Sleep plays an important role in the brain's ability to consolidate learning when two new potentially competing tasks are learned in the same day, research at the University of Chicago demonstrates.
Other studies have shown that sleep consolidates learning for a new task. The new study, which measured starlings' ability to recognize new songs, shows that learning a second task can undermine the performance of a previously learned task. But this study is the first to show that a good night's sleep helps the brain retain both new memories.
Starlings provide an excellent model for studying memory because of fundamental biological similarities between avian and mammalian brains, scholars wrote in the paper, "Sleep Consolidation of Interfering Auditory Memories in Starlings," published in the current online edition of Psychological Science.
"These observations demonstrate that sleep consolidation enhances retention of interfering experiences, facilitating daytime learning and the subsequent formation of stable memories," the authors wrote.
The paper was written by Timothy Brawn, a graduate researcher in psychology at UChicago; Howard Nusbaum, professor of psychology; and Daniel Margoliash, professor of psychology, organismal biology and anatomy. Nusbaum is a leading expert on learning, and Margoliash is a pioneer in the research of brain function and its development in birds.
For the study, the researchers conducted two experiments using 24 starlings each. They played two recorded songs from other starlings and tested the birds' ability to recognize and repeat the two songs. After learning to recognize the two songs, the birds were later trained to recognize and perform a different pair of songs.
In their experiments, the authors examined the effect of sleep on the consolidation of starlings' memories. After learning the second pair of songs, they were tested on the first before they went to sleep. They varied the time between testing.
Researchers found that learning the second pair of songs interfered with the birds' ability to remember the first pair, regardless of the time between the daytime testing periods. Learning the first pair of songs also interfered with the birds' ability to remember the second pair when they were tested on the second pair before they went to sleep.
When the starlings were allowed to sleep, however, they showed increases in performance on both the first and second pair of songs, suggesting that sleep consolidation enhances their memory, overcoming the effects of interference. When taught a new song pair after awaking, the birds were still able to remember what they had learned on the previous day, despite the new interference.
"The study demonstrates that sleep restores performance and makes learning robust against interference encountered after sleep. This process is critical to the formation and stability of long-term memories," Nusbaum said.