Enrichment & Behavior
What's the study all about?
Enrichment has the potential to create larger masses of cortical tissue and increase learning ability. In this study, the effect of enrichment on maze learning was investigated. Two groups of rats were in either an enriched environment or a barren environment. Each performed in maze runs and the time spent in the maze as well as the number of mistakes was recorded for each individual. Those in an enriched environment showed significantly better performances than rats that were not enriched, supporting previous similar studies.
An introduction to enrichment studies...
The
rat has been a permanent fixture in biological laboratories around the
world for over 150 years. They take part in everything from biomedical
and genetic research to chemical and household product testing to developmental,
neurological, physiological, and psychological analysis. Millions of lab
animals undergo experimentation each year and all too often, no part of
their natural environment or stimulation is provided for them. Most experiments
are designed on the basis of economic and ergonomic features, with little
consideration for animal welfare. Possibly more pertinent is that lab
housing conditions can affect an animals’ normal behavior, which
is a major observed product of nearly all experimental designs. Abnormal
behavior, including locomotor activity from the lack of stimulation, could
then be taken as a result rather of some experimental variable. It’s
important that animals have a certain degree of control over their environment
to reduce stress. Environment indeed plays a role in such aspects as body
weight, heart rate, hormonal levels, immune status, and reproductive function.
So, the implications of the use of a more natural or stimulating environment
within the lab are apparent. But, how does abnormal behavior, or behavior
at all relate directly to the environment and what effect does it have
on learning, another extensively studied area that uses the rat model?
Abnormal patterns of behavior are those that do not occur in the wild. These patterns are seen most often as an adaptation to barren environments. There is an overall decrease in interaction with the environment shown, for example, by lying down and sleeping more often, over-reaction to novel or unexpected events with fearful or aggressive responses, and the development of stereotypical behaviors like pacing or bar biting. Sometimes, abnormal patterns will even lead to compulsive self-mutilation. Behavior is flexible and rats are capable of dealing with and adapting to their environment, as they need to. However, in long-term captivity, animal behavior gradually loses its flexible nature. And self-directed behaviors show the animal closing off the environment rather than interacting with it. Attention and learning abilities of animals in prolonged captivity may gradually become impaired. Environmental enrichment is the provision of stimuli, which promotes the expression of species-appropriate behavioral and mental activities. Enrichment then reduces these undesirable effects of captivity on animals.
A basic understanding of learning and memory is also important to understanding the environmental role on the rat’s behaviors. Learning is the acquisition of new information, and memory is the retention and retrieval of learned information. While anatomical connections between neurons are set by genetics, the strength and effectiveness of synapses are not predetermined and can be altered by experience.
Perhaps the most interesting of studies are
the effects of environment and enrichment on the brain, specifically the
cortex and its effect on learning. Although enriched environments do not
alter the number of nerve cells, the size of preexisting ones in the cerebral
cortex increases. It is equally important to stress that an impoverished
environment will diminish nerve cells, just as cortical tissue will increase
with stimulation. Structural differences can be detected in cortices of
animals at any age based on their levels of stimulation in the environment.
Dendrite growth and cortex thickness are exhibited in the very young and
even in the very old. Beneficial effects of enrichment like improved maze
behavior has been observed previously in rats. What does this mean, though?
The idea is that learning in animals that receive enrichment in all forms of their physical environment, social environment, and diet will be improved when compared to their nonenriched counterparts. Those animals that receive enrichment potentially have larger cortices with enlarged nerve cells, which with numerous glial support cells are utilized by the rat to solve maze problems more effectively. Visual systems are influenced and improved by a stimulating environment, which also has an impact on maze learning. Animals from impoverished environments show fewer tendencies to manipulate novel objects and investigation is decreased in them as well. Again, this would have an impact on maze learning. Maze learning is associated with the ability to learn the locations of key features in the environment and is a direct reflection of an animal’s evolved response to special challenges associated with their own environment. The idea of this experiment was to use this information to test the learning ability of enriched and nonenriched rats of varying ages with the assumption that those in the stimulating environment would be more successful. The implications of this both inside the laboratory setting and in the human social world must not be overlooked.
Materials and methods...
Maze
construction. The maze was constructed using builder’s grade
luan wood. The layout featured 4-inch pathways and openings throughout
and was constructed in two pieces for ease of transport. Wood barriers
were attached with hot glue and reinforced where necessary with duct tape.
The duct tape was also used on the top of all the barriers to reduce splintering
of the wood. The top was made from mesh and was affixed with Velcro, however
ideally, the top should be made from plexiglass drilled with air holes.
The designated start and finish marks for these trials are indicated in
the figures to the right.
Subjects and conditions. For the group not receiving enrichment, four Long-Evans rats bred in the lab were used. They were housed together in a clear plastic container similar to that seen below left. They received Harlan Teklad lab block diet for rats and had open access to water. They were also under controlled lighting conditions with 14 hours light and 10 hours dark. Handling was kept minimal throughout the experimental process for this group and no enrichment items were offered outside of maze completion rewards. Additionally, the substrate for the cage was Carefresh recycled paper bedding. For the enrichment group, four rats bred in ratteries were used. The subjects were a 2-month old, a 4.5-month old, a 7-month old, and a 2.25-year old. Their housing can be seen by clicking here and was, as shown, highly enriched. Diet was also enriched, consisting of a variety of grains, legumes, vegetables, fruits, cereals, lean meats, dairy products, and moderate amounts of sugary treats. Access to water was always available. No artificial lighting conditions were created for this group and routine, extensive handling occurred daily. The bedding in this group’s cage was also Carefresh, however the environment also contained several enrichment items from hidden foods to wooden bird toys to bells, a running wheel, squeaky toys, and crinkle balls.
Trials. Maze runs were conducted
over a 30-day period for both groups. The sessions were run 5 days in
a row, followed by 2 days off, and so on, ending in 1 final trial. Times
were recorded in the maze from start to finish for each individual rat,
as were incorrect number of channel moves. Channels were considered incorrect
if they resulted in a dead end. Upon completion of the maze, each rat
received a treat. The treats offered were popcorn, crackers, cookies,
or Vitacraft yogurts to allow a variety for the individual. The treat
was always smeared with Nutrical, a nutritious, highly palatable vitamin
supplement with a strong odor. Data was compiled for all the trials when
completed.
The results...
This data obtained offers
one major conclusion. The hypothesis that enriched environments enable rats
to perform better in learning experiments such as the maze is an accurate
statement based on these results. In considering both the total time spent
in the maze and the number of mistakes made, the enriched group was far
more successful. A graphical representation of these performances can be
seen below. In reference to the results obtained from each rat’s time
spent in the maze, there is a
significant increase in overall times for
the nonenriched rats. Although times decreased for all rats over the trial
period, there was no sure indication that the nonenriched rats were learning
the maze pattern. Their times did decrease, but this is believed to be due
mainly to the speed in which they moved through the maze as they became
more comfortable with the new surroundings, rather than their familiarity
with the paths. However, with the enriched rats, a gradual decrease in time
was seen to the point where the time spent in the maze was just enough to
get from start to finish. The data obtained for mistakes made in the maze
further supports this concept. The enriched group showed a steady, consistent
decrease in mistakes over the trial period. In contrast, the nonenriched
rats made only some improvement, and at no point did the number of mistakes
decline in such a way to be associated with learning. Even in the final
trials, there was no real improvement, and the number of mistakes remained
relatively the same even though time in the maze decreased. These results
were as expected.
There were also behavioral results associated with the presence or absence of enrichment in the groups, which are believed to be a part of their learning ability. The enriched group was handled and encountered novel stimulation or environments daily. This enhances the active character of behavior, resulting in an increasing frequency of interactive behaviors like exploration, manipulation, and play. They are better able to cope with new and unexpected changes and are less likely to become stressed. So, when this group first encountered the maze, they were curious, did not appear to be under stress, and moved through the maze easily. However, the nonenriched group, having not been handled or placed in new environments, displayed signs of stress like urination and defecation in the maze and crouching in corners. This behavior is consistent with a laboratory animal that previously had no outside sources of enrichment. A decline in exploration is normally seen in these animals and was indeed encountered in this experiment. This must be considered in the results as it plays a significant role in learning ability. The enriched environment not only affects the brain in learning; it affects the way in which each individual perceives and interacts with the environment. Previous studies that measured cortex size in relation to enrichment and maze learning found that there are widespread changes in the brain of enriched rats. Enrichment involving all five senses produces changes that are correlated with not only maze learning, but also interaction with any new sensory condition. Healthy support systems, like the cardiovascular, respiratory, urinary, and digestive systems are also essential for a healthy brain. These are maintained with a varied, enriched diet and exercise. Also involved is the limbic system, hippocampus, and hypothalamus. These areas, when stimulated with mental challenges and social interaction, also produce changes that affect learning and environment interactions. These things are all considered in the outcome of an experiment such as this.
The overall results from this experiment support previous studies. Enrichment does affect the rat’s ability within a maze positively. This study did not include the study of the neurological aspect of this statement, but uses previous results as an understanding of why this expected outcome occurs. Another look at the averages of the times and mistakes in the maze makes even clearer the striking difference between the groups.
What it all means...
The results of this experiment
maintain previous experimental results. Enrichment does improve learning
in rats. The implications of this in the laboratory setting alone are
great. Many scientists are reluctant to enrich lab cages. They dread the
increase in behavioral variability will ruin consistent experimental results.
However, as control increases for the researcher, it decreases for the
animal. An animal will actually become a more ‘normal’ model
for investigation if enriched. Responses to experimental situations would
actually be more stable and consistent and the number of animals needed
could also be decreased. It has been proposed before that not only can
environmental enrichment enhance the well-being of animals, but it may
also improve the quality of animal management and research. Groups of
animals may also be better maintained. In groups, barbering and aggressive
behavior in mice was reduced 60% just by offering enrichment. Enrichment
need not be extravagant. It just needs to provide a living environment
for captive animals to express natural behaviors. Social stimuli like
other animals and human interaction are important. The physical environment
should include items for resting, gnawing, exploring, and hiding. A variety
of foods should be offered, sometimes hidden in the bedding to satisfy
the natural foraging behaviors of many animals. Even sensory enrichment
is important. Having a radio playing can mask sudden noises. Light intensity
should be lowered as it may have effects on eyes of rodents, especially
albinos, whose retinas are sensitive. Shelters should also be provided.
Any or all of these are relatively easy to provide and will offer a more
pleasing environment for the lab animal, as well as a more pleasant lab
animal to work with.
to develop the whole cortical mantle and play experience aides the development
of cognitive, social, emotional, and physical functioning. Baylor College
of Medicine reported in 1997 that children lacking an enriched environment
develop 20 – 30% smaller brains than normal for their age. This
brain stimulation is critical to the growth of neural synapses, the hardwiring
of the brain’s circuits. So, not only in the lab is enrichment important.
Its effects can be seen in humans as well. There are even studies that
now look at the human elderly brain. There is now great optimism for the
use of enrichment over inactivity in the aging brain to slow the effects
of brain disorders. Maintaining curiosity and enrichment throughout a
lifetime seems to result in a stronger capacity for experiencing the environment
and for learning.