In an article in the British Journal of Nutrition, two types of mice were randomly selected. One group received a thyme supplement for a specific time, while another group was used as a control group and received no supplements. The brains of the mice were then analyzed, and it was found that the brains of the group of mice that received the thyme supplements had antioxidant levels similar to those of younger mice. It was concluded that the thyme supplement increased the antioxidants in the brains of the mice.

Identify the independent and dependent variables for each study.