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

c3 左运动感知

c4右运动感知

f3运动计划

f4左上运动感知

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

 

high frequency

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

电极会被整体改变如果减去参考电极

 

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.

参考电极要放置于非活动区域, 左耳垂或者右耳垂,或者两者通用,如果只用一个耳垂参考,EEG信号比较真实,但是其中靠近耳垂的脑电信号会减小。

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.

如果两个同用,可以减小这种不对称,但是因为电流在颅内流通 歪曲了EEG,除了这样,低振幅会被观察到在temporal区域。

 

 

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.

另外的,全部做平均,这种可以避免不对称,但是有些情况可能观察到的频路不在其原来的位置。
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.

有时候叫做bipolar双极,脑电信号实在两个活动的电极的记录的,

 

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.

如果电极数大于32,最好用平均,

 

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.