiple sclerosis and 85% of healthy subjects could have been included into the asymptomatic group. Since the methods used in these investigations are easy and can be easily automated the authors think that they could be very useful in the clinical diagnosis of multiple sclerosis.

Acoustic Stimulation↗