Unusual EEG theta rhythms over central region in Rett syndrome: considerations of the underlying dysfunction.

In 10 female patients (age 2-26 years) with clinical evidence of Rett Syndrome (RS), unusual and prominent rhythmical theta activity (4-5/sec or 5-6/sec) proved to be the outstanding EEG feature. This pattern was present in waking state and/or sleep. When it was noted in the waking state, the localization (vertex, central region and vicinity) and blocking responses to active or passive movements suggested a slow equivalent of Rolandic mu rhythm (in two patients associated with a posterior 10-12/sec alpha rhythm). In sleep, rhythmical theta activity was either Rolandic or more diffuse, sometimes independently occurring with central spikes. The prominent rhythmical 4-5/sec or 5-6/sec activity and its relationship to Rolandic mu rhythm suggest a dysfunction of the motor cortex in RS. This would be congruent with the frequent observation of central spikes. EEG evidence of motor cortex dysfunction might be helpful in the understanding of this enigmatic disorder and conducive to the following hypothesis: RS is characterized by motor cortical dyscontrol due to primary frontal lobe dysfunction. The usefulness of EEG, however, is limited to insights into the (secondary) motor-cortex dysfunction.