Studies point to a systematic shift in various signatures of the EEG from infancy to adulthood, however there is no clear large scale longitudinal dataset for benchmarking.
The various development stages of the brain from newborn, infancy and adolescence are not simply a cognitive maturation but also marked by ‘sensitive periods’ with different functional characteristics and needs. Some suggest that an infant’s brain must be particularly suited for attachment and bonding with their caregiver and must therefore possess unique neural circuitry optimized for this task. Others suggest that adolescence is a sensitive period with a greater predisposition for exploration and risk taking. Certainly practical experience and studies from psychology seem to suggest as much. How does this reflect in the brain?
There have been various longitudinal studies across development using fMRI that suggest a fair bit of difference in connectivity and a great deal of intra-person variability. Changes in the EEG from infancy to adulthood has been less well studied. The majority of EEG studies with children have focused on trying to associate particular patterns of EEG activity with particular behaviors, targeting a particular age or stage of development. Nonetheless we were able to find a few studies that shed light on how the EEG signal varies according to different developmental stages.
Developmental changes in the EEG power spectrum
A study of ~4000 people from a clinical repository by Aurlien HG et al (in Clinical Neurophysiology, 2004) characterized alpha oscillations (based on peaks in power spectrum between 7 and 15 Hz) across age groups, finding that this characteristic was largely absent in EEGs from those under 10 and only occurred robustly after age 14.
Consistent with this, two studies have examined the occipital peak in “alpha” activity which in adults predominantly arises at ~10Hz, showing that while the alpha peak is absent, peaks are present at lower frequencies.
Firstly, Miguel Diego from University of Miami School of Medicine recorded the EEG from newborn infants (n=348) and found that many infants between 1 week and 1 month old exhibited a spectral peak around ~4Hz, although there was variability and some infants displayed no peak. By the time they had reached 3 months, the primary peak was at approximately 5Hz.
See related post Alpha Oscillations and Attention
In another study (Strogonova et al, 1999) with slightly older infants (n=154), Tatyana Stroganova and colleagues from Moscow State University of Psychology and Education found that this occipital peak was at an average of 6.24 Hz (+/- 0.45) in 8 month olds, shifting to an average of 6.78Hz (+/- 0.38) in children aged 11 months.
From Stroganova et al 1999
These findings, together with research from the adult literature about the inter-individual variability in the alpha peak, remind us that arbitrarily assigning frequency windows to specific wavebands can sometimes be misleading, especially from a developmental perspective. These lower frequency peaks may reflect oscillations in the signal that become increasingly fast over development and possibly serve the same purpose as the quintessential adult “alpha” oscillation. At this stage it is not clear how these peaks are related over development and also if they are specific to different regions over development. Large scale and systematic study is called for to understand this.
Changes in the P300
The P300 is another aspect of the EEG that shows developmental progression. The P300 is an increase in the EEG waveform ~300 ms after presentation of a sensory stimulus. In a detailed meta-analysis from 75 studies conducted by Rik van Dinteren and colleagues in the Netherlands, they found that the latency and amplitude of the auditory evoked P300 component varies according to the age of the participants in the study. In infants (younger than 10 years) and older participants (e.g. 60+) the latency of the P300 is generally longer (i.e. closer to 400ms), whilst the P300 amplitude seems to first increase and then steadily decrease over the lifespan. This suggests that we develop both speed and strength of response as we develop but then begin to lose it later as we age. It also illustrates a great deal of variability among age matched individuals, particularly in adulthood.
See related post Intra-person Variability in the EEG
Using infant EEG to measure clinical interventions.
Understanding the developmental trajectory of EEG activity in the infant brain becomes especially important when trying to use EEG as a marker of health or when trying to determine the effects of different clinical interventions. For example a study by Laura Cornelissen and colleagues from MIT used EEG to study the effect of anesthesia interventions in infants aged 0-6 months (n=24). They showed that there was significantly more frontal EEG power across all frequencies in 4-6 month olds across the phase of recovery from anesthesia compared 0-3 month olds, likely reflecting developmental differences. In addition, they found that the frontal alpha coherence, which is considered a marker of functional arousal in adults, was absent in all the infants. Understanding these differences is therefore critical for revealing the influence and effectiveness of different anesthetic drugs on the brain of very young infants and highlights the importance of interpreting the EEG according to the appropriate developmental context.
Moving towards more systematic understanding
The existing research looks at only a few of the very many features of the EEG that could be studied and only in small slivers across the developmental trajectory. The portable nature of EEG today makes it much easier than ever before to conduct studies within the population. It is now time for large scale longitudinal datasets that will allow us to understand the dynamical development of the brain and its variability across human populations.
