#018 - Sleep spindles and memory consolidation for language acquisition.

#018 - In this episode Gabi will briefly point out at the main reasons in detail of why sleep is crucial for language learning and cognition in general.

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Transcript

Hi everyone my name is Gabi and today I’d like to talk about the relationship between sleep and second language acquisition.

Yeah, that’s right. There is a pretty straight-forward relationship between sleep and the consolidation of learning new languages. Who would’ve thought. 

In this episode you will learn why and how sleep in crucial to learn a new language and hopefully you will be able to implement a sleeping routine that helps you improve your memory, because as we will see, memory is key to learn new things.

Recent studies suggest that During sleep, the brain follows a process where it replays experiences we have had throughout the day so as to store them better in our memories.

Research into sleep learning has been debated for many years, yet current studies suggest that having a restful night’s sleep is an essential component of consolidating memories related to language study. It can’t be emphasized enough how vital it is to have adequate sleep in order to stay focused and energetic while forming new habits or making decisions. Being well-rested impacts mood favorably as well as it improves our general cognition.

The ability to acquire a second language depends on memory systems adapted to support language learning. Sleep plays an important role in the formation of newly acquired memory for both declarative memory and procedural memory.

But what is declarative and what is procedural memory?

Declarative or also called explicit memory is devoted to the processing of names, dates, places, facts, events, and so forth. These are entities that are thought of as being encoded symbolically and thus can be described with language. In terms of function, declarative memory is specialized for fast processing and learning.

Procedural memory

Procedural memory refers to cognitive and sensorimotor habits and skills learned through repetition. The repetition of an activity leads to the progressive consolidation of the memory trace of the involved skills, leading to their automation. It is involved in daily activities such as learning to tie shoes, ride a bike, or drive a car. 

Sleep happens in five stages: wake, N1, N2, N3, and REM. Stages N1 N2 and N3 are considered non-rapid eye movement (NREM) sleep, with each stage a progressively deeper sleep. A typical night's sleep consists of 4 to 5 sleep cycles, where a complete sleep cycle takes roughly 90 minutes.

1. The first stage is the wake stage or stage W, which further depends on whether the eyes are open or closed. During eye-open wakefulness, beta waves predominate. 

2. This is the lightest stage of sleep. This stage lasts around 1 to 5 minutes, consisting of 5% of total sleep time.

3. This stage represents deeper sleep as your heart rate and body temperate drop. It is characterized by the presence of sleep spindles This stage lasts around 25 minutes in the first cycle and lengthens with each successive cycle, eventually consisting of about 45% of total sleep

4. N3 is also known as slow-wave sleep (SWS). This stage is the most difficult to awaken from, and, for some people, even loud noises (> 100 decibels) will not awaken them. This is the stage when the body repairs and regrows tissues, builds bone and muscle and strengthens the immune system. This is also the stage when sleepwalking, night terrors, and bedwetting occurs.

5. REM or rapid eye movement is associated with dreaming and is not considered a restful sleep stage. This stage usually starts 90 minutes after you fall asleep, with each of your REM cycles getting longer throughout the night. The first period typically lasts 10 minutes, with the final one lasting up to an hour. REM is when dreaming, nightmares, and penile/clitoral tumescence occur.  

Rapid eye movement (REM) sleep is the stage of sleep where most dreams happen. During REM sleep, your brain activity looks very similar to brain activity while you're awake. REM sleep makes up about 25% of your total time asleep.

Non-Rapid Eye Movement (NREM) sleep, that is N1, N2 AND N3, is involved in declarative memory consolidation, where sleep spindles, which are basically a pattern of brain waves people experience during certain stages of sleep, serve as an important marker of consolidation. 

changes in spindle characteristics have been identified in response to both declarative, cognitively complex procedural memory consolidation as well as procedural skills memory.

A potential marker of this learning effect may be theta activity. A wealth of literature has shown that hippocampal theta activity is involved in processes that support the encoding of memories, and in particular, long-term potentiation. Long-term potentiation, or LTP, is a process by which synaptic connections between neurons become stronger with frequent activation. LTP is thought to be a way in which the brain changes in response to experience, and thus may be an mechanism underlying learning and memory

Likewise, sleep supports acquiring a new language through a different channel called offline memory processing.

Offline memory reprocessing has been used to refer to the process during which the brain cuts out normal input from the outside world, and looks for older memories that are relevant to memories from the recent past to see if the older memories can be usefully linked to the newer ones.

Studies have demonstrated that sleep enhances SLL in naturalistic settings, as a whole,as well as specific aspects of language learning including assigning meaning to words, enhancing phonological speech production, speech perception, integrating words into the mental lexicon, and learning implicit grammar.

What are naturalistic settings?

Naturalistic observation involves observing people in natural environments, like their home, work or a place that they enjoy visiting, to understand their normal routines and behaviors, and to avoid anxious feelings that may happen in a clinical setting.

In conclusion we could say two things:

The first thing is that:

NREM sleep has been found to support basic features of language learning such as speech perception.  NREM sleep is implicated in aspects of language learning that contain a declarative component, such as assigning meaning to words36 and integrating words into the mental lexicon. REM sleep is important for procedural memory consolidation of rules and strategies: abilities that are important for language processes such as grammatical skills.

The second thing is that:

Sleep spindles may contribute to declarative memory consolidation for aspects of SLL such as word meaning, sounds, and grammar during the early phase of SLL.

Interestingly, other studies have shown that a day-time nap has a positive, consolidating effect on language (i.e., vocabulary or word names) learning which exceeds effects of the same intensity of active rest or interfering activity, possibly due to the slow-wave sleep or REM sleep phases that are absent during mere rest. 

Furthermore, recent evidence suggests that a period of sleep such as a short nap after a motor learning task is a relevant factor for memory consolidation. Motor learning involves learning a skilled task and then practicing with a goal in mind until the skill is executed automatically. 

It turns out that naps also help learn and retain better new words and meanings. Not all learnt information is retained after sleep however and which memories benefit from sleep and which do not remains to be fully specified. There is increasing evidence that sleep works as a filter by predominantly strengthening memories that are adaptive or of relevance to the future