14 DAY TRIAL // With every new study, psychologists and brain experts find that their level of knowledge of the human brain is actually a lot smaller than they used to believe. For instance, a new research shows that various stages of sleep are directly linked to the long-term memory embedding process. In other words, the quality of your sleep is directly connected with the way your brain will manage and store memories for prolonged periods of time. The new study appears in the February 26th issue of the journal Neuron, which is published by Cell Press.
Researchers evidence that sleep has two major components or stages, namely the slow wave sleep, or SWS, and the rapid eye movement (REM) sleep. One of the main things that differs one from the other is the level of neural activity in a part of the brain called the hippocampus, which is critical for memory formation.
Previous studies have emphasized the importance of this portion working together with the neocortex, which is the section of the organ where long-term memories are stored. If they work together flawlessly during sleep, then memories will be managed and stored without a glitch.
“Given the importance of synchrony and spike timing in synaptic plasticity, and given the putative role of sleep in learning and memory, a key question is whether consistent spike timing relationships exist across cortico-hippocampal circuits during sleep, and whether these differ in SWS versus REM sleep,” Dr. Athanassios G. Siapas, an expert at the California Institute of technology who is also the senior author of the new research, wonders.
The study was conducted on the brains of sleeping rats, which were surveyed, as far as neural activity goes, with sophisticated techniques. The scientists noticed that, during SWS, direct connections between the two portions of the brain existed, but they were non-linear and occurred in spikes, or “ripples.” This suggests that these phenomena are the basic units of the process. Oddly enough, during REM, these interactions greatly diminished. Instead, activity levels in the neocortex increased.
This can only mean that the SWS and REM deal with transfer and reorganization, respectively, and that the two processes rarely overlap. This may be a form of adaptation that the human brain has developed in order to ensure that memories are stacked neatly on top of each other and not mixed together.
“It's possible that the scarcity of coordinated cortico-hippocampal spiking during REM sleep may explain why the awake-like neural activity in the prefrontal cortex during REM does not interact strongly with the hippocampus and therefore why dreams are, on the whole, forgotten,” the lead author of the study, graduate student Casimir Wierzynski, concludes.