Shaina Danet
Introduction
For humans, activities require active use of our brain to decode
information and store it into our long term memory. One place where the brain
stores the information it acquires is the hippocampus, particularly spatial
recognition information (Martinez et al. 1982).Slightly controversial studies
have indicated the hippocampus is associated with recognition, but familiarity
is distributed to the other cortical areas (Fortin et al 2004). The brain uses
glucose as a food source to be able to run (Booth 1994 as described by Donohoe
and Benton 1999). Glucose is taken from the foods we eat during digestion, and
is released into the blood stream. Other substances, such as caffeine, have also
been shown to improve memory through increased alertness (Addicott and Laurienti
2009). Caffeine also shows evidence of increasing brain activity in general,
which decreases the time needed for the hippocampus to take in information and
create memories.
In order for the brain to function properly, there has to be a minimum
amount of glucose in the blood that can pass the blood-brain barrier and feed
the brain (Foster et al 1998). Evidence has suggested that one reason people
have cognitive impairments is from having consistent low blood glucose levels
(Foster et al 1998). The elderly particularly have this problem because of poor
glucose regulation; as the human body ages, the ability to metabolize glucose
diminishes, including having drastically reduced endocrine response to stress
(Gold 1986, 1992 as said by Foster et al 1998). When giving the elderly regular
doses of glucose, memory drastically improves (manning et al 1992, as said by
Foster et al. 1998)
In rodents and humans alike, there has been evidence that glucose
administration can enhance memory (Gold 1986, 1991, 1992, as described by
Donohoe and Benton 1999; Foster et al 1998; Canal et al 2005) as a result of
excess blood glucose, as well as individual differences in glucose regulation (Gonder-Frederick
et al 1987, Hall et al 1989, Benton and Owens 1993, and Benton et al 1994, as
described by Donohoe and Benton 1999). Glucose has been shown to have positive
effects on healthy adults, and improving cognitive function in adults with
memory problems (Foster et al 1998). While most information on the effects of
glucose on the hippocampus has focused on memory tasks, there has also been
evidence that glucose can contribute to better scores on some non-memory tasks (Donohoe
and Benton 1999). Owen et al (2010) found that higher dosages (60g compared to
20g) of glucose showed more of an improvement with word recall and delay than
the lower dosage. This went against previous research, which found little
difference between two dosage levels, though they were closer in amount (2010).
Kanoski and Davidson (2010) found that high energy diets can actually impair
cognitive function and memory. Therefore, previous data suggests that there is a
limit to what a human’s body can handle when it comes to energy being consumed
and how much glucose is being released into our blood streams.
An outside chemical that can have a beneficial effect on memory
conversion is caffeine. Caffeine has been shown to enhance memory despite
different processes of ingestion (acute, slow delivery, long intermittent
consumption) (Cunha and Agostinho 2010). However, other research directly
counters the supposed effects of caffeine (Childs and deWit 2006, as told by
Cunha and Agostinho 2010). Caffeine is believed to aid memory processing by
producing a neurostimulant that provokes adenosine and allows the neurons to be
disinhibited (Nehlig 1999 and Ferre 2008, as told by Addicott and Laurienti
2009) as well as increasing cerebral energy metabolism and cortical activity (Arendash
et al 2009).The drawback of constant exposure to caffeine is that it reduces the
effects that it would have compared to an acute dose (Addicott and Laurienti
2009). There also has been evidence that chronic exposure of caffeine will
affect the A1-CB1 receptors in the hippocampus, altering
how the brain translates spatial memory (Souse et al 2011). Along those same
lines, Arendash et al found that mice who had exhibited the signs of alzheimers
actually stopped and slightly reversed memory impairment with a moderate dose of
caffeine daily (2009).
While previous research has independently assessed the role of glucose
and caffeine on memory development, there has yet to be an experiment
simultaneously comparing the separate effects of these two compounds. I examined
how variable concentrations of glucose and caffeine affect memory in mice using
a maze. I had predicted that higher concentrations of glucose and caffeine will
have increased memory retention. In addition, I had predicted that glucose will
have a greater effect on memory and learning time compared to caffeine.
Methods
Preparations:
Forty mice (Mus musculus) were
housed two to a bedded cage, separated by sex, at room temperature with food
pellets and water available in the animal room at McKendree University. The mice
were kept under a twelve hour light period where the lights were constantly on.
Each treatment had cages of eight mice, four females and four males, and the
cages for each treatment were grouped together. The five solution treatments
that were used to study the effects of glucose and caffeine on memory and
learning time were 9% saline solution for control, 2mg/kg glucose, 4mg/kg
glucose, 2mg/kg caffeine, and 4mg/kg caffeine. The saline solution was made in a
9% sodium chloride in DI water solution. The four other solutions were made with
saline solution and either crystallized glucose or caffeine powder mixed in.
Each mouse was weighed to the nearest gram, then the weights were used to
calculate the 2mg substance/kg weight of mouse or 4mg/kg dose that each mouse
would receive per 1mL shot. This information was used to create the stock
solutions that were kept in 1L bottles. 15mL at a time were portioned into 30mL
bottles for easier handling
Trials:
Between October 8th-24th, and February 4th- March 1st I ran trials every Monday,
Wednesday and Friday for a total of nine trials. The trials were always started
at the same hour. The day before the maze test the mice had their food taken
away for fasting [18-24 hours before the trial]. During the testing, the two
mice from each cage were moved to a larger holding area where they were given
1ml shots of their respective solution to the base of their tail. After waiting
about four minutes for the solution to move into the blood stream, one mouse at
a time would be placed at the start of the maze and timed from when they touched
the start of the maze until they approached the end of the maze. The food
pellets, as well as treats such as chocolate and peanut butter, were placed at
the finish line as incentive for the mice to move to the end of the maze. When
the mouse approached the food at the finish line the mouse was placed back in
their cage with a handful of food. After five trials the maze was reversed for
another four trials. This was to keep the data consistent with creating new
memories of the maze, instead of timing memory recall. The times for each mouse
were averaged based on the maze used and used in the ANOVA. An average of all
the mice for each treatment was then done to see if there was a pattern across
variables for each maze. The time versus variable data was run with a one-way
ANOVA to examine across glucose and caffeine times, as well as the 2mg and 4mg
concentrations. The data collected was put into the one-way ANOVA in three
groups: Average 1, the variable, and average 2.The ANOVA was run twice, either
with average 1 and the variable, or average 2 and the variable, the variable
being the dependent factor. The post-hoc test used was the Tukey test.
Results
Figure
1
The average times across treatments for the mice to complete Maze 1; the 2mg
caffeine had the shortest average time. (p=.137)
This shows the comparison of the average times of each treatment. The control
group had an average of 1.96 minutes to run the maze. The 2mg Glucose and 4mg
Caffeine treatments had a higher average time than the control(2.35 and 2.17
minutes), but the 4mg Glucose and 2mg Caffeine groups had a shorter time(1.81
and 1.68 minutes), with the 2mg Caffeine group having the shortest average time
on maze one. The results were not significant between the groups, however (p=
.137).
Figure
2
The average times across treatments for the mice to run Maze2 ; 2mg Glucose had
the shortest average time, and only 2mg caffeine as at/above the control time.
(p=.485)
The averages for the second maze also had unexpected results. Compared to
the control (1.08 minutes), 2mg Caffeine had the same average time. 2mg Glucose
had the shortest time with .67 minutes, and then 4mg Glucose with .93 minutes,
and finally 4mg Caffeine close behind with .95 minutes. There was also no
significance between the groups (p=.485). The level of standard deviation is
much greater in figure 2 than figure 1 as well.
Discussion
Based on previous research, one would expect glucose and caffeine to have better
results than the control. The results for this current experiment came to be
vastly different from the literature used. There was no significance between any
of the groups, and even in figures 1 and 2 one can see that certain treatments
actually had a higher time average than the control. Previous work confirmed
that glucose helps increase memory for certain tests, and could even reverse
poor cognitive function (Foster et al 1998, Canal et al 2005, Donohoes and
Benton 1999, Owen et al 2010). Owen et al found that a higher concentration of
glucose (60g) showed significant results compared with placebo, while a lower
concentration (25g) did not. In the same though process, caffeine has previously
been shown to increase memory retention as well as small improvements towards
cognitive deficiencies (Addicott and Laurienti 2009, Cunha and Agostinho 2010,
Arendash et al 2009).
Previous research has indicated that chemicals such as glucose and
caffeine can help improve memory and even alleviate certain cognitive disorders.
When the brain is transforming information into memory, the brain takes in large
amount of glucose to fuel it. If one takes in large amounts of glucose, the
brain will have plenty of energy to feed off of, which is supported by previous
research (Foster et al 1998, Canal et al 2005, Owen et al 2010). As for
caffeine, the stimulant capabilities of caffeine will increase alertness,
meaning that the brain is paying special attention to the information flowing in
from the senses. When we pay more attention to our surroundings, we are able to
help our memory retention, as compared to when a person is fatigued. The fact
even chronic caffeine drinkers show memory retention improvement, as compared to
the vast increase for acute drinkers, suggests that this increased awareness
really does make the difference in memory retention (Addicott and Laurienti
2009). Both glucose and caffeine have also shown evidence of improving and even
reversing cognitive defects (Cunha and Agostinho 2010, Arendash et al 2009,
Kanoski and Davidson 2010).
My results are contrary to the results given by my sources. First, there
is no descending pattern of averages between the control and the other
treatments as would be expected if glucose and caffeine improved memory
retention(fig.1 and fig 2). In fact, some of the groups had a longer time
average than the control. Also, if higher concentrations of the two solutions
really do improve memory retention better than the lesser concentrations, then
there would be a trend that the 4mg doses would be smaller than the 2mg doses.
In reality there is a mixture between which dosage is shorter between glucose
and caffeine, and between the two mazes. Additionally, we find that the results
are not significant. This information rejects my original hypothesis that
glucose and caffeine have a significant effect on memory retention.
My results would show that glucose and caffeine does not have much of an
effect on the brain, not readily increasing memory retention. This could be just
an unusual result, which does happen, or could possibly provide clues towards
the specificity of how these two substances help memory. Individuals may be
affected differently by different substances, but since this experiment has a
large enough testing group that can be ruled out. Another possibility is that
the maze testing with a goal for food may not be sufficient for testing the full
capability of glucose or caffeine on memory. My research can be used, along with
other research that showed no significant results, to determine if there are
certain processes within the body that can use external substances to enhance
function, or dispose of it normally through waste. There may be a biological
process that determines whether the brain will be enhanced with extraneous
glucose or caffeine.
New experiments should test whether other memory retention test provide a
better result towards memory retention testing. Some memory tests are simply
unaffected by glucose and caffeine additives. Also, one could see if there is a
difference between injecting the mouse with the solution vesus having them
ingest the glucose or caffeine with normal tap water.
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