Abstract

REYES ZAMORANO, Ernesto et al. Event-related potentials and commorbidity in a group of teenagers with Attention Deficit Hiperactivity Disorder. Salud Ment [online]. 2008, vol.31, n.3, pp.213-220. ISSN 0185-3325.

Attention deficit hyperactivity disorder (ADHD) is a neuro-developmental disorder clinically characterized by three core symptoms: deficits in attentional processes, failure in inhibitory control -usually expressed through behavioral and cognitive impulsiveness-, and motor and verbal restlessness. Deficit in attentional resources is the main alteration in patients with this disorder. Attention can be considered as a neurocognitive state of neural preparation that precedes both perception and action. Attention focalizes consciousness in order to filter the constant flux of sensorial information, solve competence between stimuli for parallel processing and recruit and activate cerebral regions necessary to accomplish appropriate responses. Event-related potentials (ERPs) are a technique that has proven useful in the gathering of valuable information in the study of ADHD. One of the most studied ERPs is the P300 component. The most robust finding in the P300 research in ADHD is a decrease in the amplitude of the component in patients when compared to normal controls. This finding is usually interpreted as an evidence for a deficit in attention. ADHD usually presents commorbidity with several disorders; research shows that up to 87% of the children with ADHD present commorbidity with another disorder, up to 60% has either a behavioral or affective disorder commorbid with ADHD. Due to the wide range of disorders that are usually associated with this entity, it is useful in the research of commorbidity to use dimensional diagnostics, that is, a patient with ADHD may have commorbidity with an externalized disorder (EXT) (i.e. oppositionist defiant disorder); an internalized (INT) disorder (i.e. anxiety or affective disorder); or both an externalized and an internalized disorder (MIX). Commorbidity may have important implications in the electrophysiology of ADHD since no homogeneous results have been evident in the scarce research on the subject. Taking into account these considerations, the following experiment was designed in order to answer the question: Patients with the same main diagnostic, ADHD, but different commorbidities (INT and MIX) show different psychophysiological patterns of activation, as measured by ERPs to a continuous performance task? Sixteen patients diagnosed with ADHD by a specialist were recruited. Diagnosis was corroborated by a semi-structured interview, K-SADS-PL-MX, eight of them with an externalized comorbid (EXT) disorder, and eight of them with at least two comorbid disorders, one externalized an one internalized (MIX). A control group (CON) of eight normal subjects with no psychiatric diagnostic and matched by sex was also recruited. All subjects were between 13-16 years old with no history of Central Nervous System damage and normal IQ in the Weschler Intelligence Scale for Children. Brain electrical activity was recorded in the 19 derivations of the 10-20 international system while subjects executed a continuous performance task (CPT). Comparisons of behavioral data between groups showed some significant differences. A one-way ANOVA found differences between groups in the mean reaction time to the first part of the CPT and in the number of false positives in the second part. Electrophysiological data was analyzed with a non-parametrical multivariate test of permutations. When comparing responses to the frequent stimulus with responses to the infrequent, statistically significant differences were found in every subject; such differences share the topography and latency characteristics of the P3b component. When comparing the amplitude of this component between the groups, only two statistically significant differences were found. First, the EXT group presented a greater amplitude of the component elicited by the first part of the task in a latency of 425 to 445 msec in the parietal region of the medial line than the CON group. Second, also in response to the first part of the task, the amplitude of the CON group was bigger than that of the MIX group in a latency between 355 and 420 msec in the left temporal anterior region. No other comparison yielded significant results. When comparing between groups, mean reaction time to the first part of the task was the only behavioral variable that adequately distinguished control and patients. Even though controls executed significantly faster, they maintained the same efficacy as no differences were found in the number of errors or correct responses. This result is not surprising due to the fact that long reaction times usually denote inattention and so the fact that both groups of patients execute slower than the controls may be interpreted as a sign that, in spite of having different commorbidities, inattention is still a common problem in every patient of the sample. On the second part of the task, only the number of false positives showed statistically significant differences. However, in a posterior analysis of the data, it was evident that such differences were only between the EXT and the CON groups, with the EXT group presenting significantly more errors. False positives, especially on the second part of the task, are a measure of behavioral inhibition. Failure in inhibitory control is one of the three main symptoms of ADHD. However, some have proposed it as the main characteristic of the disorder. Analysis of the electrophysiological response to the first part of the task showed characteristic profiles of execution for each group. First, the P300 component was smaller in amplitude in the MIX group than in the control group and, even though differences were significant only in one derivation (T3), several other electrode sites more typically associated with the P300 component (C3, C4, P3, P4 and Pz) showed similar tendencies that did not reach statistical significance. Second, EXT patients had greater amplitude of the same P300 component in Pz than CON subjects. This result may seem to contradict most of the research on ADHD and P300. Nevertheless, considering the behavioral data, specially that no differences in correct responses were found between patients an controls, it is posible to assert that the greater amplitude of the component represents an overactive compensation in attentional circuits, necessary in the EXT group in order to execute at the same level of non-ADHD subjects. The results of this study present with information on a poorly reasearched subject: comorbidity and electrophysiology on ADHD.

Keywords : Event-related potentials; attention deficit hyperactivity disorder; externalized commorbidity and P300.