Frequency in EEG is influenced by:

The correct answer is related to how frequency in an EEG is fundamentally determined by the sampling rate of the data acquisition system, which is measured in hertz (Hz). In the context of EEG, frequency refers to the number of cycles of a waveform that occur in one second. The sampling rate dictates how often the EEG signal is sampled during data collection; a higher sampling rate captures more data points, allowing for a more accurate representation of the frequency content of brain waves.

When the sampling rate is too low, high-frequency components might be missed or misrepresented, leading to incorrect interpretations of the brain's electrical activity. Therefore, the relationship between sampling rate and frequency is critical in ensuring that the EEG accurately reflects the brain’s electrical patterns.

The other options, while they refer to important concepts in EEG, do not influence frequency in the same direct way. Sensitivity affects the amplitude of the signals, common-mode rejection ratio (CMRR) relates to noise reductions, and impedance involves the resistance to the flow of electrical current. None of these measures directly affect the frequency itself, making the choice regarding sampling rate the most relevant in determining frequency in EEG recordings.