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)