Sedated sleep and sleep deprivation are commonly used methods to increase the diagnostic yield of the electroencephalogram (EEG), especially in the evaluation of people with epilepsy, but the rate of activation achieved by them is controversial, as is the issue of whether it is sleep itself, or sleep deprivation which is responsible for their alleged efficacy. We retrospectively studied the EEGs of epileptic patients, examined in our laboratory, who, after having undergone an inconclusive initial routine recording, had then been examined with a second recording. This was after either: (1) sleep deprivation with evidence of drowsiness in the recordings, (2) sleep deprivation without drowsiness (indicative of the effect which sleep deprivation per se has in eliciting abnormal patterns), or (3) drug-induced sedation. The activation rates found were (1) 22.5%, (2) 24% (22.6% for sleep deprivation collectively, regardless of the presence or not of subsequent drowsiness) and (3) 27% respectively. Only the sleep deprivation rate was statistically different from the 9.6% increased rate of abnormal patterns elicited by the simple repeating of a second routine recording, while the rate of drug-induced sleep was not. Although, sleep deprivation appeared to be more effective as an activating method of EEG compared with sedated sleep, no conclusions could be drawn about which stage of sleep, wakefulness or drowsiness, is primarily responsible for the method's efficacy.

The EEGs of 13,560 patients have been reviewed in order to determine whether abnormal findings, epileptiform or not, have a hemispheric dominance. We have included outpatients and hospitalized patients as well. Eight hundred and thirty-five EEGs had generalized abnormal findings, and 414 EEGs had lateralized abnormal findings. The EEGs of 322 patients (77.7%) had a left predominance, and those of 92 patients (22.3%) had a right predominance, of abnormal findings. A strong left predominance has been noted for the epileptiform discharges, i.e. 128 (79%) vs. 34 (21%). These results raise the possibility that the left hemisphere may be more vulnerable to nosological processes.