When you enter a room for a reason but then can’t for the life of you remember why, you’re experiencing an eerie feature of the mind’s energy-saving economy.
The “doorway effect” is the term used for when parts of your short-term memory get wiped clean whenever you enter a new location—even if it’s a virtual one.
Your “working memory” is the part of your short-term memory circuitry that holds information for the here and now. It can hold between only three and seven different things at a time. Entering a new location tells the brain the situation has changed and that those chunks of information are no longer relevant, so it’s safe to discard them to make room for new things. It’s a healthy way for the brain to make the most efficient use of your limited temporary memory.
The doorway effect happens just as often in the young and old so needn’t cause you to fret that your memory is failing. Return to the original room or retrace your steps mentally, and you will often recall or figure out the thought process that led you here.
Entering a new room often tells the brain to start afresh to free up space for new information. The more tasks you are trying to remember, the more likely it is that you will be at the mercy of the doorway effect.