Study of interhemispheric coherence on healthy adults

Abstract

EEG coherence allows correlation between different brain areas to be ascertained by analyzing the mutual relationship between two EEG signals across different frequency bands. As this constitutes a normalized value for the power of a given frequency, it is independent from signal amplitude oscillations 1,2 Such a property makes coherence a relatively safe method for comparing groups of individuals in as far as differences in EEG powers do not impact estimated coherence values 3 . Reduced coherence between two regions is probably indicative of their decreased functional correlations. Ordinary coherence can be calculated between two cerebral electrodes, whether they be placed in the same hemisphere or in homologous areas, by means of a mathematical formula dividing the cross spectrum of these two channels by the product of self spectrum for each of these channels, as illustrated in the formula below:The Co value between two electrodes ranges from 0 to 1, where 1 denotes maximum correlation. When correlation is very low or null, the value approaches 0. Thus, coherence represents a measure of cortical interconnectivity. Studies concerning coherence have shown that coherence between closely-placed electrodes is determined mainly by local connections excited by intracortical interneurons (Martinotti and short axoned stellate cells), whereas between distant electrodes such coherence is determined by long axonal connections 4,5,6 . These two compartments compete with one another, influencing the same neuronal population in an alternate manner.The objective of the current investigation was to study the inter-hemispheric coherence between homologous areas in healthy individuals in the 20-50 year age bracket. METHODA total of 190 tests were carried out on individuals with no neurological complaints, where subjects were submitted to digital EEG and then assessed. Subjects had no prior history of neurological problems such as traumatic brain injury, epilepsy, alcohol or drugs use and abuse, or clinical com- ABSTRACT -The interhemispheric coherence of electroencephalogram was studied in a group of healthy individuals in the age range of 20-50 years. The results showed higher coherence for all bands in parietal regions (P3-P4). It was observed that individuals with high values of coherence for a certain frequency band in a pair of electrodes also showed high values of coherence for other bands across other pairs of electrodes. No significant influence on interhemispheric coherence was found for age, gender or hand dominance. STUDY OF INTERHEMISPHERIC COHERENCE ON HEALTHY ADULTSKEY WORDS: coherence, adults, EEG quantitative, normal pattern. Estudo da coerência interhemisférica em adultos normaisRESUMO -A coerência inter-hemisférica do eletrencefalograma foi estudada em uma população de indiví-duos normais, na faixa etária de 20 a 50 anos. Os resultados mostraram maior valor de coerência para todas as bandas nas regiões parietais(P3-P4). Foi observado que em indivíduos com alto valor de coerência para determinada banda em um det...

Alpha band EEG coherence in healthy nonagenarians

“…We analyzed, in our study in 2007 3 , the interhemispheric coherence for the alpha band for eight pairs of electrodes distributed across the scalp, in normal individuals aged 20 to 50 years. The mean values found were 0.66 for P3 and P4, and 0.63 for O1 and O2.…”

“…Jorge et al 3 studied a population of normal adults and did not observe any influence from age, gender or manual dominance regarding interhemispheric coherence values, for any of the frequency bands evaluated.…”

“…This is done through examining the mutual relationship between two EEG signals for different frequency bands. Quadratic or ordinary coherence consists of measurement of the covariance of spectral power between two pairs of electrodes 1,2,3 . Because coherence is a normative value for the power of a given frequency, it is independent of the amplitude oscillations of the signal 4,5 .…”

Bromazepam changes performance during target shooting but does not affect the interhemispheric coupling in the theta rhythm of the electroencephalography

“…Also, the theta rhythm facilitates synaptic plasticity, has an influence on the reaction time, and is related to the increased attention (Buzsaki et al, 2004;Linkenkaer-Hansen et al, 2004;Womelsdorf et al, 2006). Neurophysiological analysis by EEG coherence provides evidence of coupling between cortical areas during the execution of the task (Babiloni et al, 2005;Kay et al, 2006;Jorge et al, 2007). Although the action of BDZs has been investigated with EEG analyses (Salles et al, 2006), bromazepam action is still poorly understood in the target shooting task as well as coupling strength between cortical areas at different preparation times in shooting tasks.…”

Estudo do eletroencefalograma em indivíduos sem déficits cognitivos e com 90 anos ou mais

“…Também chamada de coerência quadrá-tica ou ordinária é a medida da covariância da potência espectral entre 2 pares de eletrodos. , Anghinah et al 2005,Jorge et al 2007). …”