How Enriched Environments Benefit The Brain (page 5)
Animal studies have found that enriched environments can induce important changes in the brain, including enhanced functioning and development in areas related to cognitive capacity, learning, memory, and resilience. Depending on the design of the study, the results might include more neurons, longer dendrites, more connections, heavier brains, greater brain mass, more intra- and intercortex connectivity, and enlarged capillaries. Changed brains can be contrasted with a control group and measured in many ways.
To understand, measure, and validate these changes, researchers use a variety of both "old school" methods and very smart new ones. These include
- Behavioral tasks such as running a radial arm maze or swimming in a Morris water maze
- Brain scans such as an MRI to measure changes in tissue volume
- Use of marker dyes such as a green fluorescent protein that glows when a cell divides to show increased new cell generation
- Autopsies, which can reveal precise measurements of brain weight, cell-to-cell connectivity, or even the density of synapses
Enhanced environmental stimulation can affect the brain in many ways. To simplify the discussion here, I'll focus on six fundamentally different effects. They are consistent—and for every study I describe, there are many others with similar findings.
- Metabolic allostasis: Changes in blood flow, baseline chemical levels, and metabolic functioning
- Enhanced anatomical structures: Larger neurons and more developed cell structures
- Increased connectivity: Increased circuitry and branching from one neuron to another
- Responsiveness and learning efficiency: Enhanced electrical signaling, cell efficiency, and neural processing
- Increased neurogenesis and growth factors: Production of new brain cells as well as special proteins important for the brain's survival
- Recovery from trauma and system disorders: Protection from stress and greater capacity to heal when damaged
It is true that any of these changes can (and sometimes do) happen without efforts to enhance the environment. But it is the degree, the rate, and the complexity of change that differentiate efforts at environmental enrichment from other, more basic, learning or maturational processes. The studies reliably show that changes do occur from enhanced environmental efforts.13 In many cases, they can facilitate what seem like miracles. For the moment, suffice it to say that there are many verifiable and enticing benefits to the enrichment process. When taken as a whole, they really do seem remarkable.
The word allostasis refers to a resetting or readjustment of baseline brain levels. Environmental stimulation can enhance blood flow in the brain as well as boost levels of chemicals important to learning, mood, and cognition. The first group of relevant studies were by neuroscientist Matti Saari, whose group in Canada has shown changes in regional cerebral metabolism.14 In addition, his group found that these changes in blood flow are regionally specific to the thalamic, cortical, and hippocampal areas.15 Those areas play critical roles in learning, consciousness, and memory, and we must pay close attention to the results.
Another area of high interest is the neurotransmitters, a group of chemicals that includes erotonin and dopamine. These are essential for learning, mood, memory, and communication within the brain. Animal studies have found that levels of these chemicals can be altered as a result of enrichment efforts. Acetylcholine, a common neurotransmitter known to help with memory formation, also increases in enrichment studies.16 Remarkably, enrichment exercise can even enhance activity of opioid (pleasure and analgesic) sites.17 Enrichment efforts can help regulate serotonin to enhance mood and improve cognitive flexibility.18 This research is highly relevant because of the relationship to stress and stress disorders.
Studies show that rats getting an enrichment protocol gain some protection from stress disorders. In fact, it can lead to pronounced changes in neuroendocrine regulation compared with those in a more basic control environment.19 The enrichment protocols decrease the release of stress-responsive hormones.20 In addition, enrichment studies support the reversal of social isolation, too.21
Researchers find, as a result of changes in specific chemicals, a reduction in nonhuman primate aggression from an enrichment effect in the environment.22 These are all positive effects from essential brain chemicals that can improve mood, memory cognition, or both. Most teachers would be ecstatic to have students with enhancements in these areas.
Enhanced Anatomical Structures
Scientific studies have shown that nearly every indicator of optimal brain functioning improves with successful enrichment. Enrichment involves changes in the physical brain, and these enhanced anatomical structures may provide the scaffolding necessary for increased cognitive tasks. In fact, enrichment pioneer Bill Greenough has shown that enrichment protocol efforts increase the brain's vascular system, which increases oxygen to the neurons.23 He also confirmed increases in the number of glial cells, which interact closely with neurons.24
Neuroscientist Marian Diamond has shown a number of enrichment effects, including a thicker cortex and increases in the size of neurons (Figure 3.4).25 Besides Diamond's studies showing increases in glial cells and in cortical depth, various researchers have found increased dendritic length, and more complex (higher order) branching on the dendrites, better enabling them to make more future connections.26 It sounds like all of these changes would add mass to the brain, and they do. Brain weights also increase with enrichment.27 These effects are robust and have correlated with overall brain weight increases of 7 to 10 percent after 60 days.28
Enrichment studies show development of new circuitry in the brain. The evidence for increased connectivity comes from seeing changes as a result of neurons "talking" to each other, creating new synapses (Figure 3.5). First, there are studies showing changes in the necessary dendritic branching for connectivity in multiple areas of the brain, including the visual area.29 And more important, there is an increase in synapses from new connections and dendritic spine counts.30 More dendrites per neuron and more synapses per neuron are correlated with increased connectivity. This result occurs in animals given enrichment protocols compared with those raised in isolation or non-social environments.31 This increased connectivity and mapping may be important to cognition and processing.
Connectivity is a tricky issue because there are competing models of how this occurs. Bill Greenough and his colleagues at the University of Illinois, Champagne-Urbana, have shown that motor learning induces the formation of new synapses in mouse models.32 But seven years later another study showed that associative learning changes the size of existing synapses, possibly facilitating neurotransmission. Yet it does not increase the number of synapses in the hippocampus.33 This contrasting set of data suggests there may be developmental phases in which the same stimulus produces altogether different results. It may also be a case of differences in brain geography; getting the effect in one area of the brain (versus another) may do the job better or in a more timely way.
Responsiveness and Learning Efficiency
On each side of our heads, near our ears, are our temporal lobes. The hippocampus is buried deep within our temporal lobes, and we have two of these C-shaped structures. Studies suggest that the tissue in the hippocampus, an area associated with learning and memory, becomes better at electrical signal conduction points.34 The field potentials of synapses in the hippocampus increase with enrichment effects.35 Cells in enriched rats also showed an increased capacity for plasticity.36 These changes can influence our senses, too. Studies show an improvement in the capabilities of our auditory processing, and we can even spur the development of the visual system.37
Another astonishing factor of an enriched environment is that it influences protein synthesis and gene transcription. Rats show higher levels for the messenger RNA, which is essential for memory.38 After frequent stimulation, neurons change and become more responsive. An enriching environment may support the process of long-term potentiation, meaning it enhances the very processes by which learning takes place. It also improves memory.39 We see rats that perform mazes better, remember spatial cues better, and learn faster.40 Taken together, the electrophysiological data suggest that the brain can make activations easier and more often, a function associated with new learning and plasticity.
Increased Neurogenesis and Growth Factors
Recent studies show that adult lab animals (and humans) generate new brain cells (neurogenesis) and that enrichment efforts can accelerate this process. In elderly mice exposed to an environmentally complex housing condition, the quantity of new brain cells generated was not 10, 20, or 50 percent higher, but a whopping 500 percent higher than for the nonenriched control group.41 As early as 1998, researcher Gerd Kempermann discovered that rats grew brand new brain cells every day. By use of an ingenious staining technique, involving a green fluorescent protein extracted from jellyfish, his team was able to identify and photograph newly dividing neurons. And in a later study, Kempermann, a Swede working with San Diegan Fred Gage at the Salk Institute in La Jolla, California, got permission to inject the same dye into the brains of elderly Swedish patients with inoperable cancer. When the patients eventually died from cancer in the following months, Kempermann and Gage were able to autopsy the brains and verify that humans can and do grow new brain cells.42 Additional groundbreaking research has shown not only that humans do grow new neurons but that the rate of growth can be increased by enrichment efforts.43
Growth factors are critical chemicals that regulate and support the growth and survival of brain cells and have been linked to increased rates of cognition.44 Research has shown an increase in gene expression for brain-derived neurotrophic factors in songbirds after exposure to an enriching environment, and an increase in an insulin-like growth factor was also found in enriched rats.45 These growth factors are linked to the proliferation, survival, and functionality of new neurons. Rats in enriching environments had significantly higher survival rates (85 percent) of new neurons compared with the control and other experimental conditions, in which rates ranged from 42 percent to 56 percent.46 What does all this lead to? It seems to be the daily positive environmental influences on the subject over the long haul that are critical for enrichment, not just the one-time burst of activity.
Figure 3.6 summarizes the current understanding about a key role for neurogenesis. The production of new neurons is partly genetic and partly modifiable by human experience. We not only can alter our behaviors to produce more new neurons (which are correlated with learning, mood, and memory) but can enhance their survival changes with behavioral modifications using enrichment protocols.
Recovery from Trauma and System Disorders
Many animal studies suggest that enrichment effects can influence recovery from genetic disorders, trauma, and brain impairments. Mice bred for slower learning (variety 129/SvJ) are known to do worse on maze tasks, and they have lower neuronal production than do their genetically bred typical counterparts.47 But they improved dramatically in an enhanced environment in two ways: neurogenesis and learning performance.48
In rodents with neonatal binge alcohol exposure, enrichment efforts improved learning dramatically.49 Early environmental neglect causes profound neural and behavioral effects. Animals reared in isolation show increased anxiety and poorer performance in learning and spatial memory tasks. But later enrichment efforts reverse some or all of the deficits induced by isolation rearing.50 In addition, environmental enrichment leads to a functional reversal of the effects of maternal separation through the development of neural compensation.51 The negative effects of a stressful social experience can affect us even at the micro level of our cells.
At Duke University, experimenters showed that an enriching environment could override even a genetic mutation in mice that caused obesity.52 One advantage of these types of animal studies is that a disability can be induced, and the animal can be placed in study to determine if an enhanced environment can help in rehabilitation. That's been done quite often. Humans suffer a variety of challenging brain insults. But the good news is that some of these problems have been induced and repaired with enrichment in mice models.
Enrichment benefits have been found when there's exposure to environmental lead, debilitating head injuries, alcoholism, stroke, and toxic exposure.53 Studies with contrasting environments show that those in an enriched condition have more protective strengths and recover faster from exposure to injury.54 These results are found in the enriched condition as compared with those in the standard or control condition. These studies collectively suggest that we may be able to facilitate learning-underperforming and special needs learners with an enrichment program.