Psychological memory makes us. “If we couldn’t recall the who, what, where, and when of our everyday lives, we would never be able to manage. We mull over ideas in the present with our short-term memory, while we store past events and learned meanings in our long-term memory.”
Sleep — the natural and reversible state of reduced responsiveness to external stimuli and relative inactivity, accompanied by a loss of consciousness — supports the retention of memories of facts and events. Sleep in mammals consists of two core stages: slow-wave sleep, and rapid-eye-movement sleep, which alternate in a cyclic manner. Slow-wave sleep, often referred to as deep sleep, is important for transforming fragile, recently formed memories into stable, long-term memories.
In addition to psychological memory, there is another type of memory — immunological memory. Immunological memory is the ability of the immune system to respond more rapidly and effectively to a microbe that has been encountered previously. It is due to unique populations of immune system cells called memory B cells and memory T cells. An individual with a strong memory response to a specific microbe is said to be ‘immune’ to that microbe — this is because a strong memory response protects that individual from developing the disease caused by that microbe. Vaccines — modified forms of microbes — induce immunological memory and, by doing so, enable the immune system to respond more rapidly and effectively when encountering the original microbe.
Now, in an article published in the scientific journal Trends in Neurosciences, scientists propose that deep sleep may also strengthen immunological memories of microbes previously encountered because of either natural infection or vaccination. Indeed, in humans, long-term increases in memory T cells are associated with deep slow-wave sleep on the nights after vaccination.
Senior author Jan Born of the University of Tuebingen said in a press release: “While it has been known for a long time that sleep supports long-term memory formation in the psychological domain, the idea that long-term memory formation is a function of sleep effective in all organismic systems is in our view entirely new. We consider our approach toward a unifying concept of biological long-term memory formation, in which sleep plays a critical role, a new development in sleep research and memory research.”
The scientists propose that, although responding to different environmental events, the central nervous system and the immune system share basic functions of memory, and sleep leads to the consolidation of psychological and immunological memory. In both systems, the consolidation of memory is mediated by slow-wave sleep that suppresses certain signals while enhancing others.
In the same press release, Born added: “In order to design effective vaccines against HIV, malaria, and tuberculosis, which are based on immunological memory, the correct memory model must be available. It is our hope that by comparing the concepts of neuronal and immunological memory, a model of immunological memory can be developed which integrates the available experimental data and serves as a helpful basis for vaccine development.”