Abstract: A device and method for acquiring and processing a patient's brain electrical activity is provided. Noise contamination during acquisition and transmission of the brain electrical signals is reduced by providing differential amplifiers in the patient sensor in close proximity to the electrodes. A guarding technique is applied in the patient sensor to avoid inductive coupling of low frequency environmental noise. Radio-frequency (RF) filters and a Faraday cage assembly are also provided in the patient sensor to reduce electromagnetic interference. The brain electrical signals acquired by the electrodes are transmitted through shielded cables to a handheld base unit for signal processing.