Spontaneous cortical activity and auditory evoked responses were recorded with a whole-scalp 122-channel neuromagnetometer from 4 patients after left-hemisphere dominant herpes simplex encephalitis and associated memory disorders. Spontaneous activity of one patient contained periodic sharp waves over the left hemisphere; the background activity was attenuated. The sources of periodic sharp waves clustered close to the sources of auditory evoked fields in the temporal lobe. In controls, dominant rhythmic activity over the parieto-occipital region had spectral maximum at 10.6 +/- 0.6 Hz; in patients the dominant rhythmic activity peaked at 8.6 +/- 1.8 Hz. The suppression of the parieto-occipital activity in eyes-open versus eyes-closed condition was smaller in patients than in controls. The patients' peak spectral frequency was correlated with neuropsychological tests reflecting deficient attentional capacity. The observed changes probably reflect decreased subcortical control of the cortical electric activity.