Antonio Fernández-Bouzas

Relationship of specific EEG frequencies at specific brain areas with performance.

THIS study shows that incorrect responses are preceded by different EEG characteristics than correct responses, and that these differences appear in specific brain regions that participate in each particular task. EEGs were recorded in children during three different tasks: color discrimination (CDT), verbal working memory (VWM), and word categorization task (WCT). EEG segments previous to the presentation of the stimulus were analysed. Incorrect responses were preceded by lower EEG power values at 7.8 Hz in posterior temporal and right parietal leads in CDT, 8.59 and 9.36Hz in frontal areas in VWM, and 10.72 Hz in the left hemisphere in WCT. In the former task > 1.56 Hz power in frontal areas prior to an incorrect response was also observed.

Specific EEG frequencies at specific brain areas and performance.

In this study it was shown that in adults, the frequency characteristics of EEG preceding stimuli that were followed by incorrect responses were different from the characteristics of EEG preceding stimuli that were followed by correct responses. In the recording during three different tasks that explore different neuronal networks, higher values of current preceding incorrect performance in those areas directly related to the task were found in frequencies within the delta (1.56 and 3.12 Hz) and beta bands (13.26, 14.04, 14.82, 15.6, 17.16 and 17.94 Hz), suggesting that these frequencies signal inhibition. Frequencies within the alpha band (9.36 and 12.48 Hz) showed greater energy preceding correct responses in task-specific areas, supporting previous results observed in children.

EEG Coherences in Patients with Brain Lesions

EEG coherence between all pairwise combinations of the 10/20 system was studied in two groups: control subjects and patients with space-occupying brain lesions. Coherence was separately computed for the delta, theta, alpha and beta bands. Comparisons between both groups showed highly significant differences in all bands. In the patients with lower coherence values, these differences were mainly in the alpha band. When intra-hemispheric coherences between controls and patients with left hemispheric lesions were compared, significant differences were observed only in the left hemisphere. Comparisons between controls and patients with lesions in the right hemisphere also showed significant differences only in the injured hemisphere. In patients, paired t tests between the values of the intra-hemispheric coherence in the left hemisphere and the corresponding values in the right hemisphere demonstrated that lower coherences were confined to the damaged hemisphere. Our conclusion is that in the presence of lesions disrupting cortex and adjacent white matter the coherence between this area and the remaining cortical areas is lower than normal due to impairment of the fibers that connect the damaged area with the rest of the brain.

Frequency source analysis in patients with brain lesions

SummaryIn a previos study (Harmony et al. 1993) we observed that the volume of lesions was correlated only with delta power, while the volume and density of edema showed a significant correlation with theta and alpha power, suggesting two independent origins of activity in the delta and theta bands in patients with space-occupying lesions. Our goal in this paper is to show, through a different technique, in a narrow band spectral analysis, that brain lesions are characterized by activity in the delta domain and that edema is better correlated with activity within the theta range. Frequency source analysis based on the Maximum Likelihood (ML) test for rejection of isotropicity was applied to the EEG at rest of 36 patients with space-occupying intracranial lesions. The ML test was rejected at frequencies below 1 Hz and in the low range of the delta rhythm in 31 patients. The origin of the equivalent dipoles at these frequencies was within the volume of the lesion in 27 patients. In IS patients out of 19 with vasogenic edema the ML test was rejected at frequencies in the theta range. The equivalent dipoles at these frequencies were all within the volume of the edema.

Chapter 41 Sources of EEG activity during a verbal working memory task in adults and children

Publisher Summary In recent years, procedures that allow the identification and visualization of electroencephalographic (EEG) sources, within the brain, have been described in the chapter. It has also been shown that, previous to the stimuli, power and current values at specific EEG frequencies are necessary to perform correctly in three different tasks. These specific frequencies are required at those cortical areas that are directly related to the task: (1) prefrontal areas in a verbal working memory (WM) task, (2) posterior temporal and right parietal areas in a color discrimination task, and (3) Brocas area in a word categorization task. These observations have led to the conclusion that specific EEG frequencies play a particular role in neural processing, supporting another conclusion that oscillations in neural networks may be not simply a by-product of the activity of the neuronal networks, but may have a functional significance in the brain functioning. This chapter explains the task related EEG changes produced during a verbal WM task in young adults. A sample of school-age children performing the same task has also been studied. It is well known that at rest the EEG frequency content of children is different from adults. In children, EEG changes during task performance have been rarely reported.

Epileptic Encephalopathy in Children with Risk Factors for Brain Damage

In the study of 887 new born infants with prenatal and perinatal risk factors for brain damage, 11 children with West syndrome that progressed into Lennox-Gastaut syndrome and another 4 children with Lennox-Gastaut syndrome that had not been preceded by West syndrome were found. In this study we present the main findings of these 15 subjects. In all infants multifactor antecedents were detected. The most frequent risk factors were prematurity and severe asphyxia; however placenta disorders, sepsis, and hyperbilirubinemia were also frequent. In all infants MRI direct or secondary features of periventricular leukomalacia were observed. Followup of all infants showed moderate to severe neurodevelopmental delay as well as cerebral palsy. It is concluded that prenatal and perinatal risk factors for brain damage are very important antecedents that should be taken into account to follow up those infants from an early age in order to detect and treat as early as possible an epileptic encephalopathy.

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.

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.