bear in mind

If a person asks you to bear something in mind, they are asking you to remember it because it is important.
“You must bear in mind that the cost of living is higher in New York.”

(have a) brain/memory like a sieve

Someone who has a brain like a sieve has a very bad memory and forgets things easily.
“Oh, I forgot to buy the bread – I’ve got a brain like a sieve these days!”

have (something) down pat

If you memorise or practise something until you know it perfectly or have it exactly right, you have it down pat.)
“I rehearsed my presentation until I had it down pat.”

have (something) on the brain

If you have something on the brain, you think or talk abut it all constantly.A
“Stop talking about golf. You’ve got golf on the brain!”

go in one ear and come out the other

To say that information goes in one ear and comes out the other means that it is immediately forgotten or ignored.
“I keep telling him about the risks but it goes in one ear and out the other. He never listens!”

jog someone’s memory

When you help someone to remember something they have forgotten, you jog their memory.
“You don’t remember who was with us that day? Here’s a photograph to jog your memory.”

lose your train of thought

If you forget what you were saying, for example after a disturbance or interruption, you lose your train of thought.
“Now where was I? I’m afraid I’ve lost my train of thought.

if my memory serves me well

If your memory serves you well, you remember correctly or you have not forgotten any details.
“You’re Stella’s daughter, if my memory serves me well.

(take a) trip down memory lane

If you take a trip (stroll or walk) down memory lane, you remember pleasant things that happened in the past.
“Every Christmas is a trip down memory lane for the family when our parents take out the photograph albums.”

in your mind’s eye

If you can visualise something, or see an image of it in your mind, you see it in your mind’s eye.
“I can see the village in my mind’s eye but I can’t remember the name.”

refresh someone’s memory

If you refresh someone’s memory, you remind them of facts they seem to have forgotten.
“Let me refresh your memory – you’ve already missed three classes this term.”

ring a bell

If something rings a bell, it sounds familiar, but you don’t remember the exact details.
“John Bentley? The name rings a bell but I don’t remember him.”

(have a) senior moment

A momentary lapse of memory, especially in older people, or an absent-minded action such as putting the cereals in the refrigerator, is humorously referred to as having a senior moment.
“I found the phone in the cupboard. I must have had a senior moment!”

it slipped my mind

If something has slipped your mind, you have forgotten about it.
“Oh dear! It slipped my mind that the shops were closed today!”