What parameter is primarily used to evaluate brain electrical activity?

The primary parameter used to evaluate brain electrical activity is waveform frequency. This is because the electrical activities of the brain are represented as waves, which can vary in frequency. Different brain states, such as awake, drowsy, or asleep, are characterized by distinct frequency patterns. For instance, alpha waves are typically present during relaxed wakefulness, while delta waves dominate during deep sleep. Analyzing these frequencies through the EEG allows technologists to interpret the brain's electrical activity and identify potential abnormalities or conditions.

The other parameters, although relevant in the context of EEG, are not the primary focus for evaluating brain activity. Voltage refers to the strength of the electrical signal but does not provide insight into the state or function of brain activity on its own. Current, which is the flow of electrical charge, is more relevant in circuit theory. Impedance, on the other hand, is a measurement related to the resistance of the electrode-skin interface and is important for ensuring good signal quality, but it does not directly measure brain electrical activity.