Forgetfulness May Depend On The Time Of Day

When you forget something, it may be because you did not truly learn it, such as the name of a person you were just introduced to, or it could be because you’re not able to recall the information from where it has been stored in the brain such as lyrics to your favorite song slipping your mind. 

How new memories are made is being studied by memory researchers, and the biology of forgetting appears to be more complicated to study than was anticipated because of the difficulties in distinguishing between not knowing something and not being able to recall a memory.

"We designed a memory test that can differentiate between not learning versus knowing but not being able to remember," said Kida.

Young adult mice had their memories tested in the learning/training phase of memory tests in which the animals were allowed to explore a new object for a few minutes. Later in recall testing the team observed how long the animals touched the object when it was reintroduced, the animals appeared to spend less time touching objects they remember seeing previously. Recall was tested by reintroducing the same object at different times during the day.

These experiments were carried out using healthy mice and those without the protein BMAL1 which regulates the expression of many genes and fluctuates between low levels being just before waking up to the highest levels just before going to sleep. 

Animals trained just before they would normally wake up that were then tested before they normally went to sleep recognized the object; those trained at the same time but tested 24 hours later didn’t recognize the object. Healthy mice as well as those without BMAL1 had the same results with those without the protein being even more forgetful before they normally woke up and the results were the same in these mice when tested for recognizing an object or another mouse. 

According to the researchers there is something about the time of day just before the animals normally wake up when these BMAL1 protein levels are normally low that causes the mice not to recall something they had learned and knew. They suspect that the circadian clock which is responsible for regulating sleep/wake cycles also affects learning and memory formation, but the purpose of having memory recall fluctuating depending on time of day remains unknown.

"Now we have evidence that the circadian clocks are regulating memory recall," said Kida. “If we can identify ways to boost memory retrieval through this BMAL1 pathway, then we can think about applications to human diseases of memory deficit, like dementia and Alzheimer's disease. We really want to know what is the evolutionary benefit of having naturally impaired memory recall at certain times of day," Kida explains.