BIT-MAPPED SOMATOSENSORY-EVOKED POTENTIALS IN THE FRAGILE-X SYNDROME

Middle-latency somatosensory evoked potentials (MLSEPs) were recorded from 19 scalp electrodes in ten male patients with the fragile X (fraX ) syndrome and nine normal controls. One fraX patient was found presen ting the so-called ''giant'' MLSEPs with an amplitude of N60 of about 60 mu V and of 40 mu V after stimulation of the right and left median nerves, respectively. Tapping of the right hand, in the same patient, induced the appearance of left parietal evoked EEG spikes. These findi ngs further support the already suggested similarity between the epile ptic picture of several fraX patients with that of the benign childhoo d epilepsy with centrotemporal spikes. Color mapping of the MLSEPs rec orded in the remaining nine patients, when compared with the control g roup, showed an abnormally large N30 over the frontal regions, togethe r with an increase in amplitude of P27, over the parietal areas, and o f N60 and P100 which also presented abnormal field distributions, bein g represented preferentially over the frontal regions. These data coul d suggest the existence of a cortical dysfunction mostly involving the frontal lobes (supplementary motor area, in particular) in the fraX s yndrome which could support many behavioral changes usually observed i n these patients.