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0.1. What Are Physiological Signals?

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Table of Contents

Physiological signals are electrical potentials generated as a result of the activity of living tissues. This application analyzes three main types of signals:

0.1.1. EEG (Electroencephalogram) #

Physiological basis: EEG records the electrical activity of the cerebral cortex. This activity arises from synchronized changes in the membrane potentials of large groups of neurons (pyramidal cells).

    How it works:

    • Neurons generate electrical potentials when transmitting information.
    • When thousands of neurons become active synchronously, their potentials sum together.
    • Electrodes on the surface of the head record these summed potentials.
    • The signal amplitude is typically 10–100 microvolts (µV).

    What EEG shows:

    • General brain state (wakefulness, sleep, coma)
    • Cognitive processes (attention, memory, thinking)
    • Emotional states
    • Pathological changes (epilepsy, tumors)

    EEG frequency ranges (and their physiological meaning):

    • Delta (0.5–4 Hz): Deep sleep, pathological conditions, infancy
    • Theta (4–8 Hz): Light sleep, meditation, creative thinking, learning
    • Alpha (8–13 Hz): Relaxed wakefulness with eyes closed, calm state
    • Beta (13–30 Hz): Active thinking, concentration, problem solving
    • Gamma (30–100 Hz): High-level cognitive processing, binding information from different brain areas

    0.1.2. ECG (Electrocardiogram) #

    Physiological basis: ECG records the electrical activity of the heart. Each heartbeat (systole) is initiated by an electrical impulse that propagates through the heart’s conduction system.

    How it works:

    • The sinoatrial node (the pacemaker) generates an electrical impulse.
    • The impulse spreads through the atria to the atrioventricular node and then to the ventricles.
    • Electrodes on the body record these electrical changes.
    • The R-peak in the ECG corresponds to ventricular depolarization (contraction).

    What ECG shows:

    • Heart rate (pulse)
    • Rhythm regularity
    • The state of the cardiac conduction system
    • Heart rate variability (HRV), an indicator of autonomic regulation

    Heart rate variability (HRV):

    • A healthy heart does not beat like a metronome—intervals between beats constantly change.
    • This variability is controlled by the autonomic nervous system.
    • High variability = good adaptability and health.
    • Low variability = stress, fatigue, and possible health problems.

    0.1.3. EMG (Electromyogram) #

    Physiological basis: EMG records the electrical activity of muscles. When a muscle contracts, muscle fibers generate electrical potentials.

    How it works:

    • Motor neurons send signals to muscle fibers.
    • Muscle fibers depolarize and contract.
    • Electrodes on the skin record this activity.
    • In this application, EMG is recorded from facial muscles (Zygoma — cheek muscles).

    What EMG shows:

    • Muscle tension
    • Facial reactions (smile, grimace)
    • Stress and emotional reactions (facial muscle tension)