Decreased resting gamma activity in adult attention deficit/hyperactivity disorder

Objectives: To delineate task-free gamma activity in adult ADHD and healthy control subjects based on high-density EEG recordings. Relationship of gamma activity with symptom severity was also examined, since gamma activity is considered to be an index of network functions in the brain that underlie higher-order cognitive processes.
Methods: Spontaneous EEG was recorded in adult ADHD subjects (N = 42; 25 methylphenidate-naïve and 17 on methylphenidate treatment) and controls (N = 59) with eyes open. EEG absolute power gamma was investigated in the gamma1 (30.25–39 Hz) and gamma2 (39.25–48 Hz) frequency bands.
Results: Gamma1 and gamma2 activity was diminished in ADHD compared with healthy control subjects. The difference between ADHD and controls was the most pronounced in the right centroparietal region for both gamma1 and gamma2. Inverse associations were found between gamma1 and gamma2 activity and ADHD symptoms in centroparietal scalp regions.
Conclusions: Gamma activity is reduced in adult ADHD, and the reduction has a predominantly right centroparietal distribution. Our findings are consistent with childhood ADHD literature with respect to diminished posterior gamma activity in patients, which may reflect altered dorsal attention network functions. Gamma abnormalities might provide a link between neurophysiological functioning and neuropsychological deficiencies, thereby offering an opportunity to investigate the neurobiological mechanisms that underlie the clinical symptoms of ADHD.

研究目的：基于高密度脑电图（high-density EEG）记录，刻画成人注意缺陷多动障碍（ADHD）患者与健康对照受试者在无任务状态下的伽马振荡（gamma activity）特征；同时探讨伽马振荡与症状严重程度的关联，因伽马振荡被认为是支撑高阶认知过程的大脑网络功能的量化指标。
研究方法：对成人ADHD患者（N=42；其中25例未使用哌甲酯（methylphenidate），17例接受哌甲酯治疗）及健康对照受试者（N=59）开展睁眼状态下的自发脑电图记录。本研究针对伽马1（gamma1，30.25~39Hz）与伽马2（gamma2，39.25~48Hz）两个频段的脑电图绝对伽马功率展开分析。
研究结果：相较于健康对照受试者，ADHD患者的伽马1与伽马2振荡水平均出现减弱。两类频段的组间差异在右侧中央顶叶区域最为显著。在中央顶叶头皮区域，伽马1、伽马2振荡水平与ADHD症状呈负相关。
研究结论：成人ADHD患者的伽马振荡水平降低，且该降低主要分布于右侧中央顶叶区域。本研究关于患者后部伽马振荡减弱的发现与儿童ADHD相关文献结果一致，该现象或反映背侧注意网络（dorsal attention network）功能异常。伽马振荡异常或许可搭建起神经生理功能与神经心理缺陷之间的关联桥梁，为探究ADHD临床症状背后的神经生物学机制提供新的研究路径。