Which electrode site is located half the distance from O2 to C4?

The correct answer is P4 because it is located at the specified distance from the O2 and C4 electrode sites on the scalp. In a standard 10-20 EEG electrode placement system, the locations of the electrodes are defined by specific measurements from reference points on the head.

The O2 electrode is positioned over the right occipital lobe, while C4 is located over the right central area. The P4 electrode is placed in the parietal region and lies between the two specified points, being equidistant from both O2 and C4. This placement is essential for capturing brain activity in the parietal region, which may be relevant for understanding sleep patterns.

Other choices present valid electrode sites, but they do not meet the requirement of being positioned exactly halfway between O2 and C4. T6, for example, is located at the temporal area which is not aligned with the necessary spatial relationship to the other two points. Similarly, T4 is also in the temporal region rather than the parietal section needed for this question. P6 is located further out towards the side of the head than P4, thus not fulfilling the distance criteria between O2 and C4. Thus, P4 is the correct