Re: The effects of stress on memory

	Ah, Rebecca, it’s seemingly simple questions like this that make me 
realize that we neuroscientists don’t know all that much.  The short answer 
is that stress does affect memory.  But, in some instances it can help your 
memory and in other instances it hurts your memory.  Now for the longer 
answer.
	First off, let me begin by discussing stress.  In biological terms, 
stress can be any condition which causes the release of certain hormones, 
called glucocorticoids, into the blood stream.  These hormones are released 
by a mass of tissue, called the adrenal gland, which lies on top of the 
kidneys.  Hormones are chemicals which are released by certain cells of the 
body, travel through the blood, and tell other cells in the body what to 
do; they are a kind of messenger.  Glucocorticoids are messengers which 
tell the body that it is in a stressful situation.  They tell the heart to 
beat faster, they tell the muscles to get ready to respond if needed, and 
they tell the stomach to stop digesting food.  Basically, they get the body 
ready to fight or run away from a stress.
	Now let me discuss memory.  There are many different kinds of 
memory.  Now you may think that memory is just the process of remembering 
something that happened in the past, and you would be partially correct.  
But people who study memory have found that there are many separate types 
of memories and many different parts of memories.  For example, there is 
memory formation, that is the process of making a memory.  There is memory 
retrieval, which is being able to remember a formed memory.  Formation and 
retrieval of memories are completely different processes as far as the 
brain is concerned.  In addition, there are visual memories which involve 
the memory of seeing things, there is auditory memory which involves the 
memory of hearing things, and there is spatial memory which involve the 
memory of where things are in space.  All of these types of memories use 
different areas of the brain.  These are just a few of the memory types and 
memory processes which scientists have so far discovered.
	So, what do we have so far.  We have a basic understanding of the 
biology of stress and a basic understanding of memory.  How do they fit 
together?  Remember, that the glucocorticoids which travel through the 
blood in times of stress affect many parts of the body.  They also affect 
the brain.  But the brain also has many different parts to itself, and 
these glucocorticoids can affect some parts of the brain more than others. 
Also remember that different parts of the brain are involved in different 
types of memory.   
	Glucocorticoids travel to the brain and can cause areas of the 
brain called the limbic system to work more and other areas of the brain 
called the association areas to work less.  In general, the limbic system 
of the brain is involved in the memory formation and the association areas 
of the brain are involved in spatial memory and to a certain amount memory 
retrieval.  Given this information, we might postulate that stress will 
increase the ability to make a memory, while at the same time make it 
harder to retrieve memories which have already been made.  Experimental 
evidence indicates that this is basically true.  For example, emotionally 
stressful events in a persons life are well remembered, as are other things 
that happened to that person during the same time as the stressful event.  
The stress, acting via glucocorticoids and the limbic system, has formed a 
stronger memory than normal.  On the other hand, stress can make it harder 
to retrieve old memories (especially spatial memories).  For example, we 
can train rats to swim in a pool of cloudy water which has a hidden 
platform somewhere in the pool.  The more times we put the rat in the pool, 
the quicker the rat will swim to the spot where the platform is (This is 
called a Morris Water Maze).  If we take rats which have been trained to do 
this but stress them by giving them electric shocks or placing them at a 
great height, then put them in the pool, they have a hard time remembering 
where the platform is.  This is because the Morris Water Maze tests the 
rats spatial memory.  You can also train a rat to respond to certain visual 
cues (for a food pellet reward).  In such tests, stress does not seem to 
have much affect.  This is because glucocorticoids do not have much affect 
in the areas of the brain which are involved in vision and the formation of 
visual memories.
	As you can see, there are no clear cut answers to your question.  
The truth is, that we just don’t know enough about learning and memory and 
how the brain functions to even put forward a good model of memory, let 
alone how stress can affect it.  The little that I have shared with you 
should be considered as general concepts of memory and stress, but it is 
far from 100% correct or complete.  I hope this gives you the background 
you need.  Good luck on your project.