Hippocampal theta in the newborn rat is revealed under conditions that promote REM sleep

Karl Karlsson, Mark S. Blumberg*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

35 Citations (Scopus)


Hippocampal theta activity, a high-amplitude, slow (4-12 Hz) oscillation that occurs in a variety of behavioral contexts, is thought to emerge in infant rats only after 1 week of age. However, we report here that unanesthetized 2- and 4-d-old rats with electrodes implanted in the CA1 field of the hippocampus and tested in thermoneutral conditions exhibit theta activity. Moreover, this infant theta is characterized by the same neuronal bursting pattern and power spectrum that characterize theta in adults. Simultaneous measures of behavior and neck muscle tone indicated that bouts of theta occurred predominantly during periods of muscle atonia (with or without concurrent myoclonic twitching), indicative of REM sleep. In contrast, sharp waves were accompanied by startles (i.e., simultaneous and vigorous movement of all four limbs). These findings underscore the need for comprehensive in vivo investigations of the pharmacology, neural substrates, and behavioral correlates of hippocampal field activity in neonates.

Original languageEnglish
Pages (from-to)1114-1118
Number of pages5
JournalJournal of Neuroscience
Issue number4
Publication statusPublished - 15 Feb 2003

Other keywords

  • Behavior
  • Hippocampus
  • Muscle tone
  • Myoclonic twitching
  • REM sleep
  • Sharp waves
  • Startle
  • Temperature


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