The effect of stress on performance is often illustrated by the Yerkes-Dodson law of optimum arousal (Yerkes, & Dodson, 1908). When the body is optimally aroused, mental and physical functioning, such as muscle strength, memory and attention are improved. Conversely, if the arousal level goes beyond certain threshold levels performance levels become worse. Optimum arousal levels are variable depending on the difficulty of the task, the type of task, skill and individual differences. For instance, intellectual tasks require lower levels of arousal than physical tasks, and a more skilled person can withstand more pressure than a less skilled person. The Yerkes-Dodson law can also explain why you may have a writer’s block, procrastinate or fail to retrieve important facts during exams. The reason is that the task is stressing you too much, causing adverse effects on your mental functioning.
How exactly do stressors affect physiological processes? Walter Cannon first investigated the acute stress response, also called the fight-or-flight response in 1929. It is called the fight-or-flight response because it primes animals to fight or flee a threat. The fight-or-flight response starts when a novel stimulus, such as an elevated sound, is relayed from the sensory cortex of the brain via the thalamus through the limbic system to the brain stem. In an instant, the hippocampus and amygdala in the limbic system will appraise whether the perceived stimulus is a threat. If the stimulus is perceived as a threat, the hypothalamus will activate the sympathetic nervous system and the adrenal cortex. The pituitary gland will secrete the hormone ACTH that will travel through the bloodstream and activate the adrenal cortex, which in turn will release approximately 30 hormones that prepare the body for a threat. Afferent nerves from the hypothalamus will also activate the locus coeruleus in the brain stem, which in turn will increase the activity or norepinephrine, making the organism more alert and attentive. If the stimulus is perceived as a threat the locus coeruleus will increase the activation of the sympathetic nervous system. The activation of the sympathetic nervous system through the release of epinephrine and norepinephrine prepare for violent muscular action, which can lead to behavior such as accelerated heart beat and breathing, flushing or paling, inhibition of digestion, liberation of nutrients for muscular action, dilation of pupils, relaxation of the bladder, inhibition of erection, loss of hearing, tunnel vision, better reflex and shaking. (As cited by Smith, Nolen-Hoeksema, Fredrickson, & Loftus, 2003, p. 502ff)
The continuous secretion of stress hormones will lead to associative functional adjustments in the body. One such stress hormone is cortisol, whose main function is to increase blood sugar, aid in metabolism and to suppress the immune system. The amount of cortisol in the blood varies during the day, with the highest levels in the morning and the lowest levels in the afternoon and during sleep (Gorman, 2007). As a high level of cortisol is related to depression and burn-out, this may explain why it is especially difficult to get up in the morning when you are depressed. Anorexia nervosa, caffeine intake and sleep deprivation are all related to increased cortisol levels. Cortisol cooperates with epinephrine to create memories, but long term exposure to cortisol can damage cells in the hippocampus and impair learning. In addition, cortisol is related to appetite and may also shut down the reproductive system. Long term stress may have a negative effect on your mood, as your resources of norepinephrine and serotonin, two neurotransmitters related to general well being, are reduced or depleted. (Sapolsky, 2003) Environmental stress can also have a negative effect on prenatal brain development. Many developmental disorders, such as ADHD, Down syndrome, and Autism are linked to environmental stressors, such as emotional stress or smoking of pregnant mothers, or oxidative stress during prenatal development (e.g. Linnet et al., 2006). This would mean that children, who are raised in poverty and with stressed mothers, might be disfavored even before they are born. Nature, as it seems, is not at all fair.
As overstimulation of the nervous system can have a detrimental effect, so can under stimulation.
The brain is very plastic, altering its underlying structure from experience. This phenomenon, called neuroplasticity, occurs when connections between neurons are added or removed, or when new cells are added. Originally, it was believed that besides the hippocampus, the brain was only plastic in childhood. Humans were believed to have certain critical periods during their development when certain brain functions were developed. If the child was deprived of the appropriate environmental stimuli during the critical period, it would be almost impossible to develop the function later in life. One example of such a function is language. A famous case study of a girl with the pseudonym Genie, who was isolated from human contact until the age of 13, found that she was unable to develop grammatically correct language later in life. It was believed that this was due to the fact that she had not been exposed to spoken language during her critical period in early childhood. As most case studies, this study has a problem with generalizability. Early EEG studies of Genie’s brain suggested that she had a developmental disorder, but some researchers claimed that her abnormal brain activity could just as well have been due to her traumatic experience. (Cronkite, 2007). Later studies have shown that even though it seems to be critical periods where some behaviors are easier to be learned, especially in early childhood, new findings suggest that all parts of the brain is highly plastic, even after childhood.
If an organism is raised in an environment deprived of stimulating stimuli, studies show that it will have a negative effect on brain development. Many animal studies demonstrate that animals raised in richer, more stimulating environments, will have increased number of synapses, a thicker cortex and more complex neuronal connections (As cited by Crane, & Hannibal, 2009, p. 46). Examples of enriched environments are those that allow for social interaction, play and exploration. Genie’s signs of developmental dysfunction might well have come from her being raised in a deprived environment.
Due to the ethical issues and methodological problems of investigating biological processes in humans, the core of the background research of the theories of stress and neuroplasticity is based on animal studies. It does however not mean that human research is lacking. Many case studies on people with brain dysfunction have confirmed the plasticity of the brain, even later in life. There are also few that doubt that stress can have a negative effect on our body functions. Improved neuroimaging technology used on humans is constantly confirming hypotheses on brain function first suggested from studies on non-human animals. In light of evolution, it is also possible to assume that our brain function is very similar to our closest relatives in the animal world. How similar this resemblance is of course open to discussion. Another controversy is also whether there is less plasticity for some brain function than others as well as the extent of stressors’ influence on physiological processes. Most of the research has focused on plasticity of motor, sensory, language, music and memory functions, but the level of plasticity of each function it is still unclear. After all, the brain cannot be completely plastic, as there must be individual differences, such as talent. Further on, as research also has shown, the brain is not completely plastic, as there is also a certain level of modularity in the brain (e.g. Cosmides & Tooby, 1994). The plasticity of the brain is also expected to decrease with age. Further on, the effect of deprivation still needs more investigation. If an organism is deprived of a certain stimuli, for instance visual stimuli, it has been shown that other areas in the cortex take over those unused neurons. Being deprived of a certain stimuli may therefore improve another function in the brain. This is the reason why congenitally blind people usually have better hearing and touch sensations.
It is important that one does not fall into the false belief of the total freedom of your brain and your abilities because of plasticity. I doubt that I will ever become a famous football player or musician as I have never practiced those skills at an early age. Likewise, one cannot believe that threshold levels for stress are the same for everyone. The breaking point for any person under stress is very individual and depends on experience and vulnerability. One must also interpret the findings with caution as the underlying physiological processes are still largely unknown in detail. It must also be acknowledged that environment is not the only influence on our brains. It seems fairly palpable that our cognitions and behaviors play a significant role as well. Some studies on Buddhist monks have for instance shown that meditation alters brain structure significantly (N.A., 2005). If we believe in our free will it is also reasonable to believe that we have the ability to choose our environments, unless we are imprisoned.
The findings of these studies are nevertheless scientific enough to draw a few conclusions and to apply in society. Today, many patients with brain damage are helped by this basic research. Stroke patients, are being trained to recover some of their lost functions through music therapy. Other people are also learning to control their stress or disabilities through biofeedback which follows the same underlying principles of neuroplasticity. We should also continue to protect children and adults from extensive stress, as it can have a negative effect on them. One must however be aware of the individual differences in stress resilience. Most importantly, you should know your own limit. Unless you stress yourself too much, it is good to enrich your life with many activities. The best principle in life seems to be one of moderation, constantly enriching your life, but to avoid getting burned out. It may also be a good idea to visit your grandparents more, and as you get older, continue to use your brain. One way to do this could be to continue to learn more about the wonders of the brain. There is much to be learned.
by
jaymehta16031996 (student)
