No it's actually the lack of serotonin that causes the depression as well. There's sort of a problem writing the memories from short term to long term memory.
Basically the memories are there, but you can't find them. Like a hard drive with a bunch of stuff on it, but the computer doesn't know where the individual data is stored on the drive.
That's why, if someone tells you about something you experienced together in great detail, you'll sometimes be able to remember. And when that happens the memory's suddenly clear as day. They basically helped you locate that memory.
So, here are some tips to better your memory (produce more serotonin):
Eat a lot of proteins for breakfast and NO sugar. So instead of a peanutbutter jelly sandwich, maybe eat scrambled eggs and a bread with pepperoni. The further you can move your sugar intake to lunchtime, the better.
Pick a fixed sleep time. It absolutely doesn't matter when you wake up, 5am, 11am, all the same. BUT it matters a lot when you go to bed. This should be A) before 12pm and B) always at the exact same time.
I personally recommend 11pm (obviously you can go to parties and stuff but the more you stick to it, the better).
Self explanatory: Sport.
Some push-ups throughout the day or a quick 2 mile run in the morning is all you need really.
I know this is a lot of change, especially the sleep schedule thing, BUT the rewards are amazing. You'll feel way better, you'll remember more and have more energy for the things you love! (Effects can start to be noticeable after just two weeks). Think about it like this: people that want to loose weight have to do special diets that take a lot of effort, but the rewards are really improving their lives. The same way, these small changes can give you back so much joy in life.
I hope some of you will try it out! Stay save friends!