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.