Measurements of coherence in eeg signal in brazilian people: a comparison of different consciousness states

Critically ill patients admitted to intensive care units require special care and the early diagnosis of the possible outcome of this coma is clinically important. Electroencephalographic signals are collected daily in critically ill patients and can be used to aid in the early diagnosis of neurological pathologies in such patients. Therefore, this study aimed to quantitatively describe the coherence values measured by the EEG signal of Brazilian individuals. The first group with comatose patients (N = 75), favorable (to live) or unfavorable (dying) outcomes, and various etiology. The second group was made by neurologically normal people, named the control group (N = 100). In addition, a number of statistical comparisons were made in order to verify the difference in coherence behavior according to the levels of consciousness. The coherence index of the comatose group is smaller than the control group. Besides, different hospitalization results, living or dying, as well as different etiologies, may be associated with particular values of cerebral coherence. It was observed that the etiology of coma does not influence the measured values of coherence in terms of diagnosis due to brain death, which may become a biomarker of this outcome. Another important consideration was that neurologically healthy patients did not present high values of cerebral coherence at all electrodes, as seen in the temporal region of the brain.

Electroencephalogram patterns with the presence of an unknown musical stimulus

The cerebral activity presents different behaviors in different situations and levels of consciousness, especially under musical stimulation. Signals of the central nervous system may disclose bioelectrical patterns, since listening to rhythmic sequences activates specific brain areas. In this paper, we analyze 42 neurologically normal Brazilian individuals, submitted to musical stimulation based on a procedure consisting of three different steps, during which the volunteer is kept with closed eyes. The first step is associated with the preliminary control silence period, without any stimulus, as the volunteer remains at rest. The second step consisted of unknown music stimulation. Finally, the third step involves post-music rest. Quantitative signal analysis computes the power spectrum time variations. Results point out stronger changes in gamma and high gamma waves (30 ­ 100 Hz). Even though the clinical rhythms (0 ­ 30 Hz) change throughout the whole period of the experiment, quantitative differences at gamma and high gamma bands are remarkably greater. Particularly, when comparing the initial silent period and the final post-stimulation silent one, bioelectrical differences are only highlighted by gamma and high gamma rhythms. In consequence, this paper points out that the EEG analysis of cognitive issues related to musical perception cannot disregard gamma and high gamma waves.

Analysis of electroencephalography brain rhythms in the reading process / Análise dos ritmos cerebrais de eletroencefalografia no processo de leitura

ABSTRACT Objective: To verify if, by three distinct quantifiers, the measured electroencephalographic signal at rest is different from the signal measured during a word reading situation, especially considering the faster rhythms, gamma and high-gamma, as it occurs in clinical rhythms (delta to beta). Methods: A total of 96 electroencephalographic signals measured from neurologically healthy volunteers were evaluated at two moments: resting and word reading. Each signal segment was measured by three quantifiers that separately assess normalized power, percent power, and right and left hemisphere coherence. The Mann-Whitney test was used to compare the results of the quantifiers in each brain range. Results: The gamma and high-gamma rhythms presented a more distinct behavior when comparing the analyzed moments (resting and reading) than the clinical rhythms. Conclusion: This finding contributes to the scarce literature on faster rhythms, which can contain information that is normally disregarded in neurological clinical practice.

RESUMO Objetivo: Verificar se, por meio de três quantificadores distintos, o sinal eletroencefalográfico medido em repouso é diferente do sinal medido durante o processo de leitura, especialmente considerando os ritmos rápidos, gama e supergama, assim como ocorre nos ritmos clínicos delta a beta. Métodos: Foram avaliados 96 sinais eletroencefalográficos medidos em voluntários neurologicamente saudáveis, em dois momentos: repouso e leitura de palavras. Cada trecho do sinal foi mensurado por três quantificadores que medem, de maneira isolada, a potência normalizada e a potência percentual, bem como a coerência entre os hemisférios direito e esquerdo. O teste estatístico de Mann-Whitney foi usado para comparar os resultados dos quantificadores em cada faixa cerebral. Resultados: Os ritmos gama e supergama apresentaram comportamento mais distinto entre os momentos analisados (repouso e leitura) que os ritmos clinicamente analisados. Conclusão: Esse achado contribui com a escassa literatura segundo a qual os ritmos rápidos podem conter informações que normalmente são descartadas na neurologia clínica.