If you think your darling 11 year old has suddenly become someone your unfamiliar with, there is new research to support your suspicion........

Here are some ideas of note...

Teenage angst and clashes with authority may be caused by changes in youngsters' brains during puberty, but luckily for harassed parents the problems pass.

The ability of boys and girls to decode social cues and recognize emotions, particularly anger and sadness, dips between the ages of 12 and 14, researchers at University College London and the Institute of Child Health have discovered. "It would appear that this is a function of the development of their brain at that time," Professor David Skuse, of the group's behavioral science unit, told a conference on Thursday.

"It is a real biologically based phenomenon from which, fortunately, they recover," he added.

So rather than rebellious teenagers being deliberately obstinate or difficult, their brains may be unable to detect subtle signs from parents, teachers and other adults or to decode them correctly.

The same brain circuits involved in recognizing facial expression are also associated with processing tone of voice, according to Skuse.

"The ability to interpret your irritated tone of voice, the ability to interpret your angry facial expression may well deteriorate during that period of early adolescence," he added. But the problem seems to disappear by the age of 16 or 17.