Why do some drugs dilate your pupils?

Sarah Madden was wide-eyed answering Heather's question...

Sarah - The pupils are controlled by the muscles in our iris.

Chris - That’s the coloured bit isn’t it?

Sarah - That’s the coloured bit, yeah, that’s right. There’s two types: there’s one that’s a bit like spokes of a bicycle which causes your pupil to dilate (get bigger). And then there’s one which is called a sphincter (a bit like the muscle in your bum) which causes it to get smaller.

Chris - There’s a thought isn’t it - relating your eyes to your bum?

Sarah - It can happen in different ways for different drugs. When you have ecstacy this makes you very happy, which means it causes the release of a hormone called serotonin. This binds to - a word I’m using a lot today - a receptor in your brain and this carries on and causes your pupils to dilate (get bigger).

Chris - Philipe...

Philipe - Actually I think onto that, eyes also when you want to make a choice. If let's say you really want that apple and you don’t want that pear, your eyes will dilate more when you’re looking at the apple. And it’s the same thing when you’re trying to choose a mate. If you can see that, when you are aroused, your pupils are actually dilated. So look for that when you go on a date guys.

Chris - Sarah M…

Sarah - That’s a really good point. Scientists have started to wonder if they can read our minds through this pupil dilation. They did one experiment recently where the put a button in front of the participants and asked them to push in a 10-second interval. And they found they could predict when the participants were going to press it because their pupils dilated about one second before.

Chris - And that was the motivation?

Sarah - Yes, exactly. So they can hypothesise what’s going on but who knows what will happen in the future.