my question is,a signal recorded at each electrode is an activity of the same brain area of the electrode placed or other areas of a brain activity will affect its recording ? if it so how can we analyze that signal, is there is any chance to study the different brain areas by constructing an algorithm based on measuring EEG signals ?
During EEG recordings, each electrode reads the signal from the head surface where its located (independently of the different montages and data analyses). Therefore, as it is a passive sensor, it should not imply changes in other head regions or electrodes. In this way, scalp recordings of neuronal activity in different brain regions allow the measurement of potential changes between the different electrodes over time with high temporal resolution; a multi-channel representation. I attach you a more illustrative specification.
http://www.edumed.org.br/cursos/neurociencia/MethodsEEGMeasurement.pdf
EEG activity is influenced by cortical brain activity near both the electrode of interest and the reference electrode because a recording requires current passing through both electrodes. Recordings may also be influenced by seemingly far away brain regions due to volume conduction. Although this is rare in simulation.
See the attached book chapter, section 4.
Chapter Electroencephalography (EEG): neurophysics, experimental met...
EEG is not brilliant for studying the cortical spatial information, but you can salvage some estimates if you have the correct data (e.g. high density EEG recordings, functional, and/or structural MRI, polhemus or other form of navigation software). EEGLab has some good tools for studying independent components, which can be further supported by source estimates, although this then has some complications at the group level due to individual differences across a number of factors generating the EEG signal.
http://sccn.ucsd.edu/wiki/Independent_Component_Clustering_Example
This tool is a nice starting place. If I remember rightly there is another technique called source projection, but I'm not overly familiar with this.
EEG signals are most commonly recorded using differential amplifiers utilizing 2 inputs and a reference. Recording signals are thus dependent on the electrode impedances, & the amplifiers characteristics (such as, input impedance, common mode rejection ratio etc.) as well as the many factors generating the signals. These factors can include many sources of undesirable far filed effects such as eye & tongue movements. Never-the-lass we can measure signal at a particular electrode and make reasonable statistical inferences on location of brain sources as well as how other brain areas affects the signal recording at this particular location. For example, quite good recordings can be made for early evoke potentials with reasonable statistical inferences on middle and later components.
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