Introduction to Environment and Physiology

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Discuss two effects of the environment on physiological processes.

Environment Effect #1: Deprivation and enrichment and their effects on neuroplasticity (How our environment can impact our brain’s development)

Environmental Effect #2: Levels of light and it’s influence on melatonin levels and the development of S.A.D. (As well as rapid air travel across time zones and its effect on melatonin levels and circadian rhythms.)

Enrichment/Deprivation and Neuroplasticity:

Rosenzweig conducted a laboratory experiment on rats to investigate whether or not our environmental conditions can influence brain development. His results can be seen in the further information handout below. Another important study is Perry’s research on neglected 3 year olds and healthy 3 year old humans (this study is in the revision textbook). This study supported the results of the animal study, showing that sensory deprivation can be detrimental to the development of the cerebral cortex and other areas of the brain.

Watch this episode of: ‘Our Universe Within’ Ep 3 from 3mins -18:49 and from 27.50 – 30:20secs to learn how neurons rebuild connections after damage. If you are interested in the brain, all four episodes of ‘Our Universe Within’ are available on youtube. You should be able to gather information from this video based on how our environment can influence our physiology (in this case the physiology is neuroplasticity).


Rapid Air Travel and Circadian Rhythms (Melatonin)

Our bodies have set circardian rhythms (body clocks) based on light cycles of the day (see the sheet below for an image that shows how our body changes throughout the day). One of these important changes is the release and suppression of the hormone melatonin. This hormone is released based on levels of light in the environment. When we travel across time zones, we end up in environments where the light changes at times we are not used to. This disrupts the levels of melatonin in the body, which can have an effect on our behaviour. This is known as jet lag, and has various symptoms such as headaches, nausea and sleep disruptions.

Environment Physiology Flowchart


Rosenzweig’s Rat Experiment

For more information on this study, see the blue textbook (pg 46-7), Myers’ textbook (pg 118) and the revision textbook (pg 10).

Background Info

For a long time it was widely believed that our brain’s growth happened at a fixed rate. Many people thought that by the time we were about 4 – 6 years old, our brains had stopped developing and we were either going to be smart, dumb or average and that this wouldn’t change in our lives. However, research studies have demonstrated our brain’s impressive ability to grow and adapt throughout our lives as a result of stimulation. During the process of learning something new, our neurons undergo a process called dendritic branching. This is when the dendrites of neurons make new connections to other neurons. It is these connections that enable us to learn and master new skills. After learning about H.M. you will also know that each area of the brain has a particular function. This is known as localization of brain function. However, this isn’t fixed and can change. People can lose parts of their brain and due to dendritic branching and the establishment of new neural connections they can shift the function to a new part of the brain. This is called neuroplasticity. Even more impressive is the fact that the brain is capable of growing new neurons, which is called neurogenesis. It was believed for a long time that this wasn’t possible. So what are the factors that can cause our brain to grow and develop in new ways? This was the area of research for Mark Rosenzweig and his colleagues.

The Environments Influence on the Brain (Rosenzweig)

To investigate the effects of the environment on brain growth and development (neuroplasticity), Rosenzweig and his colleagues designed an experiment where rats were placed in different cages and lived for 30-60 days before they were euthanized and a post-mortem study was conducted to measure the thickness and heaviness of the brain cortex as well as the amount of acetylcholine receptors and synapses.

In Rosenzweig’s rat experiment, male rats were chosen from different litters to be randomly allocated to two different conditions: enriched condition (EC), and the deprived condition (DC). In the EC, there were about 10-12 rats and there were a range of toys that the rats could play with. This group also received “maze training”. The DC was a cage that was slightly smaller and the rat was alone and the cage was isolated in a separate room from the other cages. Both conditions had adequate food and water. The rats lived in these different conditions for four to ten week periods (30-60 days). After these treatment periods, the rats were autopsied in order to determine if any differences had developed. The scientist doing the autopsy did not know which cages the rats had been in. The rat’s brains were dissected and various sections were measured, weighed and analyzed to determine the amount of cell growth and levels of neurotransmitter activity.

Rosenzweig found that rats living in the EC developed a heavier and thicker brain cortex. More specifically, the frontal lobes of the rats were heavier and they had developed more acetylcholine receptors. Further studies found that the brain weight of the rats can increase 7 – 10% and synapses increase by about 20%. The results were quite groundbreaking at the time and Rosenzweig was so surprised by the results that he replicated the research numerous times. With each replication the same results were obtained.

Follow up experiments even investigated if researchers could determine which rats had lived in which cages based on watching videos of the rats. Depending on their curiosity and activity, the researchers could determine the enriched and deprived rats.

While this study has been performed on rats, can we make conclusions regarding enrichment and stimulation and the human brain? One study shows that pre-mature babies (of both rats and humans) put on weight more quickly and develop more neurologically (i.e. their brain develops) more when they are handled (e.g. touched and cuddled) and when they are not. Perry also performed MRI scans of 3 year old children who had been extremely neglected and those who had not. The MRI scans reveal that the neglected children had smaller brains than the “normal” children.

Rosenzweig’s experiments have had a significant impact on psychology as they clearly show that there is a cause and effect between the environment and brain development. The work by Rosenzweig and Bennet served as a catalyst for continued research in this area.

Critical Thinking Questions

  • How did Rosenzweig control for possible confounding variables?
  • What are the ethical considerations involved in this experiment?
  • Are the results reliable and/or valid? Why/why not?
  • What are the strengths and limitations of these studies?
  • What type of experiment was Perry’s?
  • How can this knowledge be applied to everyday life and society?

This video shows how Rosenzweig’s study has provoked research in to other fields. It raises interesting questions like how we should approach the punishment and rehabilitation of criminals. After all, if the environment can affect the brain, and studies show that criminal’s have differences in their brain structure (smaller amygdalas), shouldn’t we be providing them with more stimulating environments to increase their brain growth, instead of tiny cells?


Jetlag and Melatonin 

The information that you learned about melatonin and it’s role in SAD (check the page on hormones) can be applied to this question. The below information will help you understand jetlag and its link to melatonin levels.

Jet lag and Melatonin

Jet lag is a physiological condition which results from alterations to the body’s circadian rhythms; it is classified as one of the circadian rhythm sleep disorders. Jet lag results from rapid long-distance transmeridian (east–west or west–east) travel, as on a jet plane. The condition of jet lag may last several days, and a recovery rate of one day per time zone crossed is a fair guideline.


Jet lag is a chronobiological-related problem, similar to issues often induced by shift work. When traveling across a number of time zones, the body clock will be out of synchronization with the destination time, as it experiences daylight and darkness contrary to the rhythms to which it has grown accustomed: the body’s natural pattern is upset, as the rhythms that dictate times for eating, sleeping, hormone regulation and body temperature variations no longer correspond to the environment nor to each other in some cases. To the degree that the body cannot immediately realign these rhythms, it is jet lagged.

The condition is not linked to the length of flight, but to the transmeridian (west–east) distance traveled. A ten-hour flight from Europe to southern Africa does not cause jet lag, as travel is primarily north–south.


The symptoms of jet lag can be quite varied, depending on the amount of time zone alteration, time of day and individual differences. They may include the following:

Direction of travel

There seems to be some evidence that for most people, traveling west to east is more disruptive. This may be because most people have a circadian period which is a bit longer than 24 hours, making it easier to stay up later than to get up earlier.


Melatonin is present in the bloodstream naturally in differing amounts according to the time of day. It is produced by the pineal gland in darkness; secretion stops when there is light to the eyes. It plays a key role in the circadian rhythm which regulates various significant body functions.

A 2005 study showed that melatonin was effective in helping people fall asleep at doses of 0.3 milligrams (mg). Then, to treat the jet lag, the recommended dose of melatonin is 0.3–0.5 mg, to be taken the first day of traveling. Administration of higher doses can cause sleepiness, lethargy, confusion, and decreased mental sharpness.


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