“Have some almonds to sharpen your memory” or “Play these brain games to improve your memory” are some phrases we’ve often heard. Now, what if I tell you that improving your memory could be as easy as sleeping? And, no, I don’t mean that figuratively. Sleep is instrumental in the transfer and consolidation of memories in the cortex.
Our health, vitality and mental faculties are extremely dependent on sleep, so it comes as no surprise that sleep influences memory and plasticity too. Scientists began to research sleep patterns in the 18th century. In 1729, Jean Jacques d’Ortuous de Marian researched the circadian rhythms of plants, rousing interest in human sleep. The interrelationship between sleep and memory has been studied as early as the 19th Century. In 1801, British psychologist David Hartley inferred that during the rapid eye movement (REM) periods of sleep, dreaming modified the associative memory links within the brain. The first systematic studies on sleep and memory conducted in 1924 by Jenkins & Dallenbach showed that retention was better after a night of sleep than that following a night of staying awake. In the consequent years, optimal sleep and its mentally restorative effects became rich subjects for scientists to mine. Memory is essentially a cognitive process that enables the encoding, storage and retrieval of information. Memory storage is like an elaborate and sophisticated filtration process.
Usually, external stimuli are encoded in our brain within milliseconds. The brief sensory memory is responsible for registering a visual pattern, a sound or a touch. It is then stored in short-term memory, which has a sparse capacity. Try remembering a ten-digit number without repeating it to yourself. Practice, studying, and use of the information transfer it to long-term memory. Long-term retention of memory can take hours, days or even years. Unlike the ephemeral quality of sensory and short-term memory, long-term memory has a huge capacity to retain information indefinitely. The initial formulation of the memory is a rapid process, but it continues to evolve and sleep acts as an able accomplice in its adaptation.
The memory process is essentially divided into three stages. The first is called Acquisition and refers to the introduction of information into the brain. The second stage is called Consolidation, which involves the processes wherein the memory becomes stable. The final stage is called Recollection and refers to the ability to recall or access the once acquired information. Sleep is essential for the second and third stages. Sleep helps learning and memory in two ways. Firstly, a sleep-deprived person will not be able to focus their attention or concentrate optimally, thus, impeding their mental skills. Secondly, sleep itself plays an important role in the Consolidation and Recollection stages. Memory consolidation happens while we’re asleep by strengthening our neural connections, which formulate memory.
Our sleep is divided into five sleep cycles, the first four collectively referred to as non-rapid eye movement (NREM), which involves switching from wakefulness to sleep, light sleep, and then deep sleep. The last cycle is the rapid eye movement (REM) period, which begins after a deep sleep and is also the stage wherein dreams occurs right before wakefulness in the morning. This cycle takes 90–110 minutes to complete, and research suggests that procedural and declarative memory consolidation usually happens in this stage, preparing our brain to learn new information the following day. Procedural memory is a type of instructional, long-term memory involving how to perform different actions and skills. Declarative memory is a type of long-term memory requiring conscious recollection and includes memory for facts and events.
Not sleeping or getting enough sleep can lower our learning capacity by as much as 40%. During the NREM period, the brain also sorts through our various memories from the previous day, filtering and saving the memories it deems important and banishing the other information to the subconscious realm of our brains. The selected essential memories become more concrete during deep NREM sleep and are further consolidated (made to stick) during the subsequent REM sleep. A growing body of research suggests that emotional memories can be strengthened in the REM stage of sleep.
There is a general agreement between scientists today that memory consolidation occurs in both the REM and Non-REM phases of sleep.
Sleep Deprivation and Brain Function
People who don’t get the required amount and quality of sleep, which is 6-8 hours for adults, suffer from sleep deprivation, difficulty remembering things as the first indicator. When we don’t sleep well, our brain does not have enough time to establish new pathways for consolidation of the information that we have recently acquired, affecting our short term memory directly, and impeding the formation of long term memory. Other cognitive effects of insufficient sleep include impaired focus and learning, poor behavioural and emotional control, and faulty decision-making skills. Matthew Walker, scientist and professor of neuroscience and psychology at the University of California, Berkeley, writes in his bestseller, Why We Sleep, ‘…if you don’t sleep the very first night after learning, you lose the chance to consolidate those memories, even if you get lots of “catch-up” sleep thereafter. In terms of memory, sleep is not like the bank. You cannot accumulate debt and hope to pay it off at a later point in time. Sleep for memory consolidation is an all-or-nothing event.”
Interconnection Between Dreams And Memory
Our most vivid and interesting dreams usually occur during REM sleep when our eyes move rapidly, but our bodies are still. During REM sleep, our newly consolidated memories get interconnected with our prior memories, including our daily lives and other trivia or facts that we may know of. This connection is sometimes the reason why people find inspiration or conjure new ideas or solutions while dreaming! Some of the ideas and inventions which were literally dreamt of include the Periodic Table, the DNA’s Helix Structure, Einstein’s Theory of Relativity, Salvador Dali’s Persistence of Memory, etc. (Take from EMDR book)
Nothing can better equip us for the next day than a full night’s rest. Good sleep aids in the consolidation of memories. Filmmaker Akira Kurosawa’s words ring true – ‘Man is a genius when he’s dreaming.’