Slow sampling rate may cause fast frequencies to appear slower due to what phenomenon?

The correct answer is related to the phenomenon known as aliasing. When the sampling rate of an EEG recording is too low, it cannot accurately capture the rapid changes in the electrical activity of the brain. This limitation leads to a misrepresentation of the frequencies present in the signal. Specifically, fast frequencies may be sampled in such a way that they appear to be much slower than they actually are.

Aliasing occurs because, according to the Nyquist theorem, a signal must be sampled at least twice the highest frequency present in order to be accurately reconstructed. If the sampling rate is insufficient, higher frequency components can be misrepresented as lower frequencies, resulting in an inaccurate depiction of brain activity in the recorded EEG.

For instance, if the actual frequency of brain waves is higher than half the sampling rate, it can fold back into the lower frequency range, leading to confusion in interpreting the EEG. Thus, aliased signals can significantly affect the analysis and diagnosis of neurological conditions, emphasizing the importance of using a sufficiently high sampling rate to preserve the integrity of fast-frequency brain activity.