Modernization may have influenced the emergence of a strong alpha oscillation in the human EEG and contributed to greater diversity in brain dynamics.
Alpha: the archetypal cerebral rhythm?
If you look at an EEG trace from someone sitting quietly with their eyes closed then more often than not you will see a characteristic oscillating wave which represents “alpha” – one of the first characteristics of brain waves described by Hans Berger shortly after he performed the very first EEG recording in 1924.
Since then, alpha waves have been implicated in a wide variety of different cognitive and sensory processes, including attention, working memory and creativity as well in a range of clinical disorders (for example, see this review by Erol Basar).
But the widespread nature of alpha also makes it difficult to precisely pin down it’s fundamental role in the brain. One theory by Wolfgang Klimesch suggests that alpha activity is related to cortical inhibition during attention, whilst other researchers such as Matias and Satu Palva suggest that it is more complex than that.
Alpha. Fixed or flexible?
What is clear is that alpha is a fundamental rhythm in the brain across domains of attention, memory and consciousness. It is therefore of considerable interest to EEG researchers to explore how it is modulated by behavior and experience.
And although alpha is often considered to be the “dominant” frequency, it can also show variability in how it manifests itself in the brain, and has been found to differ between individuals. For example, see this paper by Haegens et al.
This suggests that the concept of a consistent alpha wave within a fixed 8-12 Hz frequency window, may no longer be a valid assumption. And furthermore, an individual’s life experience may actually be coded into the biological manifestation of this rhythm.
An exploration into human diversity
Building on their recent finding that neural complexity can be influenced by life experience, researchers Tara Thiagarajan and Dhanya Parameshwaran recently explored whether modern-day environmental enrichment also has an impact on the underlying alpha rhythm as part of the Human Diversity Project .
The study was carried out in the Tamil Nadu region of India, across 48 different locations, ranging from large metropolitan cities through to remote rural communities of only 300 people. In each location the researchers measured the pattern of resting brain activity whilst participants sat for 3 minutes with their eyes closed using the 14 channel Emotiv EPOC wireless EEG headset. The researchers also obtained a range of demographic metrics such as income, education and geofootprint, and took a record of fuel, electricity, mobile phone and internet usage.
By analyzing the alpha oscillatory EEG for each individual, in particular the peak frequency and alpha energy (a composite of the amplitude and fidelity of the oscillation), they were able to examine the true variability of alpha rhythms in the brain across a broad spectrum of life experiences.
And they found something quite surprising.
A dramatic level of variability
Namely that, in contrast to most other studies of resting alpha, an observable peak isn’t an absolute. In fact they found that 20% of individuals showed no evidence of alpha oscillations in any of the 14 channels recorded, potentially suggesting that the waveform is not sufficiently strongly developed in these people to enable it to be visible at the scalp electrodes.
Furthermore the concept of a “variable” alpha reached new levels, as shown by a dramatic variability in alpha energy across the volunteers studied – a 1000x range with no centralizing mean (panel C).
Modern Living Influences Alpha Oscillations.
To explore this further the researchers then looked at the demographic factors collected, and divided people up according to their level of “modernity”.
They found that the presence, peak and energy of the alpha oscillation were all closely associated with the access that people had to a modern lifestyle. More precisely, people classed as living a “modern” way of life, enjoying higher incomes and access to technology, demonstrated significantly more pronounced alpha oscillations compared to those who were classified as “transitioning” or “pre-modern” – many of whom displayed no evidence of an alpha peak within the analysis.
Although many demographic factors were positively correlated to an increased alpha energy and spatial prevalence, fuel consumption stood out as particularly interesting. Fuel consumption is a proxy for motor vehicle based travel, and therefore speed or rate at which they would have to process visual stimulus. Greater speed of sensory stimulus would require greater focus on relevant stimulus while inhibiting others. Combining this with previous results linking neural complexity and geofootprint, it suggests that the extent and speed of physical motion and exploration is potentially a secondary factor, which contributes to differences in brain diversity.
Could the differences be due to something else?
Of course, it is possible that other unforeseen factors may be confounding the results too – life aspects that were not recorded may be more direct drivers of the changes. However some possible alternative explanations could be eliminated by the control experiment that the researchers performed, where they recorded EEG from 20 people across 10 different sessions on different days. By looking at changes in alpha characteristics across the sessions, where there was no particular pattern, they were able to eliminate the suggestion that factors such as anxiety or unfamiliarity with EEG or technology were causing the largest differences observed.
New vistas for Alpha
By applying EEG in the real world, Sapiens Labs has been able to demonstrate how life experience plays a prominent role in the manifestation of resting alpha, and that the variability is much greater than previously recorded. An important consideration when thinking about the concept of a “normal EEG”, and further highlighting the rich diversity of the human brain across different walks of life.
These results point to the need for larger scale global datasets and differently designed experiments to understand this rhythm and its role in human brain function.