اختلالات عملکرد عصب روان شناختی در بزرگسالان مبتلا به نقص توجه/بیش فعالی

Neuropsychological deficits in children diagnosed with attention deficit/hyperactivity disorder (ADHD) have been well documented utilizing various neuropsychological tests. Only recently has research begun to examine if similar deficits are present in adults with ADHD. A neuropsychological testing battery was constructed that assessed verbal learning and memory, psychomotor speed, and sustained attention — all demonstrated to be deficient in individuals with ADHD. Fifty-six self-referred nonmedicated adults with a DSM-IV diagnosis of ADHD and 38 normal comparison adults participated. ADHD adults demonstrated verbal and nonverbal memory deficits and decreased psychomotor speed compared to normal controls. Differences between ADHD and normal adults were not documented on traditional measures of executive functioning. A pattern of results emerged whereby ADHD adults' performance, particularly with regard to psychomotor speed, became more impaired as task complexity increased. This study's results largely corroborate similar neuropsychological testing results in ADHD children and recent ADHD adult findings, and support a frontal lobe dysfunction hypothesis of ADHD.

A large body of research literature has examined neuropsychological functioning in children diagnosed with attention deficit/hyperactivity disorder (ADHD). Much of this research has assessed specific domains of impairment by comparing the performance of ADHD children to normal children on neuropsychological tests. These studies have shown that ADHD children perform more poorly than non-ADHD children on neuropsychological tasks measuring sustained attention Douglas, 1983 and Seidel & Joschko, 1990, executive functioning Chelune et al., 1986 and Shue & Douglas, 1992, motoric inhibition Iaboni et al., 1995 and Oosterlaan & Sergeant, 1996, and verbal learning and memory Loge et al., 1990, Seidman et al., 1995 and Tannock et al., 1993. These deficits have been consistent and replicable across most studies and are widely acknowledged to be the core neuropsychological deficits in children with ADHD (Barkley, 1997b). Barkley (1997a), defines executive functions as those neuropsychological processes that permit or assist the person with self-regulation. With Barkley's review of the literature, he concludes that most of the seemingly disparate abilities found to be discrepant in ADHD children (i.e., (1) motor coordination and sequencing; (2) working memory and mental computation; (3) planning and anticipation; (4) verbal fluency and confrontation communication; (5) effort allocation; (6) application of organizational strategies; (7) internalization of self-directed speech; (8) adherence to restrictive instruction; and (9) self-regulation of emotional arousal) fall within the domain of executive functions in the field of neuropsychology and are considered to be mediated by the frontal cortex, particularly the prefrontal lobes. The aforementioned areas of neuropsychological impairment have associations with frontal lobe functions Hynd et al., 1991, Lezak, 1976 and Shue & Douglas, 1992. Consequently, ADHD causality has been conceptualized in at least three different ways, as (1) frontal lobe dysfunction Castellanos et al., 1996 and Hynd et al., 1990, (2) delayed frontal maturation functioning (Chelune et al., 1986), and (3) subcortical-frontal motor subsystems dysfunction Castellanos et al., 1994 and Giedd et al., 1994. Further evidence for attributing ADHD impairments to the frontal lobe comes from studies of frontal lobe-damaged adults who demonstrate similar behavioral and cognitive symptomatology as ADHD patients Gualtieri & Hicks, 1985 and Mattes, 1980. More recently, several neuro-imaging studies have shown abnormalities in the prefrontal cortex of ADHD patients who were participating in tasks requiring executive functioning Castellanos et al., 1996 and Hynd et al., 1990. For most of its history, ADHD was conceptualized as a childhood disorder. Thus, the neuropsychological functioning of ADHD children has been well documented; however, little is known about the neuropsychological functioning of adolescents and even less is known about the more recently defined diagnosis of adult ADHD. With regard to adolescents, two studies have been conducted that document neuropsychological deficits similar to those found in younger ADHD children Fischer et al., 1990 and Seidman et al., 1997. Specifically, ADHD adolescents demonstrated impaired performance on neuropsychological tests that assess attention Fischer et al., 1990 and Seidman et al., 1997, executive functioning Fischer et al., 1990 and Seidman et al., 1997, impulse control (Fischer et al., 1990), and verbal learning (Seidman et al., 1997). These findings in adolescent ADHD individuals support the supposition that neuropsychological deficits do not attenuate over time. These studies support the conceptualization of ADHD as a disorder with chronic, consistent deficits that persist beyond the elementary school years. ADHD is now conceptualized as a disorder with a lifelong course Shaffer, 1994 and Wender, 1995. Approximately 30–50% of patients continue to meet diagnostic criteria for ADHD in adulthood Klein & Mannuzza, 1991 and Weiss & Hechtman, 1993. Assessing whether or not adult ADHD patients suffer from similar neuropsychological deficits as children and adolescents is a logical next step and helps address at least three theoretical questions. First, one explanation for the neuropsychological deficits found in ADHD is that the brain maturation of ADHD children is delayed (Chelune et al., 1986). Demonstration of concordant neuropsychological deficits in ADHD children and ADHD adults would seem to refute this explanation since the maturational brain development of an adult is complete. A second theoretical issue is that ADHD is conceptualized as a developmental disorder with symptoms that persist across the life span (Weiss & Hechtman, 1993). Neuropsychological differences documented in ADHD children should be, in theory, similar to those documented in ADHD adults. Lastly, a controversy remains regarding the validity of ADHD as a disorder of adulthood. Indeed, a reliable set of diagnostic criteria has yet to be delineated for a diagnosis of adult ADHD. Objective measures, such as neuropsychological tests, that document differences between ADHD and non-ADHD adults in neurocognitive functioning provide further evidence of ADHD as a valid disorder of adulthood. As ADHD has become recognized as a chronic and pervasive disorder, researchers began to assess areas of neuropsychological functioning in ADHD adults Epstein et al., 1997, Epstein et al., 1998, Holdnack et al., 1995, Horner, 1996, Riordan et al., 1999 and Seidman et al., 1998. Many early studies of adults only required target adults to have a history of ADHD in childhood without assessing for adult symptomatology Jenkins & Cohen, 1998 and Klee et al., 1986. While a childhood history of ADHD symptoms must be documented, the presence of symptoms in adulthood is required for an adult ADHD diagnosis (Wender, 1995). Only a few studies have been published that assessed a sample of adults with current ADHD symptoms using a standard battery of neuropsychological tests with demonstrated discriminability in childhood and adolescent populations Holdnack et al., 1995 and Seidman et al., 1998. Holdnack et al. used Wender Utah Criteria (Wender, 1995) to identify 25 ADHD adults and 30 non-ADHD adults. All participants completed a neuropsychological battery that assessed sustained attention, psychomotor speed and integration, executive functioning, response inhibition, and verbal learning. The only differences found between ADHD and normal adults were on measures of verbal learning on a list-learning task and psychomotor speed. More recently, Seidman et al. identified 64 ADHD adults using DSM-III-R criteria and compared their neuropsychological performance to that of 73 non-ADHD control subjects. A similar pattern of deficits to that of Holdnack et al. was found with slower psychomotor speed and impaired verbal learning. Seidman et al. also demonstrated differences between groups on auditory sustained attention. As with the Holdnack et al. study, differences were not documented on traditional measures of executive function or response inhibition. Riordan et al. (1999) assessed the neuropsychological functioning of 21 adults with ADHD based on DSM-IV criteria, 19 adults with ADHD and comorbid affective disorder, and 15 normal control subjects. Via factor analysis, the authors identified eight neuropsychological summary scales. Adults with ADHD were found to have relatively intact verbal reasoning and visual memory but demonstrated impaired performance on measures of verbal memory, motor and processing speed, visual scanning, and auditory and visual distractibility. While these three studies documented some specific neuropsychological deficits, no study demonstrated the pervasive pattern of neuropsychological differences that has been documented in ADHD children and adolescents. In order to better understand the neurocognitive functioning of adults with ADHD, the current study examines the performance of nonmedicated ADHD adults compared to normal controls on a traditional battery of neuropsychological tests designed to assess neurocognitive deficits documented in the childhood ADHD literature. We hypothesize that ADHD adults would perform statistically significantly worse on a battery of neuropsychological measures designed to assess executive functions believed to be impaired in this population. These measures include tests of verbal and nonverbal memory, fluency of speech and reading, visuomotor tracking, abstract behavior/shifting sets, psychomotor speed, and sustained attention.