An inquiry on the effect of environmental stimuli and stressors on physiological processes and how the brain can adapt to different situations because of its nature of being plastic

By Sanjana Jobalia

Several studies have been conducted in the history of Psychology to observe how a change in environmental stimulus can affect an individual in the biological level of analysis and how the brain can adapt in different situations to attempt to find out how individuals vary. Some studies such as the Maguire et al (2000), Rosenzweig et al (1972), Cohen et al (1993) and Kiecolt and Glaser et al (1995) were conducted to attempt to discover a direct relationship between a particular environmental stimulus and a biological process and others such as Cameron’s case and the case of H.M (1957) talk mainly about brain plasticity.

The brain is a vital organ in our body and needs support from the environment in order to develop. The principles of the biological levels of analysis state that emotions and behaviour can be a product of the anatomy and physiology of the nervous and endocrine system. This suggests that the brain can affect the personality and development of an individual. However, the main aim of this research is to see how the environment can influence or affect the plasticity of the brain. Neurones in the brain pass electrical messages and form connections as a result of dendrite branching when the body is exposed to a certain stimuli. This increases the density of the brain.

An early experiment conducted based on this finding was that of Rosenzweig et al (1972) also known as the rats study. Baby rats were placed in one of the three conditions: impoverished environment- with each rat isolated in a cage with no stimulation ; enriched environment- where each rat was placed in a cage with twelve other rats and stimulation; control environment- with three rats placed without any stimulation. During the duration of 30-60 days, the rats were closely monitored and were then euthanized and scans of their brain were made. The results indicated that rats in an enriched environment on an average had 25% more brain density and mass than those in an impoverished environment and had a greater amount of acetylcholine. Although this experiment was criticised on the basis of ethics, it provided a direct relationship between enhanced stimulus and development and thus opened avenues for studies on humans.


A more recent study is the Maguire et al (2000) which aimed at finding a direct relationship between the amount of time spent receiving a particular stimulus and the amount of grey matter in the brain. 16 male, right-handed participants who were taxi drivers were scanned as well as 16 matched individuals who did not drive a taxi. It was observed that since taxi drivers have to go through two years of rigorous training to learn the roads, their posterior hippocampus was much greater than the posterior hippocampus of non-taxi drivers and that there was a direct correlation between the numbers of years each taxi driver had spent working and the amount of grey matter in the brain. This suggested that a repeated activity could also make neural connections. This study lacked ecological validity because the sample was extremely biased but effectively created a hypothesis that le Chatelier’s principle could be used to define modern psychology.

In order to study the effect of environmental stress on the ability to recover from diseases (cold virus) which indicates immunity, Cohen et al (1995) used a sample of 394 participants who he divided into two groups: the experimental group- which received a dose of a cold virus; and a control group- which received a placebo saline solution. He also made the participants fill out a survey to interpret how much stress is in their lives. 82% of the sample was infected. The recovery period was observed for the next two months. The results suggested that individuals with less stress took the least time to recover and vice a versa. Although harm was caused to the participants, Cohen stated that the scientific benefit of being able to find a correlation between stress and immunity was greater than the cost.

Keicolt-Glaser (1995) set out to find a cause-effect relationship between stresses and recovery time of a wound. 16 carers were matched according to age and income with 16 non-carers. Each individual was given a punch biopsy and were observed during recovery to find that on an average, carers took 24% longer to heal than non-carers. Carers had also reported that they had more stress in their lives. This study and along with all the other studies showed that the environment can affect the body in different ways and aided medical researchers to try to use this information to treat patients. However, in doing this, new findings were uncovered.
Henry Molaisor or H.M was a boy who fell off his bike at age 9, started getting seizures at age 10 and continued getting them till age 27 when he had to get a bilateral medial temporal lobectomy. Although the initial results of this operation were good- no seizures and procedural memory was intact, eventually it became evident to doctors that H.M had developed retrograde and anterograde amnesia as he could not remember anything two years prior to his operation and was unable to make new memories. H.M’s operation was performed in 1953 when information about the brain and its plasticity was not available.

However, Cameron ‘s case was handled very differently. Suffering from similar symptoms from the age of three, Cameron’s doctors suggested to perform a hemispherectomy . With the entire right hand side of her brain gone, Cameron was immediately given stimuli in the form of exercises and brain games to heal her now paralysed left body. Within four weeks, Cameron was able to walk out of the hospital. MRI scans showed that she was building up grey matter and that the left hand side of the brain was taking over the functions of the right hand side. Now, Cameron is completely normal and is rid of her seizures.

Studies of cases like these suggest that the information that has been collected on brain plasticity has the potential to save the lives of hundreds of patients suffering from various physiological ailments. If environmental stimulus can be provided, the brain has the ability to compensate for the shortcomings of biology. However, with the further research of studies like Hubel and Wiesel (196) and the Genie case, it is theorised that different physiological processes have different critical periods in which the brain can be plastic. This can lead to the belief that H.M was beyond the critical period in which his brain could be plastic in the function of memory but Cameron still had enough time. Still, the revelation of the brain and its special functions has had tremendous impact on society and the evolution of Psychology.


About the Author

Sanjana Jobalia

Sanjana Jobalia is an 11th grade student studying in the JNIS IB section. Previously, Sanjana studied IGCSE and topped her school in her board exams. She is currently studying psychology and is very interested in the subject.