It's a phenomenon known as performance monitoring; an internal signal produced by the brain that lets you know when you've made a mistake.

Performance monitoring is a kind of self-generated feedback that's essential to managing our daily lives. Now, neuroscientists have discovered that signals from neurons in the brain's medial frontal cortex are responsible for it.

A new study published in Science reports that these signals are used to give humans the flexibility to learn new tasks and the focus to develop highly specific skills.

"Part of the magic of the human brain is that it is so flexible," says senior author Ueli Rutishauser, professor of Neurosurgery, Neurology, and Biomedical Sciences at Cedars-Sinai Medical Center, US.

"We designed our study to decipher how the brain can generalise and specialise at the same time, both of which are critical for helping us pursue a goal."

They found that the performance monitoring signals help improve future attempts of a particular task by passing information to other areas of the brain.

They also help the brain adjust its focus by signalling how much conflict or difficulty was encountered during the task.

"An 'Oops!' moment might prompt someone to pay closer attention the next time they chat with a friend, or plan to stop at the store on the way home from work," explains first author Zhongzheng Fu, researcher in the Rutishauser Laboratory at Cedars-Sinai.

The team recorded the activity of more than 1000 neurons in the medial frontal cortexes of human epilepsy patients (who had existing electrode brain implants to help locate the focus of their seizures) while they performed complex cognitive tasks.

In the first task, called the Stroop task, participants' reading- and colour naming skills were tested. Viewing the written name of the colour, such as "red", printed in the ink of a different colour, such as blue, they were asked to name the ink colour rather than the written word.

In the second task - the Multi-Source Interference Task (MSIT) - participants were shown three digits on a screen (two the same number and the other unique) and had to press a button associated with the unique number while resisting the tendency to press the other (because it appears twice).

The researchers noted that two types of neurons seemed to be at work: "error" neurons fired strongly after a mistake was made, while "conflict" neurons fired in response to the difficulty of the task.

"When we observed the activity of neurons in this brain area, it surprised us that most of them only become active after a decision or an action was completed," says Fu.

"This indicates that this brain area plays a role in evaluating decisions after the fact, rather than making them."

Scientists have known for some time that there are two types of performance monitoring: domain general and domain specific.

Domain general performance monitoring tells us when something goes wrong, which allows people to perform new tasks with little instruction.

Domain specific monitoring tells them what went wrong, and is one way that people perfect individual skills.

Previously it was thought that the different neurons responsible for these two forms were located in distinct parts of the brain, but this research has found that they're actually intermingled in the medial frontal cortex.

According to Rutishauser, understanding the mechanisms behind performance monitoring is critical to perfecting the treatment of certain psychiatric disorders in which it is extreme, for example obsessive compulsive disorder (overactive monitoring) and schizophrenia (underactive).