From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
The Splitting Headache (分裂 頭痛, Bunretsu Zutsū) is an energy beam attack used by Gotenks in his Super Saiyan 3 form. First, Super Saiyan 3 Gotenks raises his hand up in the air and forms a huge golden-yellow energy sphere. Next, he fires the sphere into the air and it fires down on his opponent, splitting them in half. Finally, Super Saiyan 3 Gotenks uses the Finish Flash to destroy the opponent's two halves, inflicting a huge amount of damage.
 Dragon Ball Z
Super Saiyan 3 Gotenks used this attack in his battle against Super Boo. After being thrown into a lake by Super Boo, Super Saiyan 3 Gotenks rose up into the air behind Super Boo and attacked him with the Splitting Headache, blasting the Majin into two parts. He then used the Finish Flash and blasted Super Boo into pieces. The surrounding pieces joined together to reform Super Boo, however, allowing him to squeeze Gotenks and send him crashing into a mountain.
 Data guides
Splitting Headache is named Burēn Kurasshu Hanmā (ブレーン クラッシュ ハンマー, Burēn Kurasshu Hanmā; Literally meaning "Brain Crash Hammer") in Daizenshū 7.