Age-related changes of cortical excitability in subjects with sleep-enhanced centrotemporal spikes: a somatosensory evoked potential study

Middle-latency somatosensory evoked potentials (SEPs) of particularly large amplitude (giant) have been reported in subjects with benign childhood epilepsy with centrotemporal spikes (BECT) and in normal children, which usually show significant age-related changes. However, the mechanisms by which age modifies the appearance of centrotemporal spikes and giant SEPs in these children, are not known. The characteristics of SEPs were studied in a group of 18 subjects (10 males and 8 females, aged 7.1-17.2 years) with sleep-enhanced centrotemporal spikes, with or without BECT and the results were compared with those obtained from a group of age-matched normal controls. Giant SEPs were recorded in 6 subjects and, in 3 of these, EEG spikes evoked by hand tapping were obtained also. No subjects with giant SEPs were found in subjects older than 12 years, and an age-related decrease in amplitude of giant SEPs as this age approached was observed. Moreover, at repeated SEP recordings, a clear trend towards a more important reduction in amplitude of giant SEPs over the temporal and parietal than over the central regions was evident. The study of EEG spikes evoked by hand tapping showed a striking similarity between the averaged evoked spikes and the main negative component of giant SEPs. It was also possible to observe that the spike negative peak recorded over the central areas always preceded the same component recorded over the parietal and temporal areas by 5-15 ms. Our study seems to support the idea that giant SEPs in subjects with centrotemporal spikes are generated by a complex mechanism different from that at the basis of the normal N60 component of SEPs; they also show peculiar age-related modifications which can be interpreted in terms of maturational changes of brain excitability/inhibition and probably constitute a tool for monitoring the clinical course of BECT, when present.