EEG (electroencephalography) readings provide crucial information about the electrical activity in the brain. The speed at which these tracings are displayed, referred to as the reading speed, can significantly affect how the data is perceived and interpreted.

1. What is EEG Reading Speed?

Reading speed refers to how fast the EEG tracings are presented on the screen or paper, typically measured in millimeters per second (mm/sec). The higher the reading speed, the fewer seconds of data are shown on the screen at any given moment. Conversely, a slower reading speed shows more data over the same period.

2. Typical Reading Speeds:

  • Adult Standard Speed: 30 mm/sec
  • Neonatal Standard Speed: 15 mm/sec

These speeds are chosen based on the expected duration of the brain waves being observed and the desired level of detail.

3. How Reading Speed Affects Data Presentation:

Higher Reading Speed (e.g., 60 mm/sec):

  • The data appears more stretched out.
  • The tracings are less detailed, as the waveforms are spread over a larger area.
  • This can make the waves lose their characteristic morphology (shape).

Lower Reading Speed (e.g., 15 mm/sec):

  • The waves appear condensed, with more data shown in a smaller space.
  • This can cause the tracings to appear sharper and more compressed, which might make normal waves look like abnormal, epileptiform spikes.

Standard Reading Speed (30 mm/sec):

  • This speed is considered optimal for most adult EEGs, balancing detail and clarity.
  • The waveforms appear neither too stretched nor too compressed, providing an accurate representation of brain activity.

4. Historical Context:

EEG tracings were historically recorded on scrolling paper. The speed at which the paper moved determined how quickly the traces were drawn.

  • Paper Speed: When the paper moves at a higher speed, the waves appear stretched out, and when it moves slower, the waves are compressed.

5. Why Reading Speed Matters:

Interpretation: Choosing the appropriate reading speed is crucial for accurate interpretation. A speed that is too high can cause important waveforms to lose their details, while a speed that is too low can make normal patterns appear abnormal.

Diagnosis: Properly adjusted reading speed ensures that brain waves, such as alpha, beta, theta, and delta waves, are displayed accurately, helping clinicians make better-informed decisions regarding brain activity, such as identifying seizures, sleep disorders, or neurological abnormalities.

Conclusion

Understanding EEG reading speeds is vital for ensuring that brain activity is represented accurately. The ideal reading speed strikes a balance between too stretched and too condensed waveforms, with 30 mm/sec being the most commonly used speed for adults.