Particular foods have been shown to boost the production of these neurotransmitters but usually not by enough to make a perceptibledifference in the brain.
某些特定食物确实被证明能够促进这些神经递质的产生，但还不足以使大脑产生可见变化。
2
At the age I am writing these reminiscences a difference of 4 years is not perceptible.
以我现在写回忆录时的年纪，四年的年龄差别是看不出来的。
3
The difference is scarcely perceptible to the average reader.