I kind of noticed similar when I've eaten garlic,however I'm not sure about all of what that report says. My analysis would be that 1)Garlic lowers blood sugar,therefore it could also lower the glucose going to the brain. What I do is eat or drink something with Sugar in it after consuming the garlic to insure it doesn't pull my glucose down too low.
2)Garlic is a known antiparasitic so it could also just be stirring parasites upon consumption.