Researchers have known for some time sleep is important for memory formation. This is especially true for procedural memory, the kind that applies to the brain retaining newly learned, how-to tasks, such as riding a bicycle.
The processes that occur during sleep and help consolidate memory, however, remain something of a mystery. Stuart Fogel is working to uncover parts of that mystery.
“Sleep is really important when we learn something new; that memory is very fragile and it can be easily forgotten or replaced by something else. Sleep is important in solidifying that,” said Fogel, an adjunct professor in Psychology at Western and professor at University of Ottawa’s Sleep Research Laboratory.
“We want to know what’s happening during sleep. We know sleep is important for memory transformation to occur and for the subsequent improvement and performance. But what we don’t know is exactly what is happening, what mechanisms are involved.”
In partnership with colleagues at the universities of Ottawa, Montreal and Western, Fogel recently co-authored a study indicating sleep is not only important in solidifying procedural memory, but also strengthens the putamen, the brain’s reward structure, leading to better memory consolidation.
“We are mainly interested in the role sleep plays in consolidating, solidifying or enhancing memory after we learn something new during the day. In order to do that, we leveraged technology that’s been around for some time, but advancements now allow us to apply this to study sleep,” Fogel said.
His research team combined the use of EEG, which measures brain waves from the scalp, and MRI, which allows researchers to take functional pictures of brain activation, using the two simultaneously during a study participant’s sleep after performing procedural tasks.
“We combined these two things and that enabled us to take the information we know about sleep and apply it to brain imaging. That becomes a powerful combination that enables us to find exactly the role sleep plays in memory processing, what’s happening during sleep while these memories are being processed, and we can compare it to what happens while awake,” he explained.
“While (performing a task), the brain is sending you reward signals that you’re doing things correctly. We saw this pretty predictable and well-known pattern of brain activation while you’re learning and we wanted to see what happens afterwards, when you go to sleep. So, we had people actually sleep in the scanner with the EEG recording as well,” Fogel continued.
“What we saw there was gradually, over the course of sleep, this memory trace was transformed from this cortically dominant trace to a more subcortically dominant trace. The memory was transformed so this brain structure, the putamen, was strengthened as a result of this sleep period that occurred after the learning episode.”
The important finding here is the communication that occurs in the brain’s network while the individual is asleep, he explained. The better the communication between the putamen and the cortical structures of the brain – something improved during sleep – the better the performance and memory consolidation process appears to be.
“This transformation of the memory trace only happened during sleep and not during the intervening periods of wakefulness that occurred. So, it seems to be a very sleep-specific process that unfolds,” Fogel said.
He continues to investigate these processes, looking at bursts of brain activity, called spindles, that occur during light sleep.
“What might be happening is the memory traces might be reactivated and this repeated reactivation is strengthening subcortical memory traces while were sleeping,” he noted.
“What is it about sleep that is so important? What types of memory might this apply to and how does this process change as the lifespan unfolds? As we get older, and sleep changes and memory changes, what are the implications? We want to know if this type of process is impacted by aging.”
This study spanned much of Fogel’s career, starting with Julien Doyon as a postdoctoral scholar in Montreal, continuing at Western while he worked with Psychology professor and Brain and Mind Institute member Adrian Owen, and leading to present day in his research undertakings in Ottawa.