Amplitude is a key characteristic of any waveform, representing the peak value or "height" of the waveform. In the context of brain activity, as measured by EEG (electroencephalography), amplitude reflects the strength or intensity of the electrical signals generated by the neurons in the brain. These electrical signals are the result of the flow of ions across neuron membranes, which creates small voltage changes that can be recorded on the scalp.

1. Amplitude in EEG

Definition: Amplitude represents the strength or intensity of the electrical signals recorded by EEG, measured in microvolts (µV). It corresponds to the height of the waveform.

Range: Normal brain activity has an amplitude range of 10-100 µV, with most signals falling between 10-50 µV.

Normal vs. Abnormal States: During normal brain activity, the amplitude tends to be moderate. During abnormal states, such as seizures, amplitude can increase significantly.

2. Amplitude vs. Frequency

There is typically an inverse relationship between frequency and amplitude in EEG:

  • High-frequency waves (e.g., beta waves during active thinking) tend to have lower amplitude.
  • Low-frequency waves (e.g., delta waves during deep sleep) tend to have higher amplitude.

3. Importance of Amplitude in Diagnosis

Seizures: High-amplitude bursts, known as epileptiform discharges, are often seen during seizures.

Brain Disorders: Abnormal amplitude can indicate neurological conditions such as brain injury, tumors, or neurodegenerative diseases. A significant decrease in amplitude might signal reduced brain function.

4. Amplitude vs. Sensitivity

Amplitude: This is the true strength of the brain's electrical signals.

Sensitivity: A technical setting on the EEG equipment that determines how the waveform is displayed. High sensitivity amplifies the signal for clearer display, but doesn't change the actual amplitude of the brain's electrical signals.

Example: A high sensitivity setting might make small fluctuations in amplitude appear more pronounced on the screen, even though the actual brain activity hasn't changed.

5. Summary

  • Amplitude indicates the strength of brain activity and helps in diagnosing neurological conditions.
  • Frequency and amplitude are inversely related.
  • Sensitivity influences how signals are displayed on the EEG equipment but doesn't affect the true amplitude of the brain's electrical activity.

Understanding both the true amplitude of brain waves and the sensitivity settings of the EEG is crucial for accurate interpretation, especially in the context of diagnosing conditions like epilepsy or neurodegenerative diseases.