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The Effects of Stress on Short-Term and Long-Term MemoryMarni Rossmanmrossman@utk.edu

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The Effects of Stress on Short-Term and Long-Term Memory

Marni Rossman

Chancellors Honors Project Senior Thesis

Faculty Advisor: Srinivasan Mahadevan

Fall 2010

Rossman 2

Marni Rossman

Faculty Advisor: Srinivasan Mahadevan

Chancellors Honors Project Senior Thesis

Fall 2010

The brain is a complex structure at the center of our central nervous system.

Comprised of billions of neurons, it is continually receiving and sending our signals to

different body parts through our sympathetic and parasympathetic nervous system.

Depending on various types of injury, illness, and stressors, the short term and or long term

memory capacity may be deteriorated. Throughout this paper I will analyze the different

causes and consequences of stress on the brain.

The central nervous system, containing both the brain and the spine, along with the

peripheral nervous system control most of our every day functions. The brain is split into

different lobes: the frontal, parietal, occipital and temporal lobe. The temporal lobe is most

notably associated with the storage of memories. Of particular importance is the role the

hippocampus, amygdala, and prefrontal cortex play in the brain when involved with both

acute and chronic stress.

The hippocampus is the brain’s main memory center. This paired structure is located

in the medial portion of the temporal lobe and deals primarily with special memory and long

term memory. It functions to process short term memory by converting it to long term

memory. The amygdala, located deep in the temporal lobe, deals with emotional memory.

This includes fear conditioning and memory consolidation. Lastly, the prefrontal cortex deals

with more complex and goal orientated functioning. Located in the anterior portion of the

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frontal lobe, the prefrontal cortex helps to keep the amygdala from overreacting to the stress

response.

The different regions of the brain are affected differently by stress. These stressors

may affect the short term and long term ability differently depending on the source of the

stress, the duration of the stress, the intensity of the stress, and the timing that the stress

occurs in the memory phase. Primarily, the limbic system deals with stress and anxiety. It

had such a strong influence on memory and emotions that it is also known as the emotional

brain. When an area of the brain is stimulated by stress, the limbic system responds through

the autonomic nervous system through its endocrine glands that automatically help to control

our metabolic system (The Franklin Institute).

It is also important to distinguish between the different types of memory: short term

memory and long term memory. Short term memory, also known as active memory, lasts for

only a matter of seconds. It holds information in the brain for short amounts of time, this way

keeping the information readily accessible. Our memory span for our short term memory is

very limited, although there are ways to help convert short term memory to long term

memory.

Long term memory may last from a few days to decades. This includes episodic,

semantic, and procedural memory. With episodic memory we are able to recall specific dates

and events in time. This usually includes personal experiences. Our semantic memory helps

us to recall knowledge about our external world. This is generally facts and rules about

general information. Lastly, procedural memory includes remembering the order for

performing specific tasks.

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There are many chemicals involved with the stress response in the human body.

Glucocorticoids are steroids that are made in the adrenal gland. The primary glucocorticoid

released when the body perceives a threat is cortisol. When the brain tries to send a signal out

to the body, cortisol will interfere with the ability of the neurotransmitters to communicate.

This, therefore, makes it difficult to retrieve information from our long term memory (Your

Amazing Brain).

Cortisol is released through an elaborate process. First, the hypothalamus signals to

the pituitary gland (located at the bottom of the brain) to release chemicals that. Within only

a matter of minutes, those chemicals reaches the adrenal cortex. They then sell the adrenal

cortex to secrete cortisol, which is then distributed throughout your body through your

bloodstream (Your Amazing Brain).

Other important chemicals in the stress response include corticotrophin and

epinephrine. Corticotropin is secreted in the hypothalamus in response to stress and anxiety.

Epinephrine is a type of adrenaline. The Adrenal glands release epinephrine to tell the body

to increase its breathing, heart rate, and blood pressure (The Franklin Institute). This,

therefore, moves along more oxygen to the brain and muscles allowing the sympathetic

“fight or flight” response to occur.

After a certain amount of cortisol has been released into the body, the body tells itself

it needs to rid itself of the steroid. Hormones are then secreted and sent to go to the adrenal

glands and the brain to retrieve the excess cortisol. The hormones then transport the excess

cortisol to the kidneys to remove it from the body, therefore returning the body to more of a

state of equilibrium (The Franklin Institute).

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The Yerkes-Dodson law reveals the relationship between stress and memory. With a

low amount of stress, memory formation does get better. Once it reaches a certain level and

the amount of stress becomes too high, the ability to form and recall memories from ones

long term and short term memory becomes debilitated. This demonstrates why concluding

whether or not an event will become a memory depends on the levels of stress around the

time of the event (Lukowiak).

With short term stress, one may experience physiological changes that enhances

behavior and helps to override challenge. Once that stress becomes chronic, those same

physiological changes that enhanced behavior become detrimental to one’s body. This is due

to the activation of the hypothalamic, pituitary, and adrenal glands of the body that cause the

secretion of cortisol in response to stress (Cazacoff).

When one really starts to notice the effects of stress on the brain is when it has

encountered a form of chronic stress. This causes an over secretion of the stress hormone, as

it goes out to collect the excess cortisol in the body. When the body encounters an adrenaline

rush, it also comes across hypertension (an increased level of blood pressure), increased

abdominal fat, and decreased bone density, all of which are detrimental to the body (The

Franklin Institute). This is when our parasympathetic and sympathetic nervous system come

into play, as the parasympathetic fights for the body to rest and digest and the sympathetic

nervous system prepares the body for a fight or flight response.

This overexposure to chronic stress is what is proven to cause damage to the brain,

especially the hippocampus. Once the hypothalamus detects a threat, it causes the pituitary

gland to secrete a hormone which in turn causes the adrenal glands to secrete cortisol. Once

the amount of cortisol in the body reaches a certain level, the hippocampus tells the

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hypothalamus to turn off the mechanism causing the secretion of the cortisol. Once the brain

has been over affected by the effects of the cortisol the hippocampus may become damaged

through neuron death (Cheryl).

This damage to the hippocampus causes it to be unable to provide the proper feedback

loop to the hypothalamus needed to stop the secretion of the cortisol. Consequently, cortisol

is continually secreted in the brain with no source to tell it to stop, leading to diminished

memory (The Franklin Institute). This stress hormone also causes the amount of blood

glucose reaching the muscles to be diverted, causing the amount of blood glucose (and

therefore energy as well) reaching the hippocampus to be diminished as well (Your Amazing

Brain).

In neuroimaging studies that look at the effects of the stress hormone on memory we

find results leading to the conclusion that deteriorated memory does occur along with chronic

stress. By raising the level of stress using stimulus material, such as pictures and film, or

through social evaluative threat situations (also known as stress tasks), Anda van Stergeren

was able to obtain neuroimaging of the brain during these responses to stress. He found that

high levels of stress, leading to the release of high levels of cortisol throughout the body, led

to impaired memory performance. Also found was that highly involved with this stress

response were the amygdale and hippocampus (van Stegeren). These results prove further the

correlation between high levels of stress and stress hormones with impaired memory retrieval

in the brain.

In studies done on rats injected with cortisol, researchers found that after several

weeks the rats did experience death of brain cells. Primary affected was the hippocampus, the

area responsible for episodic memory (The Franklin Institute). There is also evidence of

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reduced density of the hippocampal dendritic spines of rats due to stress (Chen). This gives

only more evidence that the brain does experience diminished memory levels when override

with the steroid cortisol.

In a study at the University of Zurich in 2000, McGaugh studied thirty-six healthy

adults. He asked them each to memorize a list of sixty nouns that were each displayed for

about five seconds one a computer screen. Half the subjects took a pill containing cortisone

(a precursor of cortisol) while the other half took a placebo pill. The pill was either taken an

hour before the first presentation, just after the word presentation, or an hour before the

retention test. McGaugh found that the subjects who took the cortisone pill did in fact

experience impaired memory, but only when taken an hour before the retention test. This

leads to the conclusion that the stress hormone cortisol did affect the subjects ability to recall

old (but no recent) memories (The Franklin Institute). It is important to note that all

chemicals in response to the stress hormones are not all negatively correlated. There is such

thing as good stress that has proven benefits for the body. For instance, norepinephrine,

which is one of the primary excitatory neurotransmitters, is important in the creation of new

memories (The Franklin Institute). What seems to be paramount in this process is limiting or

managing the stress that reaches the sympathetic nervous system so that the body is not

constantly aroused and sending out the message of “fight or flight”, consequently releasing

increased amounts of cortisol.

Overall we find that excessive stressors lead to the release of chemicals in the body

that do seem to impair the long term and short term memory capacity. Although many

studies have been performed on humans of largely ranging ages, it is important to continue

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research in order to fully understand the types of stress and situations that lead to the

different amounts of diminished memory in the brain.

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