Comparison of Microglial Activation in Severe Asthma and Healthy Controls

The goal of this clinical trial is to learn about how asthma influences brain function. The main questions it aims to answer are: * How airway inflammation in asthma affects the brain; and, * Whether airway inflammation in asthma is related to symptoms of depression and anxiety Over the course of 3 visits, participants will: * Complete questionnaires * Complete computer tasks * Undergo allergy skin test and breathing tests * Give two blood samples * Give a sputum sample * Complete brain imaging scans Researchers will compare results between participants with asthma, and participants who do not have asthma.