How the Environment Affects the Brain
Brain plasticity and the impact of an enriched environment on brain physiology
 The brain is a dynamic system that interacts with the environment
 The brain is physically sculpted by experience
 The brain can determine and change behavior
 Behavior and environment can change the brain
Framework
Vocabulary list
Enriched: added greater value or significance to
Plasticity: the capability of being molded, shaped, or formed
Brain plasticity: the brain's ability to rearrange the connections between its neurons –
changes that occur in the structure of the brain as a result of learning or experience
Dendritic branching: when the dendrites of neurons grow in numbers and connect with
other neurons to create a new trace in the brain, whenever we learn something new
Nervous system: the system of nerves and nerve centers in an animal or human,
including the brain, spinal cord, nerves, and ganglia
Central nervous system: the part of the nervous system comprising the brain and spinal
cord
Hubel and Wiesel (1965)
 Demonstrated that the brain could change as a response to environmental input
 The experiment was done with rats but it can be generally accepted that
environmental enrichment can modify the brain, especially the cerebral cortex,
which is the area of higher cognitive functioning
 The brain is constantly changing as a result of experience throughout the lifespan
Rosenzweig and Benett (1972)
Aim: In the belief that animals raised in highly stimulating environments will
demonstrate differences in brain growth and chemistry when compared with animals
reared in dull circumstances, the experiment was carried out to measure the effect of
either enrichment or deprivation to the development of neurons in the cerebral cortex
Procedure: The researchers randomly assigned 12 sets of three male rats (each set from
the same liter) into one of three circumstances – remaining in the laboratory cage with
the rest of the colony, an enriched environment cage and a deprived cage. 12 male rats
in each circumstance spent 4 to 10 weeks in their respective environments
 The standard laboratory colony cage contained several rats in an adequate space
with food and water always available
 The enriched, stimulating environment was virtually a rat’s Disneyland where 6-8
rats lived in a “large cage furnished with a variety of objects with which they
could play”
 The deprived environment was a slightly smaller cage isolated in a separate
room in which the rat was placed alone with adequate food and water
The rats were then sacrificed so that autopsies could be carried out on their brains to
determine if any differences had developed between the brains of the enriched rats
versus the deprived rats. The examinations were done in random order by code number.
The rats’ brains were dissected and the various sections were measured, weighed, and
analyzed to determine amount of cell growth and levels of neurotransmitter activity.
Findings: The brains of the enriched rats were different from the deprived rats in many
ways. Although the differences are not large, Rosenzweig et al. are confident that they
are genuine. The same patterns of differences are found when the experiments are
replicated. The most consistent effect of experiment was the ratio of the weight of the
cortex to the weight of the rest of the brain (the sub-cortex).
 The cerebral cortex (responds to experience and is responsible for movement,
memory, learning, and all sensory input) of the enriched rats was significantly
heavier and thicker.
 There was greater activity of the nervous system enzyme acetylcholinesterase
found in the brain tissue of the enriched rats.
 Cortical thickness increases even further if the rats are placed with other rats.
The combination of having company and many interesting toys created the best
conditions for developing cerebral thickness.
 There were no significant differences found between the two groups of rats in
the number of brain cells (neurons) but the enriched rats produced larger
neurons.
 The ratio of RNA to DNA (the two most important brain chemicals for cell growth)
was greater for the enriched rats (higher level of chemical activity in the
enriched rats’ brains).
 The synapses of the enriched rats’ brains were 50% larger than those of the
deprived rats.
Conclusions: Many aspects of brain anatomy and brain chemistry are changed by
experience. The cortex increases in weight quite readily in response to experience
whereas the rest of the brain changes little.
Strengths: The examinations were done in random order by code number so that the
person doing the autopsy would not know in which condition the rat was raised, the
ratios between the weight of the cortex to the weight of the rest of the brain was
considered cancelling out individual differences
Limitations: Ecological validity: humans are not rats, therefore, the study can only be
generalized to humans only to some extent.
Significance of study in terms of how it explains aspects of human behaviour: Brains
are physically sculpted by experience. Aspects of the brain can be changed as we go
through experiences. As a person develops a greater number of skills and abilities, the
brain actually becomes more complex and heavier. People who were unable to have
certain experiences, will have that part of their brain be significantly less developed, less
convoluted, and thinner in comparison to those who have had those experiences. As
long as that specific part of the brain is being used, no matter how old the person is, it
isn’t lost. If learning always results in an increase of dendritic branchings, then the
findings from animal studies which show brain plasticity in response to environmental
stimulation are important for the human cortex as well.
Schore et al. (1996)
 Applied Rosenzweig’s notions of environmental influences on brain development
to mental illness in humans
 When the emotional attachment of the infant to the caregiver is stressful and
unsatisfying, the hormones created in the infant’s nervous system cause the
abnormal development of specific structures and emotional circuits in the cortex
 Abnormal brain developments triggered by negative environmental factors
during infancy create and enduring increased susceptibility to various
psychological disorders later in life
Post et al. (1996)
 Echos Schore’s findings and goes a step further to suggest that stress and early
episodes of psychological disorders such as depression or bipolar mental illness
may actually leave biochemical residues in the central nervous system in relation
to their patterning, severity, and recurrence.
 An inherited tendency toward mental illness may create early abnormal
psychological episodes that cause physical changes in the nervous system,
leading to ongoing mental illness later in and throughout life
 Early interventions may be more important than previously thought in
preventing mental illnesses in adulthood