The development of electrocortical activity in the fetal and neonatal guinea pig.

We have developed techniques for chronic recording of electrocortical activity in the fetal and neonatal guinea pig with subsequent power spectral analysis. Thirty-four unanesthesized, unrestrained pregnant Hartley guinea pigs were studied 1 to 14 days following surgical procedures. Twelve neonatal animals instrumented during the first week of life were studied at 3 to 30 days. Spontaneous, undifferentiated electrocortical activity was recorded from the youngest fetuses studied, with high-voltage slow activity appearing at 50 days' gestation. Cycling electrocortical activity and sleep spindles could be observed in the late-term fetal and neonatal animals, with rapid eye movements and behavioral state defined in the latter. Power spectral analysis demonstrated more predominant delta activity, faster beta frequencies, and better-developed sleep spindles in the neonatal animal as compared to the fetus.