New research conducted by brain researcher Avi Karni of the University of Haifa in Israel

explores the possibility that naps help lock in sometimes fleeting long-term memories. A 90-minute daytime【C1】______. might help the most, the study finds.

"We still don't know the【C2】______mechanism of the memory process that occurs during sleep, but the【C3】______of this research suggest it is possible to【C4】______up memory consolidation," Karni said.

Long-term memory【C5】______to memories that stay with us for years, such as "what" memories -- a car accident that happened yesterday -- or " how to " memories, such as one's learned【C6】______to play the drums.

Karni, who【C7】______the study in a recent issue of the journal Nature Neuroscience,【C8】______participants to learn a complex thumb-tapping sequence, then【C9】______the study subjects into two groups: one that【C10】______for an hour, and one that didn't. The people who took an afternoon snooze showed【C11】______improvement in their performance by that evening.

"After a night's sleep the two groups were at the same【C12】______, but the group that slept in the afternoon【C13】______much faster than the group that stayed【C14】______," Karni said.

【C15】______, the study also showed just how much【C16】______a 90-minute nap could help lock in long-term memories.

"Daytime sleep can【C17】______the time 'how to' memory becomes【C18】______to interference and forgetting," Karnl said. "【C19】______of 6 to 8 hours, the brain【C20】______the memory during the 90-minute nap. "

【C1】

A．snack

B．nap

C．sleep

D．exercise