2.1 The neural origin of EEG

EEG originates from the synchronous synaptic activity of a large number of neurons in the cerebral cortex, and the main contribution comes from pyramidal cells.

Resting potential: Negative inside and positive outside, K+ inflow. Action potential: negative on the outside and positive on the inside, Na+ inflow.

Requirements for EEG generation: close proximity, large number, and good synchronization.

Scalp EEG versus direct cortical recordings: Amplitude differences.

volume conduction: There is a lot of depletion of electrical activity.
Space smearing effect: low spatial resolution (electrodes are placed on the scalp, the closer they are, the more similar they are, that is, the performance of low spatial resolution).

EEG measurements must be placed on the scalp. The essence of EEG is voltage, and the unit is uV.

During measurement, electrocardiogram, myoelectricity, oculoelectricity, and skin electricity also appear, all of which are regarded as noise .

EEG data must have reference electrodes, because the essence is voltage , and voltage is the difference between two points, so there must be reference electrodes.

The waveform of the reference electrode itself is a straight line that is always 0 (if there is only one; but if there are many, not necessarily, it should be averaged).

The deeper the electrode is inserted, the better the signal-to-noise ratio. The best signal-to-noise ratio is LFP. MUR mainly records action potentials.
LFP: Local Field Potential (Local Field Potential), refers to the weak potential changes measured in brain tissue or other biological tissues. LFP is often used to study the functions and activities of the nervous system, especially the information related to the collective activities of multiple neurons.
MUR: Multiple Unit Response refers to the activity of different types of neurons recorded in response to stimuli or tasks in electrophysiological experiments. Observing different types of unit responses provides insight into the diversity of how neurons are assembled and encoded.
MUA : Multi-Unit Activity (Multi-Unit Activity), usually refers to the activity of a large number of neurons recorded simultaneously in the nervous system. MUA is the integration of unit activity signals of multiple neurons to provide more comprehensive information to better understand the function of neural circuits and neural networks.

These can all be understood as brain electricity.

EEG: electroencephalogram.
ECoG: electrocorticogram. ECoG is also an invasive BCI technique that is being used. It measures the electrical activity of the brain from the surface of the brain. In this procedure, EcoG electrodes are implanted in the brain, where they sit on top of the cortex and measure potential changes in the surface of the cortex.

2.2 Measurement of EEG

EEG is the electrical signal (voltage) generated by the brain activity recorded on the surface of the scalp. It has the characteristics of fast change (ms), small amplitude (uV), and easy interference . The corresponding EEG recording equipment should have high sampling rate and signal Amplification, noise reduction and digitization features .
The essence of EEG recording equipment is a sensitive voltmeter with high time resolution . (personal opinion)