Academic journal article Iranian Journal of Psychiatry

Neurocognitive Profile of Children with Attention Deficit Hyperactivity Disorders (ADHD): A Comparison between Subtypes

Academic journal article Iranian Journal of Psychiatry

Neurocognitive Profile of Children with Attention Deficit Hyperactivity Disorders (ADHD): A Comparison between Subtypes

Article excerpt

According to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), attention deficit and hyperactivity disorder (ADHD) is defined as a neuro -developmental disorder that is characterized by impairment in the levels of attention, disorganization and/or hyperactivity-impulsivity and it occurs in about 5% of children and about 2.5% of adult population (1, 2). In this group of children, inattention and disorganization characteristics are involved in inability to maintain tasks, seeming not to listen and losing tilings, and the hyperactivity-impulsivity characteristic involves in over activity, fidgeting, inability to stay seated, dismpting other's activities and inability to wait more than what is expected for their age (1). Moreover, in childhood, there are overlaps between ADHD and other disorders like oppositional defiant disorder and conduct disorder (1, 3, and 4). In adulthood, ADHD leads to impairments in social, academic and occupational functions (1, 4-6).

It lias been suggested that there are deficits in underlying cognitive processes related to attention, organization and hyperactivity-impulsivity in children with ADHD (1, 7). One of the most accepted explanations of characteristics of children with ADHD is the deficit in executive function (EF) domain which is assumed to be facilitated by the frontal lobes and is defined as neuro-cognitive processes that maintain an appropriate problem solving ability to achieve future goals (8-10). Executive function domains that are assumed to be related to ADHD symptoms are response inhibition or working memory or overall weakness in executive control (7, 8, 10-12). As noted in Willcutt et al., this explanatory theory is based on the observation that reveals damages to the prefrontal lob may lead to distraction, hyperactivity or impulsivity along with deficits on EF tests (13). As defined in DSM-5, ADHD is divided to three subtypes: predominantly hyperactive/impulsive (ADHD-H), predominantly inattentive (ADHD-I) and combined (ADHD-C) (1). According to the previous studies, these three subtypes are distinguished from one another based on inattention symptoms, related features, motor function, demographic variables and reaction to stimulant medications (14-21). Some authors proposed that not only there are differences between children with ADHD and typically developing children in executive functions domains, but also these differences are observed between ADHD subgroups (mostly between inattentive and combined) to some extent, mostly on amount of response inhibition(18, 22-25).

Based on Barkley's model, ADHD-C subtype is related to deficits in executive functions, but there is no executive function deficit for ADHD-I subtype (7). This model is supported by subsequent studies, in which executive dysfunction is observed in ADHD-C subtype but not in ADHD-I subtype (26, 27).

In some studies it has been shown that the ADHD-C subtype groups have impairments in planning and cognitive flexibility domains in comparison with ADHD-I (28), but this finding has not been repeated in later studies (29). It is also found that there are more weaknesses in the ADHD-C subtype in comparison to the ADHD-I subtype in response inhibition domain and verbal fluency (29, 30).

In another study, discrepancy in executive functions of children with ADHD was investigated based on subtypes and gender. This study showed that the ADHD-C subtype had differences in cognitive flexibility and inhibition in comparison to normal controls, but there were no differences between ADHD-I subtype and controls. Moreover, two ADHD subtypes did not show any differences (27). Other studies on this subject revealed no significant differences between the ADHD subtypes in the executive function domain (31-33).

Given these inconsistent findings, there is a necessity for more investigation on this issue. Therefore, the present study was designed to examine the differences between the ADHD subtypes in executive function task in comparison with themselves and with the normal group. …

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