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Updated: Jun 16, 2026
Infant Auditory Processing and Event-related Brain Oscillations
Published on: July 1, 2015
Developmental appearance and disappearance of cortical events and oscillations in infant rats
Adele M H Seelke1, Mark S Blumberg
1Department of Psychology and Delta Center, Program in Behavioral and Cognitive Neuroscience, The University of Iowa, Iowa City, IA 52242, USA. amseelke@ucdavis.edu
Insights
Early rat neocortical activity is more complex than previously thought, with distinct patterns like cortical sharp potentials (CSPs) and gamma bursts (GBs) emerging soon after birth, challenging earlier timelines.
Area of Science:
- Neuroscience
- Developmental Neuroscience
- Computational Neuroscience
Background:
- Previously, organized neocortical activity in infant rats was believed to begin around postnatal day 11 with delta waves.
- Recent discoveries, including spindle bursts (SBs) and slow activity transients (SATs), indicate earlier cortical activity.
- This study investigates the emergence and characteristics of early neocortical activity patterns.
Purpose of the Study:
- To document the appearance, disappearance, and transient expression of cortical events and oscillations in infant rats (postnatal days 5-13).
- To identify and characterize novel forms of early cortical activity beyond known patterns.
- To explore the developmental trajectories and state-dependency of these early neurophysiological events.
Main Methods:
- EEG recordings were performed in unanesthetized, head-fixed infant rats (P5-P13) using 16-channel laminar silicon electrodes.
- Recordings were taken from frontal, parietal, and occipital cortices.
- Analysis focused on identifying and quantifying distinct electrophysiological events and oscillations.
Main Results:
- Three distinct cortical activity patterns were identified: slow activity transients (SATs), cortical sharp potentials (CSPs), and gamma bursts (GBs).
- CSPs showed an inverted-U developmental trajectory, peaking at P9, while GBs increased in prevalence and duration from P5 to P13.
- SAT prevalence decreased steadily, and both CSPs and GBs were more frequent during sleep.
Conclusions:
- Early neocortical development in rats exhibits a richer variety of activity patterns than previously recognized.
- SATs, CSPs, and GBs represent distinct neuronal activity patterns with unique developmental trajectories.
- These diverse neurophysiological patterns likely reflect the evolving local structure and connectivity of the developing neocortex.
Abstract:
Until recently, organized and state-dependent neocortical activity in infant rats was thought to commence with the emergence of delta waves at postnatal day (P)11. This view is changing with the discovery of several forms of cortical activity that are detectable soon after birth, including spindle bursts (SBs) and slow activity transients (SATs). Here we provide further evidence of surprisingly rich cortical activity patterns during early development and document, in P5-P13 rats, the appearance, disappearance, and transient expression of three cortical events and oscillations. EEG activity in frontal, parietal, and occipital cortices was recorded in unanesthetized, head-fixed subjects using 16-channel laminar silicon electrodes and Ag-AgCl electrodes. In addition to SATs, we identified two novel forms of activity: cortical sharp potentials (CSPs) and gamma bursts (GBs). SBs were not observed in these areas. CSPs, defined as discrete, biphasic events with a duration of 250 ms, exhibited an inverted-U developmental trajectory with peak prevalence at P9. In contrast, GBs, defined as brief bursts of 40-Hz activity, increased steadily in prevalence and duration from P5 through P13. The prevalence of SATs decreased steadily across the ages tested here. Furthermore, both CSPs and GBs were more likely to occur during sleep than during wakefulness. Because SATs, CSPs, and GBs exhibit different developmental trajectories and rates of occurrence, and can occur independently of each other, they appear to be distinct patterns of neuronal activity. We hypothesize that these diverse patterns of neurophysiological activity reflect the instantaneous local structure and connectivity of the developing neocortex.
