I do not know a thing about this syncrometer but I can tell you that this is faulty testing. Foremost you have to understand that garlic will detoxify and it also is a natural antibiotic, therefore, when a person just starts to use garlic they will go into an auto detox and smell like garlic to high heaven, but over time of continued use you will not detect garlic on a person unless! they are ill and it is detoxing/killing off harmful things in your body. If it is affecting the brain as you suggest, I would speculate that it is removing harmful deposits in the tissue. Also, there is nothing mentioned here whether or not this was "organic" or mainstream garlic used in your testing. Regardless, I think this has some serious flaws in it. I eat garlic weekly, approximately one bulb of it or sometimes more. I do not have any of the above side effects as you suggest. No one can detect garlic on my body or breathe unless I have an infection or am ill.
Note: I have used garlic for 15+ years and when experiencing illness I consume a lot of it raw, results are that I feel better, think clearer and sweat the virus out quickly.