1. Neonatal EEG (0–4 weeks)

At birth, the EEG is characterized by immature, disorganized patterns that reflect the early stages of brain development. Neonates exhibit:

  • Diffuse Slowing: The brain's activity is marked by slow waves, including theta (4–7 Hz) and delta (0.5–4 Hz) waves, more pronounced and widespread than in adults.
  • Discontinuity: There is a lack of continuous brain activity, with periods of activity interspersed with periods of quietness.
  • Asynchrony: The electrical activity in the two hemispheres of the brain is often not synchronized, and they may not communicate effectively.
  • Minimal Reactivity: The brain's response to external stimuli is weak, and EEG patterns appear random with little to no immediate response to external stimuli.

Developmental Trends: The brain starts forming spontaneous rhythms and gradually increases in synchrony as the baby develops.

2. Infant EEG (1 month to 2 years)

As the baby moves into the infant stage, EEG patterns begin to show more development:

  • Increase in Frequency: The EEG shows higher frequency activity with theta waves (4–7 Hz) becoming more prominent, and activity becomes more continuous.
  • Emergence of Sleep Patterns: Distinct phases of sleep start to develop, including quiet sleep (non-REM) and active sleep (REM).
  • Maturation of Cortical Networks: The brain starts forming better-connected neural networks, leading to more synchronized brain activity.

Additional Changes: The brain begins to react more to external stimuli, though reactivity is still less developed compared to older children and adults.

3. Toddler/Preschool EEG (2–5 years)

During this stage, EEG characteristics further mature:

  • Transition to Theta and Alpha Waves: By age 2, theta rhythms become more pronounced. By age 4-5, alpha rhythms (8–12 Hz) begin to appear.
  • Increased Cortical Maturation: Better organized and synchronized activity begins to emerge, and the brain starts to show refined connectivity between regions.
  • More Defined Sleep Stages: Sleep patterns mature, including sleep spindles and K-complexes, along with deeper stages of non-REM sleep.

EEG Pattern Shifts: The brain shows less discontinuity, and the brain waves become shorter and more organized, reflecting improved efficiency in neural processing.

4. Childhood EEG (5–12 years)

By the time the child reaches school age, EEG patterns become more complex and closer to those seen in adults:

  • Mature Rhythmic Activity: Alpha (8–12 Hz) and beta (13–30 Hz) rhythms become more distinct, reflecting higher levels of brain activity and maturation.
  • Well-Defined Sleep Architecture: Sleep spindles and K-complexes become prominent, with more structured REM and non-REM sleep phases.
  • Increased Cortical Maturation: The brain continues developing efficient cortical networks, with better synchronization between brain regions.

Developmental Milestones: Alpha and beta activity becomes more prominent during awake states, and the EEG becomes increasingly responsive to cognitive tasks.

5. Adolescent EEG (12–18 years)

As the brain continues to mature, adolescent EEG patterns become almost identical to those of adults:

  • Adult-like Rhythms: The EEG now shows more complex patterns, including alpha, beta, and theta rhythms in response to various stimuli and tasks.
  • Increased Alpha Activity: Alpha rhythms dominate during relaxation and restful states, similar to adult EEG patterns.
  • Continued Maturation of Frontal Lobes: Higher cognitive abilities related to executive functions (planning, attention, self-regulation) become more prominent, influencing the EEG patterns.

6. Adult EEG (18+ years)

By adulthood, EEG patterns are well-defined and synchronized. Key features include:

  • Distinct Rhythmic Patterns: The EEG shows clear alpha, beta, theta, and delta waves corresponding to different states of consciousness (e.g., awake, relaxed, sleep).
  • Complex Cognitive Responses: Event-related potentials (ERPs) like the P300 appear, reflecting higher-order cognitive processing and response to stimuli.

Summary of EEG Development

  • Neonatal EEG: Immature, disorganized, slow, with minimal reactivity.
  • Infant EEG: Rhythmic and synchronized activity begins to emerge, with early sleep pattern development.
  • Toddler/Preschool EEG: Transition to theta and alpha rhythms, with more defined sleep stages and improved response to stimuli.
  • Childhood EEG: Alpha and beta rhythms become prominent, and EEG becomes closer to adult-like patterns.
  • Adolescent EEG: EEG patterns become nearly identical to adults, with continued maturation of cognitive processes.
  • Adult EEG: Clear, well-structured rhythms dominate, with distinct alpha, beta, theta, and delta waves.