London, Sep 19 (IANS) Have you ever wondered why we sometimes 'freeze' when we are frightened or under strong emotional stress? This may be because the response to anxiety may include not only the parts of the brain which deal with emotions, as has been long understood, but also movement control centres in the brain.

"This (study) is the first hard proof that strong emotions produce a response in brain areas concerned with movement," said lead researcher Laura Muzzarelli from Vita-Salute San Raffaele University in Milan, Italy.

The findings give us "a possible explanation for some motor inhibition associated with emotional stress", she added.

For the study, a group of Italian and Canadian researchers followed a selection of socially anxious and control group children from childhood to adolescence. 

The researchers tested 150 children who were between ages of eight to nine, for signs of social inhibition.

Some of these were shown to have early signs of social anxiety, and showed an increased tendency to withdraw from social situations. 

They also had more difficulty in recognising emotions, and particularly angry faces.

The anxious children, plus controls, were then followed into adolescence. At the ages of 14-15 they were tested again to see if signs of social anxiety had developed. 

The researchers also used functional MRI brain scans to test how the teenage brains responded to angry facial expressions.

"We found that when presented with an angry face the brain of socially anxious adolescents showed increased activity in the amygdala, which is the brain area concerned with emotions, memory and how we respond to threats," Muzzarelli said.

"Surprisingly, we also found this produced inhibition of some motor areas of the brain, the premotor cortex. This is an area which 'prepares the body for action', and for specific movements," she noted. 

The findings were presented at the ongoing European College of Neuropsychopharmacology (ECNP) conference in Vienna, Austria.