Rett syndrome, EEG and the motor cortex as a model for better understanding of attention deficit hyperactivity disorder (ADHD).

Abstract

EEG data in Rett syndrome (RS) are quite often characterized by spikes over the central region (especially in sleep). Furthermore, there has been a recent observation of a prominent and peculiar theta (4-6/s) rhythm over the central region and vicinity. In view of the clinical phenomena of RS, it is pointed out that clinical and electrical findings are based upon hyperexcitability of the motor cortex (or a state of motor cortex dyscontrol). States of dyscontrol (disinhibition) are caused by deficits in higher cortical functions. It is reasonable to assume a primary dysfunction for the frontal lobe which is also smaller in size than other cerebral regions. The behavioral (motor) disturbance in RS can be easily explained as the expression of disturbed prefrontal/premotor function with special effect on the "syntax of action". It is further theorized that such a state of fronto-motor cortex uncoupling may also exist in attention deficit hyperkinetic disorder (ADHD) even though there is hardly any structural CNS impairment in that condition. A presumed "lazy frontal lobe" is likely to react favorably to the stimulation provided by methylphenidate (a therapeutic effect which should not be viewed as paradoxical).