Language Development
Xinyue Tian
‍Sleep is a natural state in organisms characterized by an absence of consciousness along with the reduced muscle activation. It is necessary in higher vertebrates and critical for proper language development. Although sleep will take up a third of the average person's day, the purpose and mechanism of sleep are not completely clear. ‍Sleep is an active topic of interest in neuroscience as it seems to be crucial for many cognitive processes, including memory consolidation and learning. Inherently, sleep plays a large role in the early development of language as it is during sleep that changes in the brain are consolidated [‍1]‍. ‍These include but are not limited to‍ an increase in brain volume, rapid growth of grey matter and strengthening of neuronal connections [1]. It is suggested that newborns require about 18 hours of sleep per day for proper brain structure development [1]. Babies are equal or less than 3 years old require 15 hours of sleep per day for the success of language development [1]. ‍After 3 years old, children complete their development of mother tongue, and time for sleep decreases over year.‍ Which stage of sleep plays the most important role in language development remains unclear, but it is obvious to see that sleep in general is important, especially for infants’ language development.
Content
4.1 Changes in brain structure4.1a Introduction to basic brain structure
4.1b Neuron connection

4.2Language and cognitive function
4.2a Memory consolidation
4.2b Joint attention
4.2c Sleep behavior

4.3 Consequences in infants with OSAS

4.4 References

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Changes in Brain Structure




Introduction

The structure of brain is inspected visually using alcohol or other fixatives to immerse in. Visually, the interior of the brain consists of grey matter which is darker in color and white matter which is lighter in colour. In humans, brain weighs about 1.5 kg on average with 1130-1260 cm3 in size [12]. The largest part of a human brain as well as any primates’ is cerebral hemisphere which has a symmetrical division along the midline. It is constructed by a sheet of neural tissue which folds in a particular way in order to allow the largest surface area in the skull. Anatomically, cerebral cortex is divided into four lobes—frontal lobe, parietal lobe, occipital lobe and temporal lobe. Parietal lobe is the one that is responsible for various sensory functions related to language, such as hearing and attention [12]. Left and right hemispheres of parietal lobe carry out different aspects of functions in language [12]. Left hemisphere of parietal lobe processes symbolic function of language in reading and writing, while right hemisphere of parietal lobe process comprehension and understanding of language [12].

Neural Connection

There exist individual differences in the rate and extent of brain maturation associated with behavioral performance like language development [18]. It is important to consider individual variation of relation between brain structure and function in the typical developing population as well as atypical developing groups [18]. One of the modern brain imaging technologies that is used to investigate changes in brain structure during language developing stage is diffusion tensor imaging or DTI. DTI borrows the principle from magnetic resonance imaging technique which produces neural tract images by measuring the restricted diffusion of water in tissue []. It consists of a separate rate of diffusion and a preferred direction of diffusion in each voxel to produce a three-dimension image [18]. By using DTI, it reveals a positive relationship between the rate of maturation of white matter in the developing brain and myelination of axons which predicts the association between language development and enhanced neuronal connection. Language develops as more myelination formed, more neural signals transmitted and more fibres added to the white matter which all contributes in faster information processing and adding connections in the brain [18]

A distinct development of myelination is observed in newborns—it develops in the base of the brain, grows up toward corpus callosum, and then progresses forward to the anterior part of the brain [15]. When a child reaches age one, all the lobes begin the process of myelination except temporal lobe [17]. Language starts to develop in all children after age one and before age two which coincides with the timeline for lobs-myelination development. The degree of myelination predicts cognitive abilities, especially language acquisition, in infants at that stage of age.



Language and Cognitive Function



Memory Consolidation

Memory consolidation is defined as new memories are initially sensitive to disruption before going through the processes like glutamate release, protein synthesis, neural growth and neural rearrangement that makes the memory more stable progressively [1, 4]. There are three stages of memory processing that are identified—stabilization of memory, memory consolidation and memory recall. Memory consolidation mainly occurs during sleep associated with changes in hippocampus and certain stages of sleep. During sleep, neural activity remains high, especially in hippocampus. It is suggested that hippocampus exercises the information of contextual memories as well as episodic memories and consolidates memory from short-term storage into long-term [19]. Different types of memory consolidate during the specific stages of sleep. It appears that REM sleep is important in procedural memory consolidation, while Non-REM sleep is critical for episodic memory consolidation [19].
Sleep is proved to be necessary to consolidate certain types of memories, such as procedural memory. Sleep is critical to convert new temporal memories into long-term memories. Animal and human studies show that sleep deprivation has affection on memory task performance [8]. In general, sleep-deprived people had much more difficulty remembering in which of two sets of photos the faces had appeared [13]. Even though by using caffeine in sleep-deprived people to reduce their level of sleepiness and to improve their ability on the memory task, sleep-deprived people still performed significantly below the level of non-sleep-deprived people. It suggests that excessive daytime sleepiness due to sleep deprivation at night is an important risk factor for cognitive impairment [14].

By scanning the brains of sleep-deprived individual using fMRI and comparing them with non-sleep-deprived ones, it shows a reduced activity in the prefrontal cortex and an increased activity in parietal lobe for sleep-deprived people [5]. Also, sleep-deprived people show a decreased in left temporal lobe indicating slower language processing [5].

Joint attention

Joint attention is defined as the ability to coordinate attention with a social partner [9]. It is an indicator of the development of language. When joint attention does not develop properly early in life, infants show disruption in social cognition and language. Brian imaging studies using PET and EEG analysis show that infants with glucose metabolism in the left frontal cortex have better performance on joint attention task [9]. It is suggested that frontal lobe function may play a role in infant joint attention [10]. Left frontal and left and right central activation are associated with ability of joint attention in infants according to EEG studies [11]. Responding to joint attention involves activation in left parietal area and deactivation in right parietal area which are also involved in early attention shifting capacity in infants [11]. As language starts to be acquired by infants, different brain areas are being exercised accordingly.

Sleep behavior

Sleep consolidation is assessed using the ratios of day/night consecutive sleeping durations to investigate the effect on language development. It is suggested that poor sleep consolidation during the first 2 years of life is a risk factor for language learning, whereas good sleep consolidation enhances language learning [3].

Sleep and wakefulness in infants are recorded by their parent in order to examine their cognitive and language outcomes. It is suggested that circadian sleep regulation is associated with both mental development and language development in early childhood [2].

Sleep facilitates infants in learning about social cues and language. Infants conditioned to have a social stimulus show increased learning. It is suggested that learning about the social world occurs early in life which facilitate language learning [16].

Bedtime routine is used to investigate its associations with language development. Nighttime sleep duration and cognitive, behavioral, and health outcomes are included as predictors [6]. There exists a positive association between language-based bedtime routines and nighttime sleep duration. There exists an inversed association between language-based bedtime routine with behavior problems, and positive association with better general health. It is suggested that regular use of language-based bedtime routines, such as singing, reading, and storytelling at bedtime may have a lasting positive benefit for language development and cognitive development in children [6].

Consequence in Infant with OSAS


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OASA is short for obstructive sleep apnea syndrome. It is a sleep disorder characterized by abnormal pauses in breathing during sleep [7]. It is the most common sleep disorder seen in our population. Even though it is rare, it is possible for children to have obstructive sleep apnea syndrome and it is devastating for children, not only because children are more vulnerable to daytime sleepiness, but also because obstructive apnea syndrome can impair children with normal mental development as well as cognitive function development.
It has shown that behavioral and neurocognitive functions are impaired in children due to obstructive apnea syndrome. Children with OSAS show impairment in executive functions, attention, receptive vocabulary, and behavior problems [7]. It is suggested that the impact of OSAS on behavioral and cognitive functions begins in early childhood [7].

References


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