Eeg Del Trastorno Por Déficit De Atención

APORTES DEL ELECTROENCEFALOGRAMA CONVENCIONAL Y EL
ANÁLISIS DE FRECUENCIAS PARA EL ESTUDIO DEL TRASTORNO POR DÉFICIT DE ATENCIÓN. PRIMERA PARTE*

Josefina Ricardo Garcell**

SUMMARY
Attention deficit disorder (ADD) is a chronic developmental disorder, characterized mainly by: decrease in attention, cognitive and behavioral impulsiveness due to a weak inhibitory control, and motor and verbalrestlessness. According to the international taxonomy, all these symptoms must be evident by the age of 7, and inappropriate for the age or level of development of the patient. There are very few objective evaluation methods available, and if one bears in mind that ADD is considered as the result of a dysfunction in the Central Nervous System (CNS), and that the electroencephalogram (EEG) is adirect measure of brain performance, this seems like an adequate tool to evaluate this disorder. The contribution of traditional EEG to the research on ADD is controversial but most of the authors report the presence of frequent abnormal activity in the EEG of these patients. The most common abnormality is an increase in the slow activity but it has also been reported that they have a significantlyhigher percentage of epileptic activity than normal kids, which it is more evident during hyperventilation and photostimulation. Quantitative analysis of EEG, particularly in the frequency domain, opened new possibilities for the study of ADD. Among the abnormalities found with broad band spectral parameters (BBSP) the most frequent are: 1. increase in theta absolute power (AP) and relative power(RP), 2. increase in the theta/alpha and theta/beta coefficients, 3. non-specific decrease in the midfrequencies of the alpha and beta bands, 4. inter hemispheric abnormalities (power asymmetry and a reduction in the parietal– posterior temporal coherence, increase in the frontal–central regions coherence), 5. intra hemispheric (power asymmetry between the frontal-temporal and frontal–occipitalregions, increase in the frontal–temporal coherence and reduction in the frontal–occipital coherence). These findings have been explained by some as a maturational lag in the brain electrical activity development, while others believe them to be a deviation of it. This maturational lag means that the electroencephalographic abnormalities reported would be normal in a younger child, while a deviationof development would mean the presence of abnormal electrical patterns that would not be normal under any circumstance

at any age. A maturational lag may eventually disappear as the patient grows old, while a deviation in development is commonly believed to be a dysfunction of the CNS. Most BBSP studies in ADD have been done with the patient’s eyes closed, resting; nevertheless, open-eyesstudies have come up with very similar results. Abnormalities in the BBSP of different samples of ADD patients as those pointed out have been found in up to 85–90%. On the other hand, a great disadvantage of most EEG studies is the assumption of clinically homogeneous groups, but there is plenty of evidence suggesting that ADD may represent a heterogeneous population, with different underlyingelectrophysiological abnormalities. A recent study in Mexico City found different patterns in the BBSP results of 154 ADD patients: theta (20%) or alpha (22%) as the most significant activity, specially in the anterior and medial regions, increase in beta activity as the only abnormality (2%), increase in the slow activity specially delta (6%), non–specific abnormalities (25%), a pattern suggesting amaturational lag in the brain electrical activity development (10%) and without abnormalities in these measures (15%). The percentage of patients with normal EEG may account for the fact that some clinicians underestimate the value of these measures for the study of ADD. It is noteworthy that there is plenty of evidence that the patterns of maturational lag and deviation of brain electrical...