Increased mirror overflow movements in ADHD are associated with altered EEG alpha/beta band desynchronization

Abstract

Children with ADHD show developmentally abnormal levels of mirror overflow-unintentional movements occurring symmetrically opposite of intentional movements. Because mirror overflow correlates with ADHD behavioral symptoms, the study of disinhibition in motor control may shed light on physiologic mechanisms underlying impaired behavioral/cognitive control. This is a case-controlled study of EEG recording from 25 children with ADHD and 25 typically developing (TD) controls performing unilateral sequential finger tapping, with overflow movements measured using electronic goniometers. Consistent with previously published findings, children with ADHD showed increased mirror overflow as compared with TD peers. EEG findings revealed less lateralized alpha modulation (event-related desynchronization; ERD) and decreased magnitude of beta ERD in ADHD; both alpha and beta ERD reflect cortical activation. Moderation analysis revealed a significant association between beta ERD and overflow, independent of diagnosis; and an equivocal (p = .08) effect of diagnosis on the relationship between alpha ERD and overflow, with a significant effect in children with ADHD but not TD children. These results suggest two mechanisms involved with mirror overflow: one reflected in beta ipsilateral to the intentional movement and relevant to both children with ADHD and controls, and the other seemingly more specific to ADHD (alpha, contralateral to movement).

Keywords: EEG; moderation analysis; motor control; sensory-motor rhythm.

Figure 1.. The Duke equidistant electrode layout.

The darkened electrodes were used in analysis.

Figure 2.. Task-related spectrograms measured in the right central (RC) regions during left-handed finger tapping.

Darker colors indicate greater magnitude of ERD. All bands were measured from 1.5 to 3 sec following tapping onset. The alpha band was measured in the pass-band of 10–13 Hz; low beta at 14–17 Hz (no group differences either in ipsilateral or contralateral ROIs); and beta in 18–28 Hz.

Figure 3.. Alternative causal models for the effect of diagnosis on the relationship between physiology (as indexed by ERD) and behavior (mirror overflow movements).

In panel (a), the effect of ADHD diagnosis occurs solely upstream of the physiology indexed by ERD. In panel (b), the effect of ADHD diagnosis occurs upstream of the physiology (as evidenced by group differences in distribution of ERD values), but also has a moderating effect on the link between physiology and behavior.

Figure 4.. Children with ADHD showed more overflow on average than controls.

This was true in both (a) right (p = 0.02) and (b) left-handed finger tapping (p = 0.006).

Figure 5.. Topographical plot of ERD associated with left-handed finger tapping.

The greatest degree of ERD is in bilateral motor regions. White stars indicate the channels which were used for statistical analyses. The first column is restricted to left-handed finger tapping; the second, to right-handed finger tapping; and the third averages the two task conditions.

Figure 6.. TD controls showed greater alpha asymmetry (distance from zero) than children with ADHD (p=0.02).

Further, the TD group showed an alpha asymmetry that was statistically different from zero (p=0.04), whereas the ADHD group did not (p=0.2).

Figure 7.. Scatterplot of (a) alpha and (b) beta ERD by overflow, by group.

There was a significant correlation in the ADHD group but not the TD group between alpha ERD and mirror overflow. There was a significant correlation within the TD group but not the ADHD group between beta ERD and mirror overflow.