Walking into a room and completely forgetting why you went in there is completely normal, says a top scientist. Cognitive neuroscientist Christian Jarrett explains the reason behind the “doorway effect”, which varies in significance based upon where you enter.

"Fear not, you’re far from the only one to have had this rather unsettling experience," Jarrett said in his column for BBC’s Science Focus. The doorway effect, a term used to describe when people forget their initial purpose for entering a new room, takes place when our brains compartmentalise activities and information based on our surroundings.

When moving from room to room, the door connecting the two acts like a metaphorical boundary, the scientist explains. The brain will update based upon its current understanding of the new location, which often has a different purpose to the room prior - for example, a bathroom and a bedroom.

Mr Jarrett referenced a team at the University of Queensland who explored the strange effect further. "They found that passing through doorways that joined identical rooms mostly didn’t impact memory – perhaps because there wasn’t enough of a changed context to create a significant event boundary," he said.

However, when the researchers distracted their volunteers with a simultaneous secondary task when moving between rooms, they realised it affected memory.

"The Queensland team said this chimes with everyday experience in that it’s mostly when we’re distracted, with our mind on other things, that we’re inclined to arrive in a room and forget what we came for,” he added.

Mr Jarrett said that the study also suggested that “the doorway effect is more likely to occur when there is a significant change in context – for instance, if you leave your living room for the garden”.

The scientist advised to try and “stay focused on your purpose when you pass through a doorway on an errand”. He added that taking down notes on the back of your hand or on your phone can help to keep track of errands too.