Neonatal States of Consciousness

1. Awake State

PMA Range: 30-32 weeks

Characteristics:

• Eyes open: The primary indicator that the baby is awake is the presence of open eyes.
• EEG Patterns: At 30-32 weeks PMA, the EEG shows a mostly continuous, low-voltage background. This pattern reflects an immature neural system that is still developing connectivity and regulation.
• Reactivity and Synchrony: Reactivity (how the brain responds to stimuli) and synchrony (how brain waves are coordinated) may vary depending on age and maturity. These aspects continue to mature after 32 weeks PMA.
• Development of Higher Amplitude: As the neonate reaches 35 weeks PMA, the EEG background shows higher amplitude with a more diverse range of frequencies, marking the brain's growing ability to process and integrate information.
• Movement and Respiration: An irregular respiratory pattern and movement artifact are often seen during this state, confirming that the baby is awake and active.

2. Active Sleep (similar to REM in adults)

PMA Range: 30-38 weeks

Characteristics:

• Eyes Closed: In the active sleep state, the baby’s eyes remain closed, and the baby is in a sleep phase similar to REM sleep in adults.
• Movements and Respiration: Eye movements are common, and there may be irregular breathing or brief episodes of apnea (temporary cessation of breathing). Some body movements may also be seen.
• EEG Patterns: The EEG during active sleep is characterized by continuous theta to delta activity, which is slower, high-amplitude brain waves. As the neonate matures, faster frequencies (such as mixed alpha or beta waves) begin to appear starting around 38 weeks PMA.
• Lateral Eye Movements: Lateral eye movements are frequently seen, which are best observed in the left occipital (LOC) and right occipital (ROC) EEG leads. These movements distinguish active sleep from quiet sleep.
• Absence of Movement Artifact: Unlike the awake state, active sleep is free from significant movement artifact, making the EEG tracings cleaner.

3. Quiet Sleep

PMA Range: 30-38 weeks

Characteristics:

• Eyes Closed with Minimal Eye Movements: In quiet sleep, the baby’s eyes remain closed with very few eye movements. Respirations are more regular compared to the active sleep state.
• Transitions: Neonates transition from awake to active sleep and then into quiet sleep. The sleep cycle is typically divided 50/50 between active and quiet sleep.
• Trace Discontinu: At 30-32 weeks PMA, quiet sleep is characterized by a **trace discontinu** pattern, which consists of bursts of activity with interburst intervals (IBIs) of low amplitude (less than 25 microvolts). These intervals typically last for less than 15 seconds.
• Trace Alternans: Around 34 weeks PMA, the trace discontinu pattern evolves into **trace alternans**, where the interburst intervals have higher amplitude (greater than 25 microvolts), indicating greater maturity in the sleep architecture.
• Slow Wave Sleep: By 38 weeks PMA, quiet sleep transitions into slow-wave sleep, a deeper, more mature sleep state where the EEG shows a predominance of slow delta waves.

Transition Periods

Before 28-30 weeks PMA, neonates do not show distinct sleep states. The EEG is largely discontinuous and unreactive. As the brain matures, these states become more defined, but early transitions can sometimes be unclear. Periods of indeterminate sleep (transitional states) are more common and may be particularly noticeable in neonates with brain injuries, such as those suffering from hypoxic-ischemic encephalopathy (HIE).

Key Differences Between Discontinu and Alternans

• Discontinu: The **interburst interval (IBI)** is less than 25 microvolts, and the EEG is characterized by bursts of activity with low-amplitude intervals. This pattern is typical for younger neonates (around 30-32 weeks PMA).
• Alternans: The **IBI** is greater than 25 microvolts, and the interburst intervals become more distinct. This pattern represents a more mature form of quiet sleep and is seen in neonates around 34 weeks PMA and older.