How do I find recently trending topics in a particular area using google and other free search tools (e.g., memory improvement)

Hi, long story short, background in memory research, no job presently, I have been asked to write web content for a company that has a memory improvement course. Specifically, they asked me to come up with trending topics (about 15, during the next 4 months) related to memory and memory improvement (e.g., products, therapies, diets, techniques).

Pay works out to less than minimum wage, but I need to give it a try. My issue is I don't know how to do online search to find trending topics in a particular domain. I am not asking with direct help with my job but general guidance regarding how to find trending topics in a particular area using google or other online tools. Would be much appreciated.