2.5 Discuss two effects of the environment on physiological processes

2.5 Discuss two effects of the environment on physiological processes

Effect 1: Environmental effects on dendritic branching (brain plasticity)

Environmental stimulation refers to the way the environment provides stimulation in the form of social interaction and learning opportunities for animals and humans.Experiences are processed in the brain’s nervous system, and stimulating environments will it result in increased numbers of synapses (brain plasticity). Gopnick et al. (1999) describe neurons as growing telephone wires that communicate with each other. An enriched environment is characterized by multiple opportunities to learn new things.  researchers have used animal models to study synaptic changes in the brain because it is not possible to use humans and deprivation experiments. Instead researchers use case studies of children who have grown up in total neglect, i.e. with little or no experience of language, touch and interactions with other humans. The brains of neglected children are off the smaller and they were scientific evidence of altered brain function (e.g. in intelligence and emotions).

Rosenzweig, Bennett and Diamond (1972)

Aim: to investigate whether environmental factors such as a rich or impoverished environment affect development of neurons in the cerebral cortex.

Procedure: Transfer place in either an enriched environment (EC) or an impoverished condition (IC).

EC: 10-12 rats in a cage provided with different stimulus objects to explore and play with. This group also received maze training.

IC: Each rat in an individual cage (isolation and no stimulation).

The Rams typically spent 30 to 60 days in their respective environments before they were killed so that researchers could study the changes in brain anatomy.

Results: the anatomy of the brain was different for rats in the EC and the IC. The brains of EC rats had  increased thickness and higher weight of the cortex. EC rats had developed more acetylcholine receptors in the cerebral cortex (important neurotransmitter in learning and memory).

Evaluation: The experiment was a rigorously controlled laboratory experiment so it was possible to establish cause-and-effect relationship. The experiment used animal models and therefore it may be difficult to generalize to humans unless research with humans provides the same results. Follow-up of this research indicated that just 2 hours a day in an enriched environment produced the same plastic changes in the brain as in rats that had been constantly in the EC condition. This shows that the brain can change and adapt to new situations. Since brain plasticity is assumed to follow the same pattern in animals and humans the implications of the study are that the human brain will also be affected by environmental factors such as intellectual and social stimulation. The research challenged the belief that brain we cannot change. This was an important finding. There are ethical issues in the use of animals in research like this. Since the results contributed to a much better understanding of the role of environmental factors in brain plasticity it can be argued that the research was justified in spite of the ethical issues.

Effect 2: environmental stressors and hippocampal damage in PTSD patients

A stressor is any the event that threatens to disrupt the body's normal balance and starts a stress response such as secretion of stress hormones and activations of the ‘fear sensor’ in the brain, the amygdala. A stressor might be an acute stressor (e.g. being assaulted, having an accident) Or it could be a chronic stressor (e.g. anticipation of violence or worrying). The fight or flight response (coping mechanism) is a pattern of physiological responses that prepares the body to deal with emergency. Sapolsky (1996) has shown in animal studies that long-term stress and prolonged flow of cortisol can influence the size of the hippocampus, which plays a major role in memory.

Trauma and PTSD

Traumatic episodes (i.e. frightening situations from which a person cannot escape) produces intense fear. In about 5% of the population this may lead to PTSD (post-traumatic stress disorder) with effects that can last for a brief period or a lifetime. Combat veterans or survivors of childhood sexual abuse who suffer from PTSD tend to have a number of stress-related problems such as forgetfulness and difficulty learning. In such patients stress-related physiological changes have been observed in the brain, especially in the hippocampus which plays an important role in integrating different aspects of a memory at the time of recollection.

Bremner et al. (2003)

Aim:  to measure the volume of the hippocampus based on the theory that prolonged stress may reduce the volume of the hippocampus due to increased cortisol levels.

Procedure:  MRI scans were made of the brains of the participants and participants completed memory tests (e.g. remembering a story or list of words). Participants were veterans or female adults who had experienced early childhood sexual abuse. Some had developed PTSD, but not all.

Results:  the researchers found that there were deficits in short-term memory and then performed MRI scans of the participants’ brain. They found that the hippocampus was smaller in PTSD patients than in the control group. The veterans with most memory problems also had the smallest hippocampus. The findings showed the clear correlation between number of years of abuse as measured by a trauma test, memory problems and hippocampal volume. People suffering from PTSD often suffer from other psychological disorders (e.g. depression) which could perhaps also play a role in the observed changes in the brain.

Evaluation: The sample was very small so it was difficult to say anything definitive about the relationship between trauma and  hippocampal volume. There could be alternative explanations to differences in hippocampal volume (e.g. that people who suffer from PTSD often suffer from depression as well). Depression is also associated with reduction of the  hippocampus. However, the findings of a large reduction of hippocampal volume in combat-related PTSD has been replicated many times.