The acquired environment plays a very important role in brain development and brain injury repair; a favorable environment promotes brain development and brain injury repair, while an unfavorable environment does the opposite.
I. Basic research
1.Neuroplasticity
Neuroplasticity is the modifiability of the central nervous system in terms of morphological structure and functional activity. From the cellular and molecular mechanisms of synapses in the genus Drosophila to the recovery from stroke in the elderly, there is neuroplasticity. The immature brain is plastic during development, and after maturation, neural circuits remain variable, modifiable, or plastic throughout life in order to adapt to various internal and external environmental changes, such as after neurological injury or aging. Neuroplasticity is mainly manifested in synaptic plasticity.
Synaptic plasticity is divided into structural plasticity and functional plasticity. Synaptic structural plasticity refers to changes in synaptic morphology and the formation of new synaptic connections and the establishment of transmission functions, and is a long-lasting plasticity. Synaptic functional plasticity refers to the increase or decrease of synaptic transmission efficiency due to repeated synaptic activity, including long term potentiation (LTP) and long term depression (LTD), which are considered to be the basis of learning and memory. In addition, the gradual reduction or transformation of silent synapses into functional synapses also plays an important role.
2. Postnatal environment
In the study of animals, the acquired environment includes rich environment, standard environment and solitary environment. Standard environment refers to a standard rat cage housing 3-6 rats. Solitary environment is to keep only one rat in a very small cage. Enriched environment means that 8-12 rats are kept in a larger cage and different colored and shaped objects are placed inside the cage, such as turntables, pipes, ramps, rings and toys, etc., which are changed and adjusted regularly to create new and different stimuli, so as to provide fuller opportunities for multi-sensory stimulation, active movement and emotional experience.
3. Effects of enriched environment on neuroplasticity after brain injury
3.1 Structural plasticity
Studies have confirmed that the enriched environment can cause changes in the morphological structure of the nervous system. Many injurious stimuli such as cerebral hypoxia, cerebral ischemia, traumatic brain injury, intracranial infection and poisoning can reduce neurological plasticity and cause different degrees of brain dysfunction. The administration of environmental enrichment stimuli can reduce the degree of hemispheric damage, inhibit neuronal apoptosis, and increase the number of dendritic branches and lateral spines in non-injured areas, thus enhancing the compensatory plasticity of neurons. In genetically mutant mice with NMDA receptor 1 gene removed from the hippocampal CA1 region by transgenic technology, their learning and memory abilities were significantly impaired, and their hippocampal synaptic density increased and dendritic spines increased after enriched environmental stimulation, and their learning and memory abilities were enhanced.
The number of dendritic branches and spines of neurons in the contralateral cortical area of the infarct was increased after 1 week in the enriched environment in rats with primary hypertension following middle cerebral artery infarction compared with rats housed in the standard environment. The enriched environment also induced plasticity in astrocytes, which have an important role in brain injury recovery by phagocytosing harmful neurotransmitters, maintaining the stability of the brain microenvironment, secreting neurotrophically active substances, and preventing further damage to neuronal cells after ischemia in the early stages of brain injury. The results of ultrastructural studies showed that cortical astrocytes in rats fed in a rich environment showed a trend of rapid changes and a significant increase in the connections between astrocytes and synapses.
3.2 Functional plasticity
Synaptic plasticity is often associated with altered behavioral functions, and enriched environmental stimuli can compensate for the impairment and neurodegeneration caused by brain damage. Various animal models of brain damage have been simulated and given enriched environmental stimuli, and it has been found that enriched environments improve brain function in experimental animals and enhance their problem-solving abilities in complex behavioral tests.
Administration of enriched environmental stimuli promotes recovery of brain function to some extent, mainly in the form of enhanced sensorimotor function and learning and memory abilities. When rats with hypoxic-ischemic brain injury were given early touch and enriched environmental stimulation, sensory-motor function and behavioral tests were performed, and the non-intervention group had poorer discriminative learning ability and sensory-motor function than the intervention group and normal control group, while there was no significant difference between the intervention group and normal control group. The results indicated that environmental stimulation could improve sensorimotor function and discriminative learning ability in rats with hypoxic-ischemic brain injury, and effectively reduce the incidence of brain dysfunction. Electrophysiological studies confirmed that environmental stimulation was associated with hippocampal LTP production, which could enhance the plasticity of the central nervous system and the learning memory ability.
After giving motor rehabilitation training to rats with cerebral infarction, the formation of learned LTP in the hippocampal CA3 area synaptic effect in the rehabilitation group was significantly faster than that in the model group without any training, which improved the learning efficiency and promoted the recovery of learning memory. It has been found that even when physical brain damage is recovered, cognitive deficits persist and affect the quality of life of those with chronic conditions, with spatial navigation and memory deficits lasting for months after injury, and that non-invasive environmental stimulation is beneficial in reducing cognitive deficits and maintaining tissue integrity. Among behavioral tests, the most classically applied is the water maze test, which is closely linked to spatial learning memory. For example, rats in a state of vertigo after epilepsy showed improved cognitive performance in the water maze test after 28 days of enriched environmental stimulation, although there were no differences in EEG and brain morphological changes.
4. Mechanism of acquired stimulation and neuroplasticity
The effect of acquired stimulation on the nervous system is a complex process in which many factors are involved. Current studies have mainly explored the effects of acquired stimulation on brain development and repair of developmental brain damage from both morphological and behavioral aspects, but the mechanisms are not yet understood. It has been shown that enriched environmental stimulation induces the expression of neurotrophic factor mRNA in the brain, especially increasing the amount of nerve growth factor and the density of nerve growth factor receptors, which have important roles in both the developing brain and brain injury repair.
Focal cerebral ischemia in rats placed in an enriched environment resulted in an upregulation of NGF expression in the brain 2-7 days after ischemia.NGF expression is dependent on the activation of excitatory glutamate such as NMDA, AMPA and KA receptors, signaling pathways involved in prolonged changes in cell morphology.Activation of NMDA receptors is known as a molecular switch for learning memory. The sensitivity and expression of NMDA receptors are increased after enrichment of environmental stimuli, and their function is dependent on their subunit components. Studies on models of cerebral ischemia have found that environment-dependent effects are associated with the density of AMPA and KA receptor binding in the ischemic contralateral cortex, and the latter two are linked to the maintenance of a functional recovery state after ischemia.
Hippocampal AMPA receptors mediate the blockade of spatial memory impairment and may be involved in compensatory mechanisms after injury to the extent that they can overcome the impairment of spatial memory. AMPA receptor binding areas in hippocampal subregions were associated with swimming speed in the water maze test. AMPA receptors were increased after enriched environment stimulation, and it plays an important role in synaptic plasticity induced by repetitive activity; another scholar found that enriched environment reduced the expression of nuclear transcription factor AP-2 gene in hippocampal CA1 and CA3 regions by 31% and 67%, respectively, compared with solitary environment , and the AP-2 site is in the promoter region of the gene, while the promoter of GC-Rs gene contains the same sequence as the bound The AP-2 locus is in the promoter region of the GC-Rs gene and the GC-Rs gene promoter contains homologous sequences to the bound GC, therefore it is hypothesized that AP-2 may be involved in mediating the effects of environmental factors on hippocampal GC-Rs gene expression.
In addition, environmental stimuli can affect the function of the hypothalamic pituitary-adrenal axis. Activation of salt corticosteroids (type I, MR) induces LTP production, and hippocampal MR levels are associated with cognitive function. Increased expression of glucocorticoid (type II, GR) receptors after enriched environmental stimulation improves neuroplasticity in rats after injury on the one hand, while excessive and delayed GR activation increases neuronal vulnerability on the other hand. Stimulation of rats with prenatal stress in an enriched environment showed a diminished hypothalamic-pituitary-adrenal axis response to stress, prolonged corticosterone secretion, and improvement in their social behavior. Early touch in neonatal rats reduced glucocorticoid levels in vivo, thereby reducing its damage to the hippocampus, and had a facilitative effect on the learning memory capacity of rats as they entered old age.
In addition, enrichment of the environment increased the activity of inducible and neuronal nitric oxide synthase in the brain and increased the expression of apoptosis-regulating genes in the hippocampus such as cysteine proteases (caspases) and bcl-2 family genes, which block cell death in the CA1 region of the hippocampus after global cerebral ischemia and promote the development of nerve fiber myelin in the brain, thereby affecting the central nervous system after injury The repair process of
Second, the postnatal environment of neonatal brain injury
The use of various good motor patterns and stimuli, the establishment of appropriate sensory information input, and the promotion of the shaping and optimization of brain structure and function are the theoretical basis of the postnatal environment intervention for brain injury in the neonatal period.
1.Objectives
1.1 To improve muscle tone.
1.2 Enhance the role of flexor muscles.
1.3 Improve the quality of spontaneous movements.
1.4 Improve orientation to the median line.
1.5 Promote head-turning positive reflex.
1.6 Improve muscle status.
1.7 Improves the audiovisual reflex.
1.8 Normalize the sensorimotor experience.
2., Environmental requirements and intervention guidance
2.1 Prone position: prone position, so that the infant’s center of gravity leans forward to reach the vicinity of the cheek, can enhance the stimulation of neck and trunk extension, tactile and proprioceptive sensations. Lateral recumbency can improve the midline and flexor response, and the side-lying position with left and right exchange can promote the development of left and right symmetrical posture and movement. The supine position facilitates the development of normal activity patterns in newborns. Butterfly or U-shaped pillow is more conducive to the development of postural patterns in the infant’s recumbent position.
2.2 Tactile stimulation: The mouth, palms and soles are very sensitive to touch and are the parts of the body that emphasize stimulation. Stimulation of the perioral area, i.e., massage from the temporomandibular joint to the mouth and the application of appropriate pressure to the upper lip. Stimulation of the palms of the hands and soles of the feet means applying some pressure and massage to the palms of the hands and soles of the feet. Weight bearing and other forms of proprioceptive stimulation can restore and normalize the function of the infant’s tactile system. Tense swaddling and slow-paced gentle strokes are effective in calming an over-stressed infant and can calm the infant; rapid irregular movements are beneficial in making the infant awake or alert. Touching the skin with the entire palm of the hand, rather than just the tips of the fingers, will help calm the newborn from irritability. Skin-to-skin contact is a positive experience for the infant and makes for better sensory input than using comforters or fingers in the mouth.
2.3 Visual and auditory: Stimulate the visual development of newborns can be used mirrors, pictures of human faces, human face toys, distance control at 18-20cm; infants like human voice, female than male voice is more acceptable to infants, and the mother’s voice environment is the best.
2.4 Taste: newborns like sweet taste and less like bitter or salty taste.
2.5 Hammock suspension technique: This technique stimulates the vestibular system, thus improving alertness and behavior, and also promotes elongation of the neck and trunk extensors, activation of the anterior cervical and abdominal muscle systems, and increased midline activity in the distal upper extremities, normalizing motor development. The hammock always elicits active movements and increases vestibular sensory input.
2.6 Carrying techniques: develop flexion and midline fixation by gently rocking the infant in the flexion of the arms; the infant should be carried bilaterally in order to develop motor and postural equilibrium.
2.7 NICU: Pay attention to appropriate lighting and noise, and provide opportunities for spontaneous movement of the newborn. Staff can reduce excessive light exposure by covering the infant’s incubator with a shade cloth, and can reduce noise by closing the incubator door so that the infant’s NICU environment is more like that of the womb. Special attention should be paid to the infant’s visual and auditory senses in the NICU, which are already in a state of over-stimulation, while the real deficit is the infant’s tactile and vestibular sensory stimulation.
2.8 Feeding issues.
It is important to understand the neonatal oral motor reflexes and the underlying pathological patterns. The developmental status of the infant’s oromotor reflex should be assessed prior to oral feeding. The gag reflex is a basic reflex to counteract aspiration, and if the gag reflex is hyperactive, the infant may not accept the nipple. Assessment includes tongue movements, foraging reflexes, and sucking reflexes. A quiet and alert state is beneficial for feeding.
Non-nutritive sucking can strengthen the sucking reflex. It is important to assess the strength and rhythm of their sucking. It is also important to assess whether the infant moves the tongue back and forth in a coordinated manner, closes the lips to prevent fluid from leaking out of the mouth, and breathes naturally while eating. If tongue uplift during sucking is difficult, the infant’s ability to eat should be stimulated and facilitated by applying appropriate pressure to the pacifier, either upward (palate direction) or downward (tongue direction).
Mouth movement techniques can promote lip closure, jaw stabilization, and improved sucking and swallowing function. In addition, the appropriate pacifier should be selected according to the infant’s sucking power, endurance and preference. Pacifiers come in different sizes, flow rates and flexibility. Using a soft pacifier can make it difficult for infants to learn to hold more liquid in their mouths, which can interfere with the development of feeding skills. Using a harder pacifier establishes a better sucking pattern and strengthens the muscles in the neck and mouth area.