Environmental enrichment
Environmental enrichment is the stimulation of the
Research on animals finds that environmental enrichment could aid the treatment and recovery of numerous brain-related dysfunctions, including
Research on humans suggests that lack of stimulation delays and impairs cognitive development. Research also finds that attaining and engaging in higher levels of education, environments in which people participate in more challenging cognitively stimulating activities, results in greater cognitive reserve.
Early research
Also starting around 1960,
Synapses
Synaptogenesis
Rats raised with environmental enrichment have thicker cerebral cortices (3.3–7%) that contain 25% more
Dendrite complexity
Environmental enrichment affects the complexity and length of the dendrite arbors (upon which synapses form). Higher-order dendrite branch complexity is increased in enriched environments,[13][15] as can the length, in young animals, of distal branches.[16] Environmental enrichment rescues harmful effects of stress on dendritic complexity.[17]
Activity and energy consumption
Animals in enriched environments show evidence of increased synapse activation.[18] Synapses tend to also be much larger.[19] Gamma oscillations become larger in amplitude in the hippocampus.[20] This increased energy consumption is reflected in glial and local capillary vasculation that provides synapses with extra energy.
- Glial cell numbers per neuron increase 12–14%[5][7]
- The direct apposition area of glial cells with synapses expands by 19%[21]
- The volume of glial cell nuclei for each synapse is higher by 37.5%[18]
- The mean volume of mitochondria per neuron is 20% greater[18]
- The volume of glial cell nuclei for each neuron is 63% higher[18]
- Capillary density is increased.[22]
- Capillaries are wider (4.35 μm compared to 4.15 μm in controls)[18]
- Shorter distance exist between any part of the neuropil and a capillary (27.6 μm compared to 34.6 μm)[18]
These energy related changes to the neuropil are responsible for increasing the volume of the cerebral cortex (the increase in synapse numbers contributes in itself hardly any extra volume).
Motor learning stimulation
Part of the effect of environmental enrichment is providing opportunities to acquire
Maternal transmission
Environmental enrichment during pregnancy has effects upon the fetus, such as accelerating his or her retinal development.[25]
Neurogenesis
Environmental enrichment can also lead to the formation of neurons (at least in rats)[26] and reverse both the loss of neurons in the hippocampus and memory impairment from chronic stress.[27] However, its relevance has been questioned for the behavioral effects of enriched environments.[28]
Mechanisms
Enriched environments affect the expression of
Rehabilitation and resilience
Research in animals suggests that environmental enrichment aids recovery from certain neurological disorders and cognitive impairments. There are two mains areas of focus: neurological rehabilitation and cognitive reserve, the brain's resistance to the effects of exposure to physical, natural, and social threats. Although most of these experiments used animal subjects, mainly rodents, researchers have pointed to the affected areas of animal brains to which human brains are most similar and used their findings as evidence to show that humans would have comparable reactions to enriched environments. The tests done on animals are thus meant to represent human simulations for the following list of conditions.
Neurological rehabilitation
Autism
A study conducted in 2011 led to the conclusion that environmental enrichment vastly improves the cognitive ability of children with
Alzheimer's disease
Through environmental enrichment, researchers were able to enhance and partially repair memory deficits in mice between ages of 2 to 7 months with characteristics of Alzheimer's disease. Mice in enriched environments performed significantly better on object recognition tests and the Morris Water Maze than they had when they were in standard environments. It was thus concluded that environmental enrichment enhances visual and learning memory for those with Alzheimer's.[42] Furthermore, it has been found that mouse models of Alzheimer's disease that were exposed to enriched environment before amyloid onset (at 3 months of age) and then returned to their home cage for over 7 months, showed preserved spatial memory and reduced amyloid deposition at 13 months old, when they are supposed to show dramatic memory deficits and amyloid plaque load. These findings reveal the preventive, and long-lasting effects of early life stimulating experience on Alzheimer-like pathology in mice and likely reflect the capacity of enriched environment to efficiently stimulate the cognitive reserve.[43] A human study suggests that enriched gardens contribute to better cognitive function and independence in activities of daily living, compared to conventional sensory gardens.[44]
Huntington's disease
Research has indicated that environmental enrichment can help relieve motor and psychiatric deficits caused by
Parkinson's disease
Multiple studies have reported that environmental enrichment for adult mice helps relieve neuronal death, which is particularly beneficial to those with Parkinson's disease.[46] A more recent study shows that environmental enrichment particularly affects the nigrostriatal pathway, which is important for managing dopamine and acetylcholine levels, critical for motor deficits.[47] Moreover, it was found that environmental enrichment has beneficial effects for the social implications of Parkinson's disease.[47]
Stroke
Research done in animals has shown that subjects recovering in an enriched environment 15 days after having a stroke had significantly improved neurobehavioral function. In addition these same subjects showed greater capability of learning and larger infarct post-intervention than those who were not in an enriched environment. It was thus concluded that environmental enrichment had a considerable beneficial effect on the learning and sensorimotor functions on animals post-stroke.[48] A 2013 study also found that environmental enrichment socially benefits patients recovering from stroke. Researchers in that study concluded that stroke patients in enriched environments in assisted-care facilities are much more likely to be engaging with other patients during normal social hours instead of being alone or sleeping.[49]
Rett syndrome
A 2008 study found that environmental enrichment was significant in aiding recovery of motor coordination and some recovery of BDNF levels in female mice with conditions similar to those of Rett syndrome. Over the course of 30 weeks female mice in enriched environments showed superior ability in motor coordination to those in standard conditions.[50] Although they were unable to have full motor capability, they were able to prevent a more severe motor deficit by living in an enriched environment. These results combined with increased levels of BDNF in the cerebellum led researchers to conclude that an enriched environment that stimulates areas of the motor cortex and areas of the cerebellum having to do with motor learning is beneficial in aiding mice with Rett syndrome.[50]
Amblyopia
A recent study found that adult rats with amblyopia improved visual acuity two weeks after being placed into an enriched environment.[51] The same study showed that another two weeks after ending environmental enrichment, the rats retained their visual acuity improvement. Conversely, rats in a standard environment showed no improvement in visual acuity. It was thus concluded that environmental enrichment reduces GABA inhibition and increases BDNF expression in the visual cortex. As a result, the growth and development of neurons and synapses in the visual cortex were much improved due to the enriched environment.[51]
Sensory deprivation
Studies have shown that with the help of environmental enrichment the effects of sensory deprivation can be corrected. For example, a visual impairment known as "dark-rearing" in the visual cortex can be prevented and rehabilitated. In general, an enriched environment will improve, if not repair, the sensory systems animals possess.[52]
Lead poisoning
During development, gestation is one of the most critical periods for exposure to any lead. Exposure to high levels of lead at this time can lead to inferior spatial learning performance. Studies have shown that environmental enrichment can overturn damage to the hippocampus induced by lead exposure.[53] Learning and spatial memory that are dependent on the long-term potentiation of the hippocampus are vastly improve as subjects in an enriched environments had lower levels of lead concentration in their hippocampi. The findings also showed that enriched environments result in some natural protection of lead-induced brain deficits.[53]
Chronic spinal cord injuries
Research has indicated that animals suffering from
Maternal deprivation stress
Maternal deprivation can be caused by the abandonment by a nurturing parent at a young age. In rodents or nonhuman primates, this leads to a higher vulnerability for stress-related illness.[55] Research suggests that environmental enrichment can reverse the effects of maternal separation on stress reactivity, possibly by affecting the hippocampus, the amygdala and the prefrontal cortex.[55][17]
Child neglect
In all children, maternal care is one of the significant influences for hippocampal development, providing the foundation for stable and individualized learning and memory. However, this is not the case for those who have experienced child neglect. Researchers determined that through environmental enrichment, a neglected child can partially receive the same hippocampal development and stability, albeit not at the same level as that of the presence of a parent or guardian.[56] The results were comparable to those of child intervention programs, rendering environmental enrichment a useful method for dealing with child neglect.[56][failed verification]
Cognitive reserve
Aging
Decreased hippocampal neurogenesis is a characteristic of
Prenatal and perinatal cocaine exposure
Research has shown that mice exposed to environmental enrichment are less affected by the consequences of
Humans
Though environmental enrichment research has been mostly done upon rodents, similar effects occur in primates,
Localized cerebral cortex changes
MRI detects localized
Institutional deprivation
Children that receive impoverished stimulation due to being confined to cots without social interaction or reliable caretakers in low quality
Such children show marked differences in their brains, consistent with research upon experiment animals, compared to children from normally stimulating environments. They have reduced brain activity in the
Conversely, enriching the experience of
Cognitive reserve and resilience
Another source of evidence for the effect of environment stimulation upon the human brain is cognitive reserve (a measure of the brain's resilience to cognitive impairment) and the level of a person's education. Not only is higher education linked to a more cognitively demanding educational experience, but it also correlates with a person's general engagement in cognitively demanding activities.[71] The more education a person has received, the less the effects of aging,[72][73] dementia,[74] white matter hyperintensities,[75] MRI-defined brain infarcts,[76] Alzheimer's disease,[77][78] and traumatic brain injury.[79] Also, aging and dementia are less in those that engage in complex cognitive tasks.[80] The cognitive decline of those with epilepsy could also be affected by the level of a person's education.[81]
See also
Notes
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- ^ Mary Brophy Marcus (June 5, 2013). "'Sensory-Focused' Autism Therapy Shows Early Promise". webmd.com.
- ^ Nkoyo Iyamba (October 9, 2014). "Autism treatment gives Utah family hope". ksl.com. Archived from the original on September 25, 2015.
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