The renaissance of the EEG
EEG or the Electroencephalogram in humans was discovered almost 90 years ago now by Hans Berger. The EEG is a bioelectric potential that is recorded from the surface of the head using appropriate electrodes and instrumentation.
Measurable EEG signals are very small (perhaps microvolt levels) and only occur when a population of cortical cells are excited in unison producing a group potential which is the sum of many small electrical potentials. Inspecting the recorded raw EEG signal back in 1929 we would have probably seen this recorded on a chart showing a complex, varying-amplitude, continuous-time signal. It's literally indescribable using words.
Interest in the EEG has both receded and grown over the years. The nature of the signals has provided a technical and analytical challenge but EEG is without doubt an area of growing interest now for a few reasons.
- the necessary technology available has become more affordable and certainly trivial compared with the cost of MRI or PET scanners
- new methods of EEG analysis are emerging facilitated by advanced software, hardware and analysis methods
- our understanding of the mechanisms and understanding EEG signals has grown
- the spatial resolution of EEG signals is high compared with other neuroimaging techniques
Today we can use Spectral Analysis and high speed processing rather than "the eye" of a trained observer to examine these signals as if we were to split them into their individual “frequency components”. This allows us to take advantage of our modern hardware and software to gain new insights into the patterns of change implicit within the EEG and start to quantify EEG.
qEEG stands for quantified EEG. By quantifying EEG activity in different brain areas, the activity in these areas and their interaction can be shown, both numerically but also by taking advantage of computer graphics to visualise the data with colour coded maps. Humans are great at recognising patterns and this is naturally appealing and practical.
The raw EEG and qEEG information derived from it can be therefore more easily interpreted and used as a clinical tool to evaluate brain function, and to track the changes in brain function due to various interventions such as neurofeedback training or medication.
qEEG data can also be compared to different qEEG databases such as the Neuroguide and used as an assessment and prognostic tool.
For neurofeedback training, typically only one or two channels of EEG are used. Electrodes are placed on positions defined in the so called International 10-20 EEG system so that recordings can be made on a consistent basis.
Often, clinicians who have learned to work with EEG will examine multiple points on the scalp simultaneously. The 10-20 system is an approach that identifies specific locations on the head from which EEG measurements are taken. This system identifies locations used to place the electrodes. These locations can then be identified for example as a letter and a number such as C3, CZ, C4 and so on.
The 10-20 system defines the exact location of 19 EEG channels plus the earlobes or mastoids. The locations are defined by taking distances of 10% and 20% of the total distance of the front to back of the head and between the two mastoids. This method was developed to ensure reproducibility so the clients could be compared to each other I'm themselves overtime. The system is based on the relationship between the location of an electrode and the underlying area the cerebral cortex.
One of the simplest forms of qEEG is a frequency spectral analysis. Most often qEEG is a general term that refers to a recording and quantification from the positions on the head often through special EEG Caps.
This analysis can provide an overview of the dynamic changes taking place throughout the brain during cognitive processing tasks and this novel approach can be used to assist us in determining which areas of the brain are engaging and processing efficiently or not. The techniques of qEEG can be used to identify mild traumatic brain injury when other techniques are unable to identify changes.
To get a full physiological view and improved insights into how the mind and body interact, true power lies in combining qEEG with other physiological signals like Heart Rate Variability (HRV), skin temperature, respiration rate and skin conductance (SC/GSR).