EEG Amplification

EEG amplification, also known as gain or sensitivity, plays a crucial role in EEG recordings by determining the magnitude of electrical signals detected by the electrodes placed on the scalp. Here is a detailed explanation of EEG amplification:

1.Amplification Settings: EEG machines allow for adjustment of the amplification settings, typically measured in microvolts per millimeter (μV/mm). Common sensitivity settings range from 5 to 10 μV/mm, but a wider range of settings may be used depending on the specific requirements of the EEG recording.

2.High-Amplitude Activity: When high-amplitude signals are present in the EEG, such as during epileptiform discharges or artifacts, it may be necessary to compress the vertical display to visualize the full range of each channel within the available space. This compression helps prevent saturation of the signal and ensures that all amplitude levels are visible.

3.Vertical Compression: Increasing the sensitivity value (e.g., from 10 μV/mm to 20 μV/mm) results in vertical compression, where the output amplitude is compressed into a smaller space. This is useful for highlighting high-amplitude activity but may reduce the visibility of low-amplitude signals.

4.Low-Amplitude Activity: Conversely, low-amplitude signals, such as background EEG activity, require lower sensitivity values to increase the visibility of subtle changes. However, setting sensitivity values below 2 μV/mm for cerebral activity may not be practical due to noise levels.

5.Frequency Filtering: EEG devices typically record activity within a frequency range of 0.1 to 125 Hz. Standard review settings often use a narrower bandpass with a low-frequency filter (LFF) of 1 Hz and a high-frequency filter (HFF) of 70 Hz. These filters help isolate EEG activity within the clinically relevant frequency range.

6.Notch Filter: In addition to the bandpass filters, EEG machines may include a notch filter set to the frequency of the power supply's AC current. This filter helps reduce noise from environmental electrical currents, creating a cleaner EEG signal for analysis.

7.Impact on Interpretation: Proper amplification settings are essential for accurate interpretation of EEG data. Inadequate amplification may lead to signal distortion or loss of important information, while excessive amplification can result in saturation and masking of subtle abnormalities.

By understanding and adjusting the amplification settings appropriately, EEG technicians and clinicians can optimize the quality of EEG recordings, enhance the visibility of relevant brain activity, and improve the accuracy of EEG interpretation.

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