Environmental enrichment (neural)
Encyclopedia
Environmental enrichment concerns how the brain
is affected by the stimulation of its information processing
provided by its surroundings (including the opportunity to interact socially). Brains in richer, more stimulating environments, have increased numbers of synapses
, and the dendrite arbors upon which they reside are more complex. This effect happens particularly during neurodevelopment, but also to a lesser degree in adulthood. With extra synapses there is also increased synapse activity and so increased size and number of glial energy support cells. Capillary vasculation
also is greater to provide the neurons and glial cells with extra energy. The neuropil
(neurons, glial cells, capillaries, combined together) expands making the cortex thicker. There may also exist (at least in rodents) more neurons
.
Research in nonhuman animals finds that more stimulating environment could aid the treatment and recovery of a diverse variety of brain related dysfunctions, including Alzheimer’s disease and those connected to aging, whereas a lack of stimulation might impair cognitive development.
Research upon humans suggests that lack of stimulation (deprivation—such as in old-style orphanages) delays and impairs cognitive development. Research also finds that higher levels of education (which is both cognitively stimulating in itself, and associates with people engaging in more challenging cognitive activities) results in greater resilience (cognitive reserve
) to the effects of aging and dementia.
who compared single rats in normal cages, and those placed in ones with toys, ladders, tunnels, running wheels in groups. This found that growing up in enriched environents affected enzyme cholinesterase
activity. This work led in 1962 to the discovery that environmental enrichment increased cerebral cortex
volume. In 1964, it was found that this was due to increased cerebral cortex thickness and greater synapse
and glial numbers.
Also starting around 1960, Harry Harlow
studied the effects of maternal and social deprivation
on rhesus monkey infants (a form of environmental stimulus deprivation). This established the importance of social stimulation for normal cognitive
and emotional development.
ones (that are usually interneurons). It also can affect neurons outside the brain in the retina
.
arbors (upon which synapses form). Higher-order dendrite branch complexity is increased in enriched environments, as can the length, in young animals, of distal branches.
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).
has effects upon the fetus
such as accelerating its retinal development.
(at least in rats) and reverses the loss of neurons in the hippocampus
and memory impairment following chronic stress. However, its relevance has been questioned for the behavioral effects of enriched environments.
in the cerebral cortex and the hippocampus that determine neuronal structure. At the molecular level, this occurs through increased concentrations of the neurotrophins NGF
, NT-3, and changes in BDNF. This alters the activation of cholinergic
neurons, 5-HT, and beta-adrenolin
. Another effect is to increase proteins such as synaptophysin
and PSD-95
in synapses. Changes in Wnt signaling
have also been found to mimic in adult mice the effects of environmental enrichment upon synapses in the hippocampus. Increase in neurons numbers could be linked to changes in VEGF
.
expansion after people learn complex tasks such as mirror reading (in this case in the right occipital cortex), three-ball juggling (bilateral mid-temporal
area and left posterior intraparietal sulcus
), and when medical students intensively revise for exams (bilaterally in the posterior and lateral parietal cortex). Such changes in gray matter volume can be expected to link to changes in synapse numbers due to the increased numbers of glial cells and the expanded capillary vascularization needed to support their increased energy consumption.
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 orbital prefrontal cortex
, amygdala
, hippocampus
, temporal cortex, and brain stem
. They also showed less developed white matter
connections between different areas in their cerebral cortices, particularly the uncinate fasciculus
.
Conversely, enriching the experience of preterm infants
with massage
quickens the maturating of their electroencephalographic
activity and their visual acuity
. Moreover, as with enrichment in experimental animals, this associates with an increase in IGF-1.
(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 generally engaging in cognitively demanding activities. The more education a person has received, the less the effects of aging, dementia, white matter hyperintensities, MRI-defined brain infarcts, Alzheimer’s disease, and traumatic brain injury. Also, aging and dementia are less in those that engage in complex cognitive tasks. The cognitive decline of those with epilepsy could also be affected by the level of a person’s education.
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
is affected by the stimulation of its information processing
Information processing
Information processing is the change of information in any manner detectable by an observer. As such, it is a process which describes everything which happens in the universe, from the falling of a rock to the printing of a text file from a digital computer system...
provided by its surroundings (including the opportunity to interact socially). Brains in richer, more stimulating environments, have increased numbers of synapses
Synaptogenesis
Synaptogenesis is the formation of synapses. Although it occurs throughout a healthy person's lifespan, an explosion of synapse formation occurs during early brain development...
, and the dendrite arbors upon which they reside are more complex. This effect happens particularly during neurodevelopment, but also to a lesser degree in adulthood. With extra synapses there is also increased synapse activity and so increased size and number of glial energy support cells. Capillary vasculation
Capillary
Capillaries are the smallest of a body's blood vessels and are parts of the microcirculation. They are only 1 cell thick. These microvessels, measuring 5-10 μm in diameter, connect arterioles and venules, and enable the exchange of water, oxygen, carbon dioxide, and many other nutrient and waste...
also is greater to provide the neurons and glial cells with extra energy. The neuropil
Neuropil
In neuroanatomy, a neuropil, which is sometimes referred to as a neuropile, is a region between neuronal cell bodies in the gray matter of the brain and blood-brain barrier . It consists of a dense tangle of axon terminals, dendrites and glial cell processes...
(neurons, glial cells, capillaries, combined together) expands making the cortex thicker. There may also exist (at least in rodents) more neurons
Neurogenesis
Neurogenesis is the process by which neurons are generated from neural stem and progenitor cells. Most active during pre-natal development, neurogenesis is responsible for populating the growing brain with neurons. Recently neurogenesis was shown to continue in several small parts of the brain of...
.
Research in nonhuman animals finds that more stimulating environment could aid the treatment and recovery of a diverse variety of brain related dysfunctions, including Alzheimer’s disease and those connected to aging, whereas a lack of stimulation might impair cognitive development.
Research upon humans suggests that lack of stimulation (deprivation—such as in old-style orphanages) delays and impairs cognitive development. Research also finds that higher levels of education (which is both cognitively stimulating in itself, and associates with people engaging in more challenging cognitive activities) results in greater resilience (cognitive reserve
Cognitive reserve
The term cognitive reserve describes the mind's resilience to neuropathological damage of the brain. The mind's resilience is evaluated behaviorally, whereas the neuropathological damage is evaluated histologically, although damage may be estimated using blood-based markers and imaging methods...
) to the effects of aging and dementia.
Early research
Donald O. Hebb in 1947 found that rats raised as pets performed better on problem solving tests than rats raised in cages. His research, however, did not investigate the brain nor use standardized impoverished and enriched environments. Research doing this first was started in 1960 by Mark RosenzweigMark Rosenzweig
Mark Richard Rosenzweig was an American research psychologist who found in animal studies on neuroplasticity that the brain continues developing anatomically, reshaping and repairing itself into adulthood based on life experiences, overturning the conventional wisdom that the brain reached full...
who compared single rats in normal cages, and those placed in ones with toys, ladders, tunnels, running wheels in groups. This found that growing up in enriched environents affected enzyme cholinesterase
Cholinesterase
In biochemistry, cholinesterase is a family of enzymes that catalyze the hydrolysis of the neurotransmitter acetylcholine into choline and acetic acid, a reaction necessary to allow a cholinergic neuron to return to its resting state after activation.-Types:...
activity. This work led in 1962 to the discovery that environmental enrichment increased cerebral cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
volume. In 1964, it was found that this was due to increased cerebral cortex thickness and greater synapse
Synapse
In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell...
and glial numbers.
Also starting around 1960, Harry Harlow
Harry Harlow
Harry Frederick Harlow was an American psychologist best known for his maternal-separation and social isolation experiments on rhesus monkeys, which demonstrated the importance of care-giving and companionship in social and cognitive development...
studied the effects of maternal and social deprivation
Maternal deprivation
The term maternal deprivation is a catch-phrase summarising the early work of psychiatrist and psychoanalyst, John Bowlby on the effects of separating infants and young children from their mother although the effect of loss of the mother on the developing child had been considered earlier by Freud...
on rhesus monkey infants (a form of environmental stimulus deprivation). This established the importance of social stimulation for normal cognitive
Cognitive development
Cognitive development is a field of study in neuroscience and psychology focusing on a child's development in terms of information processing, conceptual resources, perceptual skill, language learning, and other aspects of brain development and cognitive psychology compared to an adult's point of...
and emotional development.
Synaptogenesis
Rats raised with environmental enrichment have thicker cerebral cortices (3.3-7%) that contain 25% more synapses. This effect of environmental richness upon the brain occurs whether it is experienced immediately following birth, after weaning, or during maturity. When synapse numbers increase in adults, they can remain high in number even when the adults are returned to improvised environment for 30 days suggesting that such increases in synapse numbers are not necessarily temporary. However, the increase in synapse numbers has been observed generally to reduce with maturation. Stimulation affects not only synapses upon pyramidal neurons (the main projecting neurons in the cerebral cortex) but also stellateStellate cell
In neuroscience, stellate cells are neurons with several dendrites radiating from the cell body giving them a star shaped appearance. The three most common stellate cells are the inhibitory interneurons found within the molecular layer of the cerebellum, excitatory spiny stellate interneurons and...
ones (that are usually interneurons). It also can affect neurons outside the brain in the retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
.
Dendrite complexity
Environmental enrichment affects the complexity and length of the dendriteDendrite
Dendrites are the branched projections of a neuron that act to conduct the electrochemical stimulation received from other neural cells to the cell body, or soma, of the neuron from which the dendrites project...
arbors (upon which synapses form). Higher-order dendrite branch complexity is increased in enriched environments, as can the length, in young animals, of distal branches.
Activity and energy consumption
Synapses in animals in enriched environments show evidence of increased synapse activation. Synapses tend to also be much larger. 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%
- The direct apposition area of glial cells with synapses expands by 19%
- The volume of glial cell nuclei for each synapse is higher by 37.5%
- The mean volume of mitochondria per neuron is 20% greater
- The volume of glial cell nuclei for each neuron is 63% higher
- Capillary density is increased.
- Capillaries are wider (4.35 μm compared to 4.15 μm in controls)
- Shorter distance exist between any part of the neuropilNeuropilIn neuroanatomy, a neuropil, which is sometimes referred to as a neuropile, is a region between neuronal cell bodies in the gray matter of the brain and blood-brain barrier . It consists of a dense tangle of axon terminals, dendrites and glial cell processes...
and a capillary (27.6 μm compared to 34.6 μm)
These energy related changes to the neuropil
Neuropil
In neuroanatomy, a neuropil, which is sometimes referred to as a neuropile, is a region between neuronal cell bodies in the gray matter of the brain and blood-brain barrier . It consists of a dense tangle of axon terminals, dendrites and glial cell processes...
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 motor skills. Research upon “acrobatic” skill learning in the rat shows that it leads to increased synapse numbers.Maternal transmission
Environmental enrichment during pregnancyPregnancy
Pregnancy refers to the fertilization and development of one or more offspring, known as a fetus or embryo, in a woman's uterus. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets...
has effects upon the fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
such as accelerating its retinal development.
Neurogenesis
Environmental enrichment can also lead to the formation of neuronsNeurogenesis
Neurogenesis is the process by which neurons are generated from neural stem and progenitor cells. Most active during pre-natal development, neurogenesis is responsible for populating the growing brain with neurons. Recently neurogenesis was shown to continue in several small parts of the brain of...
(at least in rats) and reverses the loss of neurons in the hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...
and memory impairment following chronic stress. However, its relevance has been questioned for the behavioral effects of enriched environments.
Mechanisms
Enriched environments affect the expression of genesGênes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...
in the cerebral cortex and the hippocampus that determine neuronal structure. At the molecular level, this occurs through increased concentrations of the neurotrophins NGF
NGF
NGF may refer to:*Nerve growth factor*Naval gunfire*Northern Group of Forces*National Golf Foundation*North German Federation...
, NT-3, and changes in BDNF. This alters the activation of cholinergic
Cholinergic
The word choline generally refers to the various quaternary ammonium salts containing the N,N,N-trimethylethanolammonium cation. Found in most animal tissues, choline is a primary component of the neurotransmitter acetylcholine and functions with inositol as a basic constituent of lecithin...
neurons, 5-HT, and beta-adrenolin
Adrenergic receptor
The adrenergic receptors are a class of metabotropic G protein-coupled receptors that are targets of the catecholamines, especially noradrenaline and adrenaline ....
. Another effect is to increase proteins such as synaptophysin
Synaptophysin
Synaptophysin also known as the major synaptic vesicle protein p38 is a protein that in humans is encoded by the SYP gene.-Genomics:...
and PSD-95
DLG4
PSD-95 also known as SAP-90 is a protein that in humans is encoded by the DLG4 gene....
in synapses. Changes in Wnt signaling
Wnt signaling pathway
The Wnt signaling pathway is a network of proteins best known for their roles in embryogenesis and cancer, but also involved in normal physiological processes in adult animals.-Discovery:...
have also been found to mimic in adult mice the effects of environmental enrichment upon synapses in the hippocampus. Increase in neurons numbers could be linked to changes in VEGF
Vascular endothelial growth factor
Vascular endothelial growth factor is a signal protein produced by cells that stimulates vasculogenesis and angiogenesis. It is part of the system that restores the oxygen supply to tissues when blood circulation is inadequate....
.
Resilience and rehabilitation
Research (as least upon rats) suggests that environment enrichment might reduce the effects or ameliorate the cognitive impairments caused by a diverse variety of conditions and neurological disorders.- Aging, (also in dogs)
- Alzheimer’s disease
- Huntington's diseaseHuntington's diseaseHuntington's disease, chorea, or disorder , is a neurodegenerative genetic disorder that affects muscle coordination and leads to cognitive decline and dementia. It typically becomes noticeable in middle age. HD is the most common genetic cause of abnormal involuntary writhing movements called chorea...
- Parkinson's diseaseParkinson's diseaseParkinson's disease is a degenerative disorder of the central nervous system...
- StrokeStrokeA stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...
- Chronic spinal cord injuries
- AmblyopiaAmblyopiaAmblyopia, also known as lazy eye, is a disorder of the visual system that is characterized by a vision deficiency in an eye that is otherwise physically normal, or out of proportion to associated structural abnormalities of the eye...
- Rett syndromeRett syndromeRett syndrome is a neurodevelopmental disorder of the grey matter of the brain that almost exclusively affects females. The clinical features include small hands and feet and a deceleration of the rate of head growth . Repetitive hand movements, such as wringing and/or repeatedly putting hands into...
- AutismAutismAutism is a disorder of neural development characterized by impaired social interaction and communication, and by restricted and repetitive behavior. These signs all begin before a child is three years old. Autism affects information processing in the brain by altering how nerve cells and their...
- Prenatal and perinatal cocaine exposure
- Fetal alcohol syndromeFetal alcohol syndromeFetal alcohol syndrome is a pattern of mental and physical defects that can develop in a fetus in association with high levels of alcohol consumption during pregnancy. Current research also implicates other lifestyle choices made by the prospective mother...
- Lead exposureLead poisoningLead poisoning is a medical condition caused by increased levels of the heavy metal lead in the body. Lead interferes with a variety of body processes and is toxic to many organs and tissues including the heart, bones, intestines, kidneys, and reproductive and nervous systems...
- Prenatal and maternal separationMaternal deprivationThe term maternal deprivation is a catch-phrase summarising the early work of psychiatrist and psychoanalyst, John Bowlby on the effects of separating infants and young children from their mother although the effect of loss of the mother on the developing child had been considered earlier by Freud...
stress - Child neglectChild neglectChild neglect is defined as:# "the failure of a person responsible for a child’s care and upbringing to safeguard the child’s emotional and physical health and general well-being"...
- Sensorial deprivation
Humans
Though environmental enrichment research has been mostly done upon rodents, similar effects occur in primates, and are likely to affect the human brain. However, direct research upon human synapses and their numbers is limited since this requires histological study of the brain. A link, however, has been found between educational level and greater dendritic branch complexity following autopsy removal of the brain.Localized cerebral cortex changes
MRI detects localized cerebral cortexCerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
expansion after people learn complex tasks such as mirror reading (in this case in the right occipital cortex), three-ball juggling (bilateral mid-temporal
Temporal lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....
area and left posterior intraparietal sulcus
Intraparietal sulcus
The intraparietal sulcus is located on the lateral surface of the parietal lobe, and consists of an oblique and a horizontal portion. The IPS contains a series of functionally distinct subregions that have been intensively investigated using both single cell neurophysiology in primates and human...
), and when medical students intensively revise for exams (bilaterally in the posterior and lateral parietal cortex). Such changes in gray matter volume can be expected to link to changes in synapse numbers due to the increased numbers of glial cells and the expanded capillary vascularization needed to support their increased energy consumption.
Institutional deprivation
Children that receive impoverished stimulation due to being confined to cots without social interaction or reliable caretakers in low quality orphanages show severe delays in cognitive and social development. 12% of them if adopted after 6 months of age show autistic or mildly autistic traits later at four years of age. Some children in such impoverished orphanages at two and half years of age still fail to produce intelligible words, though a year of foster care enabled such children to catch up in their language in most respects. Catch-up in other cognitive functioning also occurs after adoption, though problems continue in many children if this happens after the age of 6 monthsSuch 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 orbital prefrontal cortex
Orbitofrontal cortex
The orbitofrontal cortex is a prefrontal cortex region in the frontal lobes in the brain which is involved in the cognitive processing of decision-making...
, amygdala
Amygdala
The ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...
, hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...
, temporal cortex, and brain stem
Brain stem
In vertebrate anatomy the brainstem is the posterior part of the brain, adjoining and structurally continuous with the spinal cord. The brain stem provides the main motor and sensory innervation to the face and neck via the cranial nerves...
. They also showed less developed white matter
White matter
White matter is one of the two components of the central nervous system and consists mostly of myelinated axons. White matter tissue of the freshly cut brain appears pinkish white to the naked eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color is due to...
connections between different areas in their cerebral cortices, particularly the uncinate fasciculus
Uncinate fasciculus
The uncinate fasciculus is a white matter tract in the human brain that connects parts of the limbic system such as the hippocampus and amygdala in the temporal lobe with frontal ones such as the orbitofrontal cortex. Its function is unknown though it is affected in several psychiatric conditions...
.
Conversely, enriching the experience of preterm infants
Premature birth
In humans preterm birth refers to the birth of a baby of less than 37 weeks gestational age. The cause for preterm birth is in many situations elusive and unknown; many factors appear to be associated with the development of preterm birth, making the reduction of preterm birth a challenging...
with massage
Massage
Massage is the manipulation of superficial and deeper layers of muscle and connective tissue to enhance function, aid in the healing process, and promote relaxation and well-being. The word comes from the French massage "friction of kneading", or from Arabic massa meaning "to touch, feel or handle"...
quickens the maturating of their electroencephalographic
EEG
EEG commonly refers to electroencephalography, a measurement of the electrical activity of the brain.EEG may also refer to:* Emperor Entertainment Group, a Hong Kong-based entertainment company...
activity and their visual acuity
Visual acuity
Visual acuity is acuteness or clearness of vision, which is dependent on the sharpness of the retinal focus within the eye and the sensitivity of the interpretative faculty of the brain....
. Moreover, as with enrichment in experimental animals, this associates with an increase in IGF-1.
Cognitive reserve and resilience
Another source of evidence for the effect of environment stimulation upon the human brain is cognitive reserveCognitive reserve
The term cognitive reserve describes the mind's resilience to neuropathological damage of the brain. The mind's resilience is evaluated behaviorally, whereas the neuropathological damage is evaluated histologically, although damage may be estimated using blood-based markers and imaging methods...
(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 generally engaging in cognitively demanding activities. The more education a person has received, the less the effects of aging, dementia, white matter hyperintensities, MRI-defined brain infarcts, Alzheimer’s disease, and traumatic brain injury. Also, aging and dementia are less in those that engage in complex cognitive tasks. The cognitive decline of those with epilepsy could also be affected by the level of a person’s education.
See also
- Behavioral enrichment
- Cognitive reserveCognitive reserveThe term cognitive reserve describes the mind's resilience to neuropathological damage of the brain. The mind's resilience is evaluated behaviorally, whereas the neuropathological damage is evaluated histologically, although damage may be estimated using blood-based markers and imaging methods...
- Maternal deprivationMaternal deprivationThe term maternal deprivation is a catch-phrase summarising the early work of psychiatrist and psychoanalyst, John Bowlby on the effects of separating infants and young children from their mother although the effect of loss of the mother on the developing child had been considered earlier by Freud...
- Neural developmentNeural developmentNeural development comprises the processes that generate, shape, and reshape the nervous system, from the earliest stages of embryogenesis to the final years of life. The study of neural development aims to describe the cellular basis of brain development and to address the underlying mechanisms...
- NeuroplasticityNeuroplasticityNeuroplasticity is a non-specific neuroscience term referring to the ability of the brain and nervous system in all species to change structurally and functionally as a result of input from the environment. Plasticity occurs on a variety of levels, ranging from cellular changes involved in...
- Phenotypic plasticityPhenotypic plasticityPhenotypic plasticity is the ability of an organism to change its phenotype in response to changes in the environment. Such plasticity in some cases expresses as several highly morphologically distinct results; in other cases, a continuous norm of reaction describes the functional interrelationship...
- Rat ParkRat ParkRat Park was a study into drug addiction conducted in the late 1970s , by Canadian psychologist Bruce K. Alexander and his colleagues at Simon Fraser University in British Columbia, Canada....
- StimulationStimulationStimulation is the action of various agents on nerves, muscles, or a sensory end organ, by which activity is evoked; especially, the nervous impulse produced by various agents on nerves, or a sensory end organ, by which the part connected with the nerve is thrown into a state of activity.The word...
- SynaptogenesisSynaptogenesisSynaptogenesis is the formation of synapses. Although it occurs throughout a healthy person's lifespan, an explosion of synapse formation occurs during early brain development...