Back in the 1980's, in his research on human brain function, Dr Robert [Bob] C. Beck, DSc. found that garlic has a detrimental effect on the brain. He found that in fact garlic is toxic to humans because its sulphone hydroxyl ions penetrate the blood-brain barrier and are poisonous to brain cells.
Dr Beck explained that as far back as the 1950s it was known that garlic reduced reaction time by two to three times when consumed by pilots taking flight tests. This is because the toxic effects of garlic desynchronize brain waves. "The flight surgeon would come around every month and remind all of us: "Don't you dare touch any garlic 72 hours before you fly one of our airplanes, because it'll double or triple your reaction time. You're three times slower than you would be if you'd [not] had a few drops of garlic."
For precisely the same reason the garlic family of plants has been widely recognized as being harmful to dogs."