What's the meaning of "sliding scale" in this context?
(The quiet power of introverts) https://youtu.be/o1Y4Z0oh1GE?t=122

(Previous context: explanations about extroverts)
But introverts are more sensitive to dopamine. That's why we prefer the more slow-burn feeling we get when our brains release acetylcholine. That happens when we concentrate and focus our minds. It makes us introverts feel relaxed and content. But it barely registers with extroverts.
***Of course, like anything, it's a sliding scale.*** You can lean one way or another, or be a bit of both. Known as an ambivert.

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I've already looked up the definition of a "sliding scale" but still can't understand what it means is this context.
Can anyone explain this in a bit of detail? Thanks in advance.

Question

What's the meaning of "sliding scale" in this context?
(The quiet power of introverts) https://youtu.be/o1Y4Z0oh1GE?t=122

(Previous context: explanations about extroverts)
But introverts are more sensitive to dopamine. That's why we prefer the more slow-burn feeling we get when our brains release acetylcholine. That happens when we concentrate and focus our minds. It makes us introverts feel relaxed and content. But it barely registers with extroverts.
***Of course, like anything, it's a sliding scale.*** You can lean one way or another, or be a bit of both. Known as an ambivert.

-
I've already looked up the definition of a "sliding scale" but still can't understand what it means is this context.
Can anyone explain this in a bit of detail? Thanks in advance.

Answer

If you are on a  'sliding scale',  you lie somewhere between a range of values.

Imagine a drawn line between '0' and '10' with '0' being an extreme introvert and '10' being an extreme extrovert. The text is saying introverts and extroverts are on a 'sliding scale' where everyone's position varies a little. I could be an introvert at '3' and someone else could rank a '4' as they are slightly more extroverted. Someone at '5' on this imaginary line could be an ambivert - both introverted and extroverted in different ways.

So the author by saying 'it's a sliding scale' is saying introvert/extrovert aren't fixed values - they can vary. People can occupy a range of values. Two may be introverted for example, but one is still more introverted than the other.

Answer

This is a non-standard use of "sliding scale." There is no actual "sliding scale" here, but an analogy: just as with (for example) sliding scale payment, where if I am poor you charge a little money, if I am rich you charge more money for the same service--so here, if the brain is more sensitive to a neurotransmitter, a little of it has a big effect; if the brain is less sensitive, it takes a lot to have a bit effect.

Answer

It depends from person to person. 
They often talk about the “autism spectrum” the same way. Some people have many introverted characteristics and some people do not.