The ancient Greeks developed basic memory systems called mnemonics. The name is derived from their Goddess of memory "Mnemosyne". In the ancient world, a trained memory was an 
immense asset, particularly in public life. There were no 
convenient devices for taking notes, and early Greek orators delivered long speeches with great accuracy because they learned the speeches using mnemonic systems. The Greeks discovered that human memory is largely an associative process that it works by linking things together. For example, think of an apple. The instant your brain registers the word "apple", it recalls the shape, color, taste, smell and texture of that fruit. All these things are associated in your memory with the word "apple". 
This means that any thought about a certain subject will often bring up more memories that are related to it  . An example could be when you think about a lecture you have had. This could 
 trigger a memory about what you're talking about through that lecture, which can then trigger another memory. Associations do not have to be logical. They just have to make a good link. An example given on a website I was looking at follows, "Do you remember the shape of Austria? Canada? Belgium? Or Germany? Probably not. What about Italy though? If you remember the shape of Italy, it is because you have been told at sometime that Italy is shaped like a boot . You made an association with something already known, the shape of a boot. And Italy shape could not be forgotten once you had made the association." 

     


sometime 以前的某个时间 some time 未来的某时，一段时间 sometimes 有时 some times 好几次 mnemonics 记忆术 orator n. 演说者；演讲者；雄辩家；原告 immense adj. 巨大的，广大的；无边无际的；非常好的 texture n. 质地；纹理；结构；本质，实质 trigger 触发;引起