Electroencephalogram (EEG) recordings measure electrical activity in the brain that is the result of electrochemical signaling between neurons.

These electrochemical signals travel through the brain and skull, and can be recorded by electrodes applied directly to the scalp. In a typical set-up, researchers will make EEG recordings using an electrode cap that is placed on the head, which consists of 32, 64, 128 or 256 electrodes. Beneath each electrode are many thousands of neurons. Slight changes of voltage in the axons of these neurons are called graded potentials. Each electrode records the sum of the graded potentials of the many thousand underlying neurons. EEG is a particularly valuable tool to neuroscientists, because it is sensitive to millisecond changes in neural processing. This property, known as temporal resolution, is far superior to that of functional Magnetic Resonance Imagery (fMRI) or Positron Emission Tomography (PET). However, a major drawback with EEG is its’ poor spatial resolution, meaning it is relatively ineffective at differentiating specific regions or circuits in the brain, i.e. it does not give a very good image of neural processes at work.

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