Absent movement-related cortical potentials in children with primary motor stereotypies

Abstract

The underlying pathophysiologic mechanism for complex motor stereotypies in children is unknown, with hypotheses ranging from an arousal to a motor control disorder. Movement-related cortical potentials (MRCPs), representing the activation of cerebral areas involved in the generation of movements, precede and accompany self-initiated voluntary movements. The goal of this study was to compare cerebral activity associated with stereotypies to that seen with voluntary movements in children with primary complex motor stereotypies. Electroencephalographic (EEG) activity synchronized with video recording was recorded in 10 children diagnosed with primary motor stereotypies and 7 controls. EEG activity related to stereotypies and self-paced arm movements were analyzed for presence or absence of early or late MRCP, a steep negativity beginning about 1 second before the onset of a voluntary movement. Early MRCPs preceded self-paced arm movements in 8 of 10 children with motor stereotypies and in 6 of 7 controls. Observed MRCPs did not differ between groups. No MRCP was identified before the appearance of a complex motor stereotypy. Unlike voluntary movements, stereotypies are not preceded by MRCPs. This indicates that premotor areas are likely not involved in the preparation of these complex movements and suggests that stereotypies are initiated by mechanisms different from voluntary movements. Further studies are required to determine the site of the motor control abnormality within cortico-striatal-thalamo-cortical pathways and to identify whether similar findings would be found in children with secondary stereotypies.

Keywords: EEG; motor control; motor stereotypies; movement-related cortical potentials.

Figure 1

Examples of MRCPs preceding voluntary arms movements in 3 patients (A) and one control (B). Temporal evolution of early and late MRCP over the electrode showing maximal MRCP is plotted. Scalp localization of the maximal MRCP is represented in blue.

Figure 2

Temporal evolution and scalp representations of averaged EEG preceding stereotypic events in four patients. There were no MRCPs preceding motor stereotypies in any of the subjects.

Figure 3

Examples of EMG patterns during mimicking of stereotypies by a healthy control, mimicking of stereotypies by a patients and actual involuntary stereotypies from the same patient. Four bilateral couples of muscles (R: right; L: left) are displayed for each example: anterior deltoid (AD), Biceps brachialis (Bic), extensor carpi radialis (ECR), and flexor carpi ulnaris (FCU).