Elsevier

Biological Psychiatry

Volume 46, Issue 12, 15 December 1999, Pages 1690-1697
Biological Psychiatry

Original Articles
Age-related changes in quantitative EEG in attention- deficit/hyperactivity disorder

https://doi.org/10.1016/S0006-3223(99)00042-6Get rights and content

Abstract

Background: Attention-deficit/hyperactivity disorder (ADHD) in children and adolescents is characterized by excessive restlessness and an extremely poor concentration span, resulting in impulsive and disruptive behavior. Clinical observation of ADHD in adults suggests that the hyperactivity component is diminished although the impulsive type behaviors remain apparent. EEG studies of children and adolescents with ADHD have reported significantly higher levels of low frequency activity (predominantly theta) and lower levels of beta activity than normal controls.

Methods: We examined the relationship between the age-related changes reported in clinical observation and changes in EEG activity occurring in a group of ADHD patients ranging in age from 6 to 42 years. Quantitative EEGs were obtained from the midline sites of 25 children, 25 adolescents and 25 adults diagnosed with ADHD, and compared with those of age matched normal controls.

Results: Theta activity was elevated in the ADHD groups across all age groups compared with the normal controls. The extent of the reduction in relative beta activity in the ADHD groups compared to normal controls decreased with increasing age.

Conclusions: Given that the hyperactivity component in ADHD reduces with age while the impulsivity component remains, these data, in ADHD, suggest that decreased beta activity may be linked to hyperactivity and increased theta activity to impulsivity.

Introduction

Historically, many diagnostic labels have been used to describe what is currently termed attention-deficit/ hyperactivity disorder (ADHD). The essential diagnostic criteria for the disorder, however, remain unchanged, and include developmentally inappropriate levels of impulsive, hyperactive and inattentive behaviors. It is these behaviors that affect almost every area of daily functioning. ADHD is now recognized as a common childhood disorder and the DSM IV (American Psychiatric Association 1994) estimates that 3–5% of school-age children are affected. In adolescence and adulthood, data and information on prevalence is not available.

Until recently, it was assumed that children outgrew ADHD by the time they reached puberty as a result of developmental changes. Clinical observation now suggests that as children and adolescents with ADHD mature, the number and intensity of their symptoms reduce but they remain impaired.

According to Barkley (1990), the primary characteristics of inattention, behavioral inhibition and hyperactivity persist into the adolescent years in 70–80% of children with ADHD. Poor organization, behavioral inhibition and difficulties in task completion present as the predominant symptoms, along with problems relating to discipline, antisocial behavior, poor performance at school and problems with peer relationships. Barkley (1991) reported that adolescents with ADHD display significant impairments in attention, impulsivity and overactivity, along with academic achievement, social competence and behavioral adjustment. It is also reported that during adolescence there is a higher risk for associated comorbid disorders including conduct disorder, antisocial disorder and oppositional defiant disorder (Wender 1995a). Studies carried out over the past two decades (e.g., Brown and Borden 1986), have demonstrated that although there is a reduction in the degree of hyperactivity, in general, the impulsive and inattentive behaviors continue.

Studies assessing the clinical presentation of ADHD in adulthood have identified a range of symptoms thought to constitute an adult form of the condition. Hechtman et al (1981) identified 3 categories of outcome in adults with the disorder. First there are adults who essentially function normally. Second, there are adults who continue to display significant problems with concentration, social integration, emotional and impulse control, that impact negatively on their work, relationships and self esteem, leaving them anxious, emotionally labile and irritable. There is also a third group of adults who have serious psychiatric problems including depression, suicidal ideation, antisocial behavior and substance abuse. Barkley (1990) suggests that the level of hyperactivity diminishes in terms of its impact on social or academic function although the manifestation of impulsive behavior increases. It has been reported (e.g., Serfontein 1994, Weiss and Hechtman 1993) that adults with ADHD continue to present with attention problems, often choosing to work in occupations requiring little or no attention to detail. According to Wender (1995b), adults with ADHD continue to present with attentional difficulties that tend to manifest themselves in personal relationships and academic pursuits, and they often report problems with short term memory, distractibility and impulsivity. The symptoms of the disorder in adults may present more as internalized feelings of tension, restlessness and distraction from focused thought.

The development of quantitative electroencephalogram (qEEG) analysis has led to the study of age-related changes in EEG activity. In a study by Matousek and Petersen (1973), EEG was collected at rest on a group of normal children and adolescents using absolute and relative powers in 6 frequency bands. Results indicated that there was a linear decrease in delta (1.5–3.5 Hz) activity with age, an increase in theta (3.5–7.5 Hz) and alpha 1 activity (7.5–9.5 Hz) from 4 to 8 years of age followed by a decrease, an overall increase in alpha 2 activity (9.5–12.5 Hz), and a slight decrease in beta activity (12.5–25 Hz) with age. In a study by John et al (1980) examining EEG as a function of age, it was concluded that EEG development was linear in nature. A longitudinal study by Benninger et al (1984) demonstrated that as theta activity decreased, alpha activity increased. Gasser et al (1988a) demonstrated a differential rate of maturation in each of the frequency bands (delta, theta, alpha, beta) that differed topographically. It was also reported that there was a change of dominant frequency from fast alpha activity to theta activity from 6–16 years. In summary, these studies have provided evidence that EEG activity changes systematically as a function of age.

In recent years qEEG has been used in the diagnosis of ADHD in young children and may prove useful as a diagnostic adjunct in adolescents and adults where diagnosis is difficult due to existing comorbid conditions. The most commonly reported finding in electrophysiological studies of children with ADHD is increased low frequency activity (predominantly theta) compared with age-matched normal controls. Mann et al (1992) reported increased theta and decreased beta 1 in a sample of 25 boys diagnosed with ADHD without hyperactivity. Using discriminant analysis, they demonstrated that low frequency activity (theta) discriminated the target group with greater than 80% accuracy. Using the ratio of theta to beta to account for maturational and intrasubject variability, Lubar (1991) reported a significant increase in frontal theta/beta ratio in boys with attention problems and without hyperactivity. This difference was reduced in the posterior region. Matsuura et al (1993), in a World Health Organization (WHO) study of several western pacific countries, reported that children with ADHD had more delta and fast theta activity and fewer alpha waves than age matched controls and a group of children with deviant behaviors.

Satterfield and Cantwell (1974) reported a more effective response to methylphenidate in a group of ADHD children with excessive theta activity. Further, Satterfield et al (1984) reported that increases in theta activity are age dependent. Children with ADHD aged above 90 months produced significant increases in theta activity with decreased theta activity in children with ADHD younger than 90 months. Callaway et al (1983) reported significantly decreased beta activity in hyperactive children compared to age-matched normals. This finding was consistent with data reported by Dykman et al (1982) and Matsuura et al (1993).

Research into qEEG changes with maturation led to the development of two neurophysiological models of ADHD. The Maturational Lag model, proposed by Kinsbourne (1973), states that in ADHD there is a delay in the maturation of the CNS, resulting in behaviors that are typically seen in younger children. This has been noted in clinical observation of children with the disorder. Further, some aspects of the disorder, such as hyperactivity, tend to disappear with age. Event Related Potential studies by Satterfield (1973) found that children with ADHD have significantly lower amplitudes and longer latencies as are typically seen in younger children.

The Central Nervous System Hypoarousal model, proposed by Satterfield et al (1972), states that children with ADHD have a low level of CNS arousal, leading them to continuously seek new environmental stimuli, and manifesting in their high level of distractibility and hyperactive behaviors. Treatment with psychostimulants has the effect of reducing the excessive motor activity in patients with ADHD, providing support for this model. Other studies (e.g., Satterfield and Dawson 1971) have reported that skin conductance levels in a significant proportion of children with ADHD are lower than those of normal children.

Much of the existing research has identified maturational lag or CNS hypoarousal as the underlying cause of ADHD. Although these models have initiated extensive research, they have failed to clarify the aetiology of the disorder.

The overall aim of this study was to investigate the age-related changes in qEEGs in a group of ADHD patients ranging in age from 6–42 years compared with normal controls. Further, we proposed that changes in the qEEGs of subjects diagnosed with ADHD might reflect some of the age-related behavioral changes reported in the clinical setting.

Section snippets

Subjects

Fifty children (6–11 years), 50 adolescents (13–17 years) and 50 adults (20–42 years) participated in the study. Twenty-five children, 25 adolescents and 25 adults were diagnosed ADHD. All subjects were diagnosed by several professionals. Children and adolescents were diagnosed with ADHD if they met the criteria of the Diagnostic and Statistical Manual of Mental Disorders (Fourth edition), after clinical assessment by a pediatrician, clinical interview by a psychologist, and using their scores

Results

Independent groups t-tests were used to compare the ADHD and control groups on age. No significant differences were found between children, adolescents and adults with ADHD and their respective control groups.

Discussion

Previous research examining electrophysiological measures in children and adolescents with ADHD compared with normal controls have generally reported an increase in theta activity Mann et al 1992, Matsuura et al 1993 and a decrease in beta activity (Callaway et al 1983). Similar findings were obtained in the present study, with children and adolescents with ADHD producing more theta power and less beta power compared with age matched controls. This study however, extended on these findings by

Acknowledgements

The authors wish to acknowledge the contribution of Drs. Simon D Clarke and Mark Kneebone for providing the independent diagnostic assessments in this research.

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