An Investigation into the effect of caffeine on reaction times

Sophie Catt Centre: 64890

Candidate: 5045

An investigation into the effect of caffeine on reaction times and short term memory

Aim

To investigate the effect of varying doses of caffeine on performance in simple reaction time and short term memory tests.

Research and Rationale

Having carried out the core practical on the effect of caffeine on the heart rate of Daphnia, I wanted to investigate the effect of caffeine on other functions of the body, and how this effect comes about.

Caffeine is a natural pesticide, found in the leaves, beans and fruit of over 60 plants1, however in humans it acts as a central nervous system stimulant, reducing fatigue and restoring alertness2. It is said to be the most widely used drug in the world, with an average intake of 241mg per person, per day according to a Bristol survey3. I therefore decided to explore how it could affect reaction times and the extent of short term memory, as these are two factors involved in alertness.

It has a similar structure to adenosine, meaning it binds to adenosine receptors in the brain.

Caffeine and adenosine - http://en.wikipedia.org/wiki/Image:Caffeine_and_adenosine.svg - 22.10.08

When a nerve impulse travels through the synaptic knob, opening the Ca2+ channels, it triggers the release of adenosine, which is synthesised and stored inside the synaptic knob. Normally, the adenosine acts as a neurotransmitter when it is released into the synapse. It binds to the receptors in the membrane of the postsynaptic neurone, allowing the Na+ channels to open. However, if there is already caffeine in the synapse, it binds to the receptors, blocking the adenosine. The channels do not open4. The diagram on the following page shows this process.

Adenosine is normally released to protect the brain by slowing down neural activity. When caffeine prevents adenosine’s effects, the nerve cells are not restricted in their activity. The adrenal gland (situated above the kidneys) reacts to the increased neuron firing by producing epinephrine (also known as adrenaline), which causes the “fight or flight” symptoms: faster pulse rate, dilated pupils, raised blood pressure, higher blood sugar levels, tensed muscles etc5.

Reduced adenosine activity also contributes to increased dopamine activity5, a neurotransmitter which is a precursor in the production of epinephrine6. Together, these effects increase the levels of epinephrine in the brain. ADHD (attention-deficit hyperactivity disorder) is caused by a deficiency in dopamine, and its treatments raise dopamine levels7. This suggests that dopamine also plays a part in attention and concentration.

Synapse showing antagonistic action of caffeine on adenosine receptors - http://www.snabonline.com/pupil/mediabank.aspx -> Book artwork with no labels -> Figure 8.57 - 22/10/08

As well as blocking adenosine receptors, caffeine also blocks the removal of cAMP (cyclic adenosine monophospate) from cells. The build-up of this cAMP prolongs the effects of epinephrine8.

Hypothesis

Caffeine will increase the levels of epinephrine and dopamine in the brain, increasing alertness and concentration levels, therefore improving reaction times and short term memory.

Statistics Test

As I am comparing the effect of one continuous variable on another, I will use the Spearman Rank Correlation test. This requires a minimum of 5 pairs of measurements, so I plan to use 6 doses of caffeine, and no caffeine. At the p=0.05 level, the critical value for 7 pairs of measurements is 0.7149. Therefore rs must have a value greater than 0.714, where

rs = 1 – 6 Σ D 2

n(n2–1)

Null Hypothesis

Caffeine will have no significant effect on the reaction times or short term memory of participants.

Equipment

Method

The 7 doses I will use range from 0mg to 300mg in 50mg intervals. This is for safety and ethical reasons, because more than 300mg can cause “caffeine jitters”: irritability, anxiousness, restlessness, and/or diarrhoea10. I will give them a medical questionnaire (see appendix A) to sign before taking part in the experiment. I will ask if they have had an adverse reaction to caffeine before, because it is likely that they could react badly to it again. Caffeine causes the heart rate and blood pressure to increase, so I will ask if they have heart problems. In addition, caffeine increases gastric acid production11, which could worsen any stomach ulcers.

I will use 9 female volunteers aged 16-18. I am using all females instead of a mixture of males and females to control the variable of gender. There are 9 participants so that I will be able to get a reliable set of results and so that any anomalies are obvious.

The participants will be given their dose of caffeine at 9.20am each day, as the drug takes 45-60 minutes to reach its optimum effect. At 10.15am they will use the “Sheep Dash”12 game to test their reaction times, and the “Simon Says”13 game to test their short term memory.

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The first day, the test will be taken with no caffeine. Each consecutive day, I will increase the dose by 50mg, until the dose reaches 300mg. If, at any point, one of the participants has an adverse reaction to the caffeine, they will not be permitted to continue with the experiment. At the doses I have chosen, any adverse reaction to the caffeine is most likely not serious. The volunteer may get restless, experience tachycardia (high pulse rate) or get a headache14. If this happens, they will be given water to sip and told to sit down in a cool room.

The volunteers will be banned from drinking coffee, tea, energy drinks and other caffeinated drinks for the days of the experiment, and the weekends before and in the middle. This is to prevent any caffeine already in the body from affecting the test results. In addition, if the participant usually has a high intake of caffeine, they may suffer caffeine withdrawal. This peaks after 36-48 hours, depending on the level of caffeine tolerance, and any impaired performance should wear off in 3-4 days15.

The performance may also be affected by the volunteers improving at the tests over the course of the two weeks. Any improvement could be due to practise instead of caffeine dose. However, it is important that the dose is increased gradually so that they are not given a dose that is too high. I will take this into account when analysing my results.

Controlled variables

Preliminary testing

To ensure my method works, I will carry out preliminary tests. I will take the results for six volunteers at a dose of 0mg caffeine, as a reference, then two will take 100mg, two will take 200mg, and two will take 300mg. I will then compare the results with caffeine to the results without. This will give me an idea as to whether my range of doses is sufficient to give conclusive results, or whether the caffeine does not have enough of an effect to measure. The volunteers will take the caffeine pills at the same time as they will in the real experiment.

These results show that for 4/6 of the volunteers, reaction time decreased with caffeine, and for 4/6 the length of the longest sequence remembered increased. It is worth noting that the two people (CE and CF) for whom the caffeine had a detrimental or no effect were the same for both tests. There seems to be no correlation between the dose of caffeine and the improvement in performance.

After reviewing my method, I have decided to measure an additional dependent variable: the blood pressure of participants. This will hopefully give a more objective result, as the volunteers could improve at the games over the course of the two weeks, but they are very unlikely to be able to lower or increase their blood pressure significantly over this time period.

The extra equipment I will need is a sphygmomanometer (blood pressure monitor). The type I will use is automatic, so all I need to do is put the cuff on the unclothed upper arm, with the cable pointing downwards, and press the button.

The extra variables involved with taking blood pressure are as follows:

Results

After 3 days of doing my experiment, I reviewed my results. As I could still not see any clear pattern, I decided to also record the number of hours of sleep each volunteer had the night before the test.

On the day of 250mg, CE felt unwell, so she was advised not to continue to 300mg.

Hours of sleep

I could not see any clear correlation between the number of hours of sleep and the performance on the tests.

Reaction times

Short term memory

Blood pressure

The error bars in the graphs below indicate one standard deviation either side of the average result.

Statistics tests

Spearman rank correlation coefficient:

rs = 1 – 6 Σ D 2

n(n2–1)

At the p=0.05 level (there is a 5% probability that the results are due to chance), rs must be greater than 0.714 to indicate a significant correlation.

Null hypothesis: the dose of caffeine has no significant effect on the reaction times, short term memory, or blood pressure of participants.

Reaction times

Short term memory

Systolic blood pressure

Diastolic blood pressure

Analysis and Evaluation

With the use of my statistics tests, I can reject my null hypothesis for short term memory. However, at the p=0.05 level, my results support the null hypothesis for reaction times and both values of blood pressure.

Looking at the results and the graph, caffeine seemed to have a positive effect on reaction times, although it is not as great an effect as I expected. The one anomalous point appears to be at 250mg, where the average reaction time was slower than the reaction time at 0mg. This could be attributed to “caffeine jitters”, where the participants got anxious and started to “jump the gun”, but it is not seen at 300mg as would be expected if this was true.

I believe that the “Simon Says” game was the easiest to improve on, so the level of p should probably be higher, as it is very likely that the participants would have improved over the two weeks anyway. This therefore suggests that the correlation is not so significant, even though the rs is higher than the critical value. To test this theory, I could compare one group (not on caffeine) alongside the original group, to determine how much of the improvement is due to caffeine and how much is due to practice.

While carrying out the experiment, I found that I did not have time to let the participants rest for 10 minutes before taking their blood pressure. This will have caused some of the blood pressure readings to be too high, as the volunteers had to walk up stairs etc, just before taking the tests. I cannot therefore be sure that the general trend in blood pressure was solely due to caffeine. As mentioned, this error would be minimised by letting the volunteers rest for 10 minutes, however this was not practical in the time I had.

One reason for my results not being as expected could be due to the time I took them. Caffeine will only have an effect if it is blocking the adenosine receptors, so if there was no adenosine being released because the participant was not tired, caffeine would not block the effects of adenosine16. This might have happened because the time was late enough to allow the participants to fully wake up, but not so late they were tired.

Conclusion

Having analysed and evaluated my results, I conclude that caffeine (at the doses that I tested) does not have a significant effect on reaction times, short term memory, or blood pressure.

Appendices

Medical Consent Form

Have you ever experienced any of the following:

An adverse reaction to caffeine
Heart problems
Stomach ulcer

I consent to being given doses of up to and including 300mg of caffeine (the equivalent of approximately 3-4 cups of coffee).

I understand that I can drop out of the study at any time, and that I will be advised to drop out if I suffer adverse effects.

I will notify Sophie Catt if I feel unwell at any point during the study.

Signed ______________________ Date ______________

Sources

Caffeine-producing Transgenic Tobacco – accessed 14/10/08. http://www.isb.vt.edu/news/2007/artspdf/apr0704.pdf

Hiske van Duinen, Monicque M. Lorist, and Inge Zijdewind - The effect of caffeine on cognitive task performance and motor fatigue - October 2004.

Dietary Caffeine and Health Study – accessed 22/10/08. http://caffeine.psy.bris.ac.uk/results.htm

Interactive tutorial: Activity 8.4, Crossing a Synapse – accessed 22/10/08. http://www.snabonline.com

Why does caffeine keep you awake? – accessed 22/10/08. http://science.howstuffworks.com/question531.htm/printable

Newcastle University Centre for Cancer Education – accessed 24/10/08. http://cancerweb.ncl.ac.uk/cgi-bin/omd?dopamine

Psychiatry Online – Clinical and Research News – accessed 24/10/08. http://pn.psychiatryonline.org/cgi/content/full/36/6/35

Wellesley College’s chemistry pages – accessed 24/10/08. http://www.wellesley.edu/Chemistry/Chem101/caffeine/caffeine.html

H. T. Hayslett – Statistics Made Simple, published by W. H. Allen & Co, 1979. Pages 180-184 and 230.

About.com: Nutrition – accessed 24/10/08. http://nutrition.about.com/od/askyournutritionist/f/caffeine.htm

Caffeine – Drug information – accessed 19/11/08. http://www.medic8.com/medicines/Caffeine.html

BBC – Science and Nature – Human Body and Mind – accessed 24/10/08. http://www.bbc.co.uk/science/humanbody/sleep/sheep/

Simon Says game – accessed 16/11/08. http://www.freeonlinegamescartoons.com/puzzlegames/play_memory_test_game_free.htm

Coffee FAQ – Caffeine FAQ – What happens if you overdose? – accessed 16/11/08. http://coffeefaq.com/site/node/12

BBC – The Truth about Food series - Does caffeine give us a mental edge? – accessed 24/10/08 http://www.bbc.co.uk/sn/humanbody/truthaboutfood/best/caffeinebrain.shtml and video on http://www.bbc.co.uk/sn/humanbody/truthaboutfood/flashapp/

Society for Neuroscience – Adenosine and Sleep – accessed 18/12/08 http://www.sfn.org/index.cfm?pagename=brainBriefings_adenosineAndSleep

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Peer Reviews

Here's what a star student thought of this essay

skatealexia

9th of Mar 2012

Quality of writing

Grammar and punctuation good. Spelling mainly good apart from one or two words e.g. practise should be practice.

Level of analysis

The background and hypothesis and scientific reasoning behind the experiment are analysed and explained to a very high level. Choice of statistical test is adequate. Uses a selection method and tries to rule out anything that could be a confounding factor a level that I would expect of only the highest of A level candidates. Addresses any adverse affects caused by the caffeine very well indeed. Carry out a preliminary test to have a guideline and also to add on any other factors. Conclusion and overall analysis which include a range of statistical tests and graphs are all very good.

Response to question

An outstanding example for the level I would expect for A level biology. The introduction and hypothesis are very good with a very high level of detail. The main body and conclusion are also completed to a very high level of detail with a clear response throughout the essay.

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