It is widely accepted that sleep helps to form long-term memory. Now, scientists from the University of Tuebingen in Germany have proposed that deep sleep may strengthen not only psychological but also immunological memories.
In an article published in Trends in Neurosciences, the researchers suggest that slow-wave sleep (SWS), also known as deep sleep, may strengthen immunological memories of previously encountered pathogens, in a system that shares some features with psychological memory.
They explain that without memory, innate response patterns would be insufficient to enable an organism to survive in a changing environment, and they argue that this is true both for the mind and body.
In the formation of psychological memory, the central nervous system (CNS) mediates responses to psychological events and forms lasting neuronal memory representations of relevant features of the physical and social environment.
The immunological memory stores data about antigens
The same, they say, happens with the immune system. The system is able to form long-lasting memories, which store key features of antigens in the T- and B-cell systems, enabling a faster, more effective response when re-encountering the antigen. T and B cells are highly specialized cells that defend against disease. Antigens are proteins found on the surface of pathogens.
Just as SWS helps to strengthen psychological memories, turning fragile, short-term snippets into stable, long-term memories, so, the team suggests, the immune system also uses SWS in memory formation to extract and store necessary environmental information, enabling sustainable adaptive responses in the future.
The researchers believe they are the first to suggest that theories of sleep and memory could affect all the organs of the body.
Memory consists of three processes:
- Encoding, or uptake of information to be stored into a cellular representation
- Consolidation, where the newly encoded representation, initially fragile and prone to decay, is transformed into a more stable and longer-lasting representation
- Recall, where the stored memory is reactivated to enable the execution of an adaptive response in appropriate environmental contexts.
When the immune system meets a bacteria or virus, it encodes it, collecting enough information to create “memory T cells.” These memory T cells will help the system to recall the same bacteria or virus in future and to be better prepared to fight the attack. The researchers argue that consolidation of the information happens during SWS.
It is also proposed that T cells would collect “gist information” rather than detailed information about pathogens, so that they can recognize not only the exact virus or bacteria next time, but similar ones also.
Senior author Prof. Jan Born says that if the T cells did not store gist information, the immune system might ultimately focus on the “wrong part of a pathogen” after a virus mutates some parts of its protein.
Studies have shown that after a vaccination, there are long-term increases in memory T cells which are associated with SWS. This supports the view that SWS contributes to the formation of long-term memories of general information, leading to adaptive behavioral and immunological responses.
The researchers argue that the CNS and the immune system both follow the same principles in the formation of long-term memory, based on the same principles of consolidation. They also propose that while the two systems are different, they share some common mechanisms, and that the successful functioning of both is linked to SWS.
Prof. Born says:
“We consider our approach toward a unifying concept of biological long-term memory foundation, in which sleep plays a critical role, a new development in sleep research and memory research.”
He calls for future research to examine what information is selected during sleep for long-term storage and how this is achieved. He suggests it could be useful in developing vaccines against malaria, human immunodeficiency virus (HIV) and tuberculosis (TB).
Earlier this month, Medical News Today reported on research suggesting a link between thecommon cold and lack of sleep.
Written by Yvette Brazier