Trying to do more than two things at once causes us to perform all the tasks poorly, according to new research into how the human brain operates.

French scientists have discovered that the brain effectively splits itself into two parts when dealing with two tasks at once.

Brain scans on study volunteers revealed that one side of a part of the frontal lobes lit up when they were doing one task.

When volunteers did two tasks at once the lobes split the tasks between them, with the left frontal lobe focusing on the main task and the right frontal lobe focusing on the secondary task.

This allowed them to carry out both tasks at normal efficiency.

However, when a third task was added, the performance of all tasks suffered.

“What really the results show is that we can readily divide tasking. We can cook, and at the same time talk on the phone, and switch back and forth between these two activities,” said study researcher Etienne Koechlin of the Université Pierre et Marie Curie in Paris.

“However, we cannot multitask with more than two tasks.”

The results are in the latest edition of the journal Science.