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30 September 2014
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You are here: BBC Science > Human Body & Mind > The Mind > Personality and individuality

Lemon juice experiment

Sucking a lemon
Sucking a lemon

The amount of saliva you produce after putting a drop of lemon juice on your tongue might tell you something about your personality.

Itís to do with a part of your brain called the Reticular Activating System (RAS) which responds to stimuli like food, or social contact. For example, it controls the amount of saliva you produce in response to food. A good food stimulus is lemon juice. Squeezing lemon juice on to your tongue makes your mouth water, and it does this because your RAS is responding to the lemon juice.

Scientists now think introverts have increased activity in their RAS and therefore increased production of saliva. The theory is that the RAS in introverts has a high level of activity, even when it isnít being stimulated. So it only needs a small stimulus to produce a large response. This means that introverts are likely to produce a large amount of saliva in response to lemon juice. But because the RAS also reacts to social contact, introverts react more strongly to meeting people too.

In extraverts, on the other hand, there is a low level of activity in the RAS when it isnít stimulated, so they require a much larger stimulus to generate a response. So they usually produce less saliva in response to lemon juice than introverts, but are more comfortable with social contact.

Try this simple test with your friends and family and compare your results.

The Test

You will need:

  • Lemon juice
  • Kitchen scales
  • Cotton wool balls

This is what you need to do:

  • Put a large drop of lemon juice on your tongue and swill it around your mouth for ten seconds
  • Use the cotton wool balls to mop up all the saliva that you produce
  • When youíve mopped it all up, put the cotton wool balls on your kitchen scales and see how much they weigh
  • Compare your results with your friends and family, and see whose weighs the most

We expect that you will find:

  • That introverts produce a lot of saliva in response to lemon juice
  • That extraverts donít produce much saliva in response to lemon juice

Now try our personality test and our Ďnecker cubeí experiment to see if they say you are more of an extravert or an introvert. And to find out whether the results from the lemon juice experiment tally up.

In our test, the introverts produced 50% more saliva than the extraverts. But itís worth bearing in mind that there are lots of other factors that affect saliva production, such as time of day and how thirsty you are.

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