EEG reference is the basic of operation for signal analysis , since you would like to reduce the noise greatfully, the problem is that you have seen so many kinds of technology to do the rerefence such like average common(all channels mean) , earlobe(two linked or one ) mastoids, you will be get fucked for most of time about these if you don’t try them all,
based on the cow’s experiment we have a general idea about the rerefence,
for few channels you’d better not to use averge commer mean, not in a hurry let talk a little about the EEG
the above figure would show you the concept of recording the signal , how smart guy wonder to be lazy to do this , so the rerefence electricode is key for our later research,
FP1 前额attention fp2 判断力
The figure above shows the standard 10-20 system electrode placements and the basic brain functions that are located beneath each of the electrodes.
the speed of the brainwaves is measured by the numbers of per second of peak,and reflects the degree of activation of the area of the brain under the electrode. These types of brain electrical activity also reflect the level of arousal of the person
low frequency show that the low level blood (reduced perfusion) and fuel use (glucose uptake) in that part of the brain.
Delta (1-4 Hz),Delta activity accompanies deep sleep 1-4赫兹深度睡眠状态
Theta (4-8 Hz)Theta activity accompanies states of drowsiness and deep relaxation4-8赫兹 嗜睡
Alpha (8-12 Hz)Alpha is asociated with relaxed but awake states8-12赫兹 清醒放松
lower Beta (13-16) is associated with relaxed but attentive focus 13-16 专注力
middle Beta (15-20 Hz) with an engaged or active state of mind15-20 活动状态
higher Beta (>22 Hz) with an excited, hypervigilant, or urgent/emergency state of mind.紧急状态 兴奋
this electrode would be affected by global voltage changes in the same manner as all the other electrodes, such that brain unspecific activity is subtracted out by the referencing
The reference electrodes should be placed on a presumed “inactive” zone. Frequently, this is the left or right earlobe or both of them. If one earlobe electrode is used as a reference, the topography of EEG rhythms is rather close to true, but there is the systematic decrease of EEG amplitude in the electrodes which are closer to the reference side.
If “linked” earlobes are used, this kind of asymmetry is avoided but this distorts the EEG picture since the electric current flows inside the linking wire. This affects the intracranial currents that form the EEG potentials. Besides this, low-amplitude EEG is observed in both temporal areas.
Alternatively, the EEG may be recorded with any scalp electrode as a reference, and then the average reference is computed as a mean of all electrodes. It avoids all kind of asymmetry and makes the EEG recorded in various laboratories comparable. But in some cases using the common reference may reveal rhythms not at their actual location.
Sometimes the so called bipolar recording is used when the potential is measured between two active electrodes. This scheme is good for exact location of some locale potential changes, i.e., pathological activity focus.
With multi-channel recordings (e.g. >32 channels), it is common to compute the “average reference”, i.e. to subtract the average over all electrodes from each electrodes for each time point. This distributes the “responsibility” over all electrodes, rather than assigning it to only one of them.
It is difficult to find a reference electrode that captures only the noise that is contaminating your electrodes of interest without capturing brain activity in itself and without introducing new sources of artifact.