Harry was always one to accept a dare, and this dare seemed like fun. All he had to do was put on a pair of roller skates and skate backward for 100 feet. Harry had not been on skates since he was ten but was confident that he could remember. He put on the skates, stood up, and started forward. He was moving forward okay but now came the hard part- turning 180 degrees and skating backward. He tried to twist his body and turn his feet but everything got tangled up and he fell over backwards with his head hitting the concrete with a loud thud. When Harry slowly sat up, he rubbed his head and wondered why he was seeing stars. Which part of Harry's brain was hurt when he hit the concrete?