Where is the O1 lead located in relation to the T3 lead?

Where is the O1 lead located in relation to the T3 lead?

• A. Right and behind, 20% of the total circumference
• B. Left and behind, 25% of the total circumference
• C. Left and behind, 20% of the total circumference
• D. Right and behind, 25% of the total circumference

Answer: (C)

In the 10-20 EEG system, the letters indicate the region and the side, while the number helps place you on the left or right and along the anterior-posterior axis. O stands for occipital (the back of the head) and T stands for temporal (near the temples). O1 is on the left side of the occipital region, which is toward the back of the head. T3 sits on the left temporal region, which is more lateral and anterior to O1. So the relationship is that the O1 lead is left and behind (posterior to) the T3 lead. The 20% figure corresponds to the typical around-the-head spacing used in the 10-20 system, placing O1 about one-fifth of the head’s circumference away from the reference point toward the back.

In the 10-20 EEG system, the letters indicate the region and the side, while the number helps place you on the left or right and along the anterior-posterior axis. O stands for occipital (the back of the head) and T stands for temporal (near the temples). O1 is on the left side of the occipital region, which is toward the back of the head. T3 sits on the left temporal region, which is more lateral and anterior to O1. So the relationship is that the O1 lead is left and behind (posterior to) the T3 lead. The 20% figure corresponds to the typical around-the-head spacing used in the 10-20 system, placing O1 about one-fifth of the head’s circumference away from the reference point toward the back.