Atypical EEG beta asymmetry in adults with ADHD.

BACKGROUND: Abnormal brain laterality (ABL) is well established in ADHD. However, its clinical specificity and association to cognitive and clinical symptoms is not yet understood. Previous studies indicate increased right hemisphere (RH) contribution in both ADHD and reading impaired samples. The current study investigates whether this ABL characteristic occurs in adults with ADHD absent comorbid language impairment. METHODS: EEG beta asymmetry was compared in 35 adult ADHD subjects and 104 controls during rest and active cognition. Group differences in beta asymmetry were then further evaluated for association to linguistic and attentional abilities, as well as association to beta asymmetry measures across different brain regions. RESULTS: Adults with ADHD showed pronounced rightward beta asymmetry (p=.00001) in inferior parietal regions (P8-P7) during a continuous performance task (CPT) that could not be attributed to linguistic ability. Among ADHD subjects only, greater rightward beta asymmetry at this measure was correlated with better CPT performance. Furthermore, this measure showed a lack of normal association (i.e., observed in controls) to left-biased processing in temporal-parietal (TP8-TP7) brain regions important for higher order language functions. CONCLUSION: Adult ADHD involves abnormally increased right-biased contribution to CPT processing that could not be attributed to poor language ability. This appears to also involve abnormal recruitment of LH linguistic processing regions and represents an alternative, albeit less effective, CPT processing strategy. These findings suggest different pathophysiologic mechanisms likely underlie RH biased processing in ADHD and reading impaired samples.

Familial clustering and DRD4 effects on electroencephalogram measures in multiplex families with attention deficit/hyperactivity disorder.

OBJECTIVE: The current study tests electroencephalogram (EEG) measures as a potential endophenotype for attention deficit/hyperactivity disorder (ADHD) by examining sibling and parent-offspring similarity, familial clustering with the disorder, and association with the dopamine receptor D4 (DRD4) candidate gene. METHOD: The sample consists of 531 participants (191 parents and 340 children) from 132 multiplex families with ADHD who participated in a larger genetics study. All members of the families underwent extensive assessment including semi-structured diagnostic interviews and EEG recording. RESULTS: Strong sibling similarity and parent-offspring correlations in EEG power emerged, suggesting high trait heritability. Increased theta power was observed among children with ADHD when compared with unaffected children, and there were no differences according to ADHD subtype. Within the parent sample, ADHD diagnostic status and ADHD subtype group differences emerged in the theta, alpha, and beta frequency bands. DRD4 effects for both parents and children were apparent in the beta frequency band and for children only in the theta frequency band. CONCLUSIONS: This study suggests that EEG measures are a promising avenue of study in the search for putative endophenotypes for ADHD, and that variability at the DRD4 gene may contribute to this endophenotype.

ADHD familial loading and abnormal EEG alpha asymmetry in children with ADHD.

OBJECTIVE: Abnormal brain laterality (ABL) is indicated in ADHD. ADHD and brain laterality are heritable. Genetic factors contributing to lateralization of brain function may contribute to ADHD. If so, increased ADHD family loading should be associated with greater ABL. Previous studies have shown increased rightward alpha asymmetry in ADHD. We tested whether this was more pronounced in ADHD children with increased ADHD family loading. METHODS: We compared EEG alpha asymmetry at rest and during the Conner's Continuous Performance Test (CPT) in ADHD children with and without ADHD affected parents, and replicated our findings in a second larger sample. The replication study additionally stratified the parent-affected sample by parental persistent versus non-persistent ADHD status, increased spatial resolution of EEG measures, and assessed low versus high-alpha. RESULTS: Study-1: the parent-affected group showed increased rightward asymmetry across frontal and central regions and reduced rightward parietal asymmetry during an eyes closed (EC) condition, as well as increasing rightward parietal asymmetry with advancing age during the CPT. Study-2 replicated these findings and further delineated influences of low versus high-alpha, recording site, and effects of parental persistent versus non-persistent ADHD status. CONCLUSION: Increased ADHD familial loading was associated with increased rightward frontal asymmetry. In contrast, increased rightward parietal asymmetry was associated with reduced ADHD family loading. Frontal results are consistent with an ADHD endophenotype. Parietal results suggest an ADHD adaptive trait prevalent with less ADHD family loading. Age effects indicate a unique developmental course among ADHD children whose parents have non-persistent ADHD.

Atypical alpha asymmetry in adults with ADHD.

INTRODUCTION: A growing body of literature suggests atypical cerebral asymmetry and interhemispheric interaction in ADHD. A common means of assessing lateralized brain function in clinical populations has been to examine the relative proportion of EEG alpha activity (8-12 Hz) in each hemisphere (i.e., alpha asymmetry). Increased rightward alpha asymmetry has been associated with ADHD-like traits such as reduced reward responsiveness, a lack of inhibition toward aversive experience, and increased approach behaviors, and previous work has indicated increased rightward alpha asymmetry in children with ADHD. The current study explores whether increased rightward alpha asymmetry is also evident in adults with ADHD. METHOD: We assessed low (8-10 Hz) and high (10-12 Hz) alpha asymmetry in adults with ADHD (n=29) versus controls (n=62) during baseline and cognitive activation conditions for nine homologous electrode pairs along the anterior-posterior axis. RESULT: Seven results emerged (p<.05) showing increased rightward alpha asymmetry in adults with ADHD. This occurred in three specific electrode pairs across two testing conditions, and five of six results occurred in the lower alpha band. Finally, post hoc analysis indicated that increased rightward alpha asymmetry was generally associated with greater numbers of ADHD symptoms--with a possible parietal association for inattentive and a fronto-temporal association for hyperactivity symptoms. CONCLUSIONS: Increased rightward alpha asymmetry previously observed in children with ADHD appears to be a developmentally persistent feature of ADHD.

Cortical activity patterns in ADHD during arousal, activation and sustained attention.

OBJECTIVE: The goal of the present study is to test whether there are Attention-Deficit Hyperactivity Disorder (ADHD)-related differences in brain electrical activity patterns across arousal, activation and vigilance states. METHOD: The sample consists of 80 adults (38 with ADHD and 42 non-ADHD controls) who were recruited for a family study on the genetics of ADHD. Patterns of cortical activity were measured using electroencephalography (EEG) during baseline and sustained attention conditions and compared according to ADHD diagnostic status. Cortical activity was examined separately for the first, middle, and last 5-min of the sustained attention task to assess whether patterns differed over time and according to ADHD status. RESULTS: In frontal and parietal regions, patterns of activation in the alpha (8-10 Hz) range differed according to ADHD status, indicating increased cortical arousal among ADHD subjects. Beta power (13-14 and 17-18 Hz) also differed between ADHD and controls, indicating increased cortical activation is associated with ADHD. Behavioral performance on the sustained attention task did not differ significantly by diagnosis. EEG correlates of cognitive performance differed significantly ADHD diagnosis and were primarily in frontal regions. Brain activation patterns recorded during the sustained attention task suggest that the ADHD group exhibited significantly increased cortical activation at the end of the task when compared to controls. CONCLUSIONS: Adults with ADHD may have different neural organization primarily in frontal regions which results in the need for continually high levels of cortical activation to maintain sustained attention.

Rethinking a right hemisphere deficit in ADHD.

INTRODUCTION: Early observations from lesion studies suggested right hemisphere (RH) dysfunction in ADHD. However, a strictly right-lateralized deficit has not been well supported. An alternatively view suggests increased R > L asymmetry of brain function and abnormal interhemispheric interaction. If true, RH pathology in ADHD should reflect interhemispherically networked and overactivated functioning. The authors evaluated these assertions. METHOD: Four elements of lateralized brain function were measured: LH specialized, RH specialized, LH with interhemispheric processing (LH/IH), and RH with interhemispheric processing (RH/IH). Next, the authors tested their association with cognitive ability, psychiatric comorbidity, and sibling correlations in 79 children with ADHD. RESULTS: RH/IH processing was uniquely associated with other outcome measures. There were no associations for independent RH or LH function alone. CONCLUSION: Interhemispherically networked RH processing is critical in ADHD. In addition, lack of association between LH specialized processing and cognitive ability (especially for verbal cognitive tasks) supports increased RH mediation of task processing.