2003, Number 1
Los procesos de la atención y el electroencefalograma cuantificados en un grupo de pacientes con trastorno por déficit de atención
Reyes-Zamorano E, Ricardo-Garcell J, Galindo VG, Cortes J, Otero G
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Language: Spanish
References: 36
Page: 11-22
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ABSTRACT
The Attention Deficit Disorder (ADD) is a developmental and chronical disorder, characterized mainly by a decrease in attention. Difficulties in the inhibitory control (expressed through behavioral and cognitive impulsiveness) and also verbal and motor restlessness are characteristic in this disorder. They should appear at an early age (before 7) and be considered inadequate in regard to the patient’s age and expected level of development.Current research suggests that their attention spans are shorter than those of their peers because their greater deficit is found in the area of sustained attention.
Other symptoms of ADD are impulsiveness – hyperactivity, and it may be difficult to differentiate one from the other. The first one, impulsiveness, has been defined as acting without thinking, while the second one, hyperactivity, describes the excessive or inappropriate level of either verbal or motor activity. In school population, according to the DSM-IV, the prevalence of this disorder is 3-5%. It is the most frequent mental disease in childhood. The male/female rate may differ according to the sample that is being studied. In a clinical sample it is common to find a 6:1 ratio, while in the general population it may only be 3:1.
In order to evaluate the attention process and the executive functions, many psychological tests have been created, and due to the clinical characteristics of ADD patients, these instruments have been incorporated to the different test batteries used in the evaluating process. One of these tests is the Continuous Performance Test (CPT), a psychological task that evaluates two corner symptoms of ADD: inattention and impulsiveness. It’s clinical usefulness has been proved through different studies.
On the other hand, the quantitative analysis of the electroencephalogram (EEG) has become a useful tool in the evaluation of this disorder. Using this technique, both, an increase in the theta band absolute and relative power, and abnormal excess in the alpha band in the anterior regions, have been reported.
CPT and EEG are both techniques commonly used in the ADD patient evaluation; nevertheless, no study has ever analyzed the possible correlation between them.
Therefore the goal of the present study was to analyze the correlation between CPT’s variables and the brain electrical activity.
The absolute power of the EEG’s delta, theta, alpha and beta bands, and the number of omissions, commissions, reaction time, response style and confidence index of the CPT, were correlated in a sample of 35 ADD patients with an average age of 10.49 years (S.D.=3.31). The 8 females and 27 males were clinically evaluated by a specialist to meet DSM-IV criteria for ADD. All the EEG values (absolute power) were normalized by logarithmic transformation, and due to the fact that both variables tend to decrease while age increases, partial correlations controlled for age, were calculated. The statistic software SPSS 10 was used.
The EEG of the patients was characterized by a predominant activity in the delta, theta and alpha bands, especially in the slow bands. Delta activity was more important in frontopolar and lower frontal regions; theta activity was dominant in the upper frontal, and central regions, and the alpha band activity was more evident in posterior regions. In the temporal zone, the power of these three bands was almost equivalent. These results are similar to the characteristic EEG pattern of ADD.
All the psychological measures, except the confidence index, showed statistically significant correlations.
The number of commissions, the reaction time, and the response style indicator had more correlations with the theta activity of the central, upper frontal and parietal regions. The remaining variable, the number of omissions, showed a significant correlation with the alpha band in the frontopolar, lower frontal and right temporal posterior areas.
Thus, statistically significant correlations were grouped in two patterns: 1) omissions showed a positive correlation with the alpha band activity in temporal and frontal inferior areas, 2) all the remaining psychological variables correlated positively (except commissions which correlated negatively) with generalized theta activity. These results suggest that, in this sample of ADD patients, such brain activity patterns may be the electroencephalographic marker that identifies a poor CPT performance.
Just as well, it could be said that the presence of theta activity in the resting EEG in the noted areas tempers with the ability of the anterior and posterior attentional networks to appropriately solve the task. This is better observed in the reaction time measure. While almost all the correlations are positive (when the electrical activity increases the number of errors also increase), the number of commissions correlated negatively with the brain electrical activity (when the electrical activity decreases, the number of errors increases and vice versa). This is explained by the conscious effort of the patient to solve the task correctly. In order to avoid making mistakes, the patient increases the reaction time trying to have more time to correctly process the stimuli information, but because of his own attention deficit he can’t take advantage of this strategy and ends up losing information. If we consider the response style indicator that allows us to evaluate the speed/accuracy relationship, then the significant correlation values (almost exclusive) of this variable with the theta band support the previous affirmation. Finally all the patient did was to increase the number of omissions, but at the same time the number of commissions decreased. Thus, an inattentive profile became evident.
Even though the brain electrical activity recording and the application of the CPT were done at different times, the results support the fact that the absolute power of the remaining EEG, in the delta, theta and alpha bands, specially in the theta band, is related with a poor performance in most of the CPT’s variables analyzed. It is suggestive also of a relationship between the EEG and the different cognitive processes measured by the CPT.
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