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Abstract
In Attention Deficit Hyperactivity disorder (ADHD), fMRI studies show asymmetric alterations: widespread hypoactivation in anterior cortical areas and hyperactivation in some posterior regions, and the latter is considered to be related to compensatory processes. In Posner’s attentional networks, an important role is attributed to functional interhemispheric asymmetries. The psychophysiological Attention Network Test (ANT), which measures the efficiency of the alerting, orienting, and executive networks, seems particularly informative for ADHD. Potentials related to ANT stimuli (ANT-RPs) have revealed reduced cognitive potential P3 in ADHD. However, there are no studies associated with asymmetry of ANT-RPs. In the present study, conducted with 20 typically developing boys and 19 boys with ADHD, aged 11–13 years, the efficiency of the three Posner’s networks regarding performance and amplitude asymmetries in ANT-RPs was evaluated according to the arithmetic difference of these parameters between different cue and target presentation conditions. The results were correlated to Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) scores. Regarding accuracy and intraindividual variation in reaction time, ADHD subjects showed lower efficiency of executive and alerting network, and this effect was correlated with DSM. Regarding alerting network, ANT-RPs in ADHD did not have the right-side amplitude prevalence in the temporal regions, which was observed in controls. In all ANT conditions, significantly higher asymmetries were observed in ADHD than in controls in the occipital regions 40–200 ms after target onset. Their amplitude in ADHD subjects was inversely proportional to DSM scores of inattentiveness and directly proportional to accuracy and efficiency of the executive network. The results suggest impaired alerting and executive networks in ADHD and compensatory occipital mechanisms.
Highlights
Attention Deficit Hyperactivity disorder (ADHD) is one of the most prevalent cognitive disorders, occurring in approximately 5% of children [1], and is characterized, according to the American Psychiatric Association [2, 3], by two symptom dimensions, related to inattention and hyperactivity with impulsivity
Among the other significant differences observed between groups (Table 1), highlights are the efficiency of the executive network regarding AC (-0.06 ± 0.06 in controls higher than -0.11 ± 0.08 in ADHD, p = 0.04), and the efficiency of the alerting network (0.18 ± 0.06 in controls lower than 0.30 ± 0.15 in ADHD, p = 0.007), and the efficiency of the executive network (0.19 ± 0.08 in controls lower than 0.29 ± 0.15 in ADHD, p = 0.018) regarding IVRT
In the group with all 39 subjects, a strong correlation was observed between the total DSM score and the efficiencies of the alerting and executive networks (r = 0.62 and r = 0.54, respectively), and a moderate correlation was observed with the efficiency of the orienting network (r = 0.48) concerning IVRT (Table 2)
Summary
Attention Deficit Hyperactivity disorder (ADHD) is one of the most prevalent cognitive disorders, occurring in approximately 5% of children [1], and is characterized, according to the American Psychiatric Association [2, 3], by two symptom dimensions, related to inattention and hyperactivity with impulsivity. In the psychophysiological model for estimating attention known as Posner’s attentional networks [10,11], the executive and alertness functions are segregated as parts of a multidimensional attentional system divided in at least three neural systems, which: (a) maintain vigilance after a phasic change in alertness (“alerting” network) evoked by a warning signal; (b) orient to sensory events by modality or location (“orienting” network); and (c) drive and monitor perception and action by top-down control (“executive” network) These networks can be tested simultaneously using the Attention Network Test (ANT), which is an adaptation of previously developed experimental stimulus-reaction paradigms to test alertness and orientation of the covert attention by cueing, as well as to estimate interference of target information in conflict resolution based on flanker congruency [12]). A user-friendly ANT version [13] has shown impaired efficiencies of the executive [14,15,16,17] and the alerting networks [15, 17], with higher RT and/or IVRT in ADHD subjects
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