Ontogeny of cortical and subcortical electroencephalographic events in unrestrained neonatal and infant rats.

We have devised a method of stereotaxic implantation of electrodes in cortical and subcortical sites in neonatal and infant rats and subsequently recording from these animals as they move about freely. We studied the development of the EEG recorded from these cortical and subcortical sites in animals ranging in age from 1 to 84 days and analyzed the EEGs both visually and by power spectral analysis via a fast Fourier transform algorithm. The animals survived the procedure with less than 5% overall mortality. Although of very low voltage and very irregular in appearance, EEG activity was present in all sites at 1 day of age. There was gradual increase in synchrony, organization, and voltage until 12 to 14 days when an adult pattern appeared.