What happens in the brain to make us 'catch' yawns

You may well be yawning just reading this - it's contagious. Now researchers have looked at what happens in our brains to trigger that response.
A University of Nottingham team found it occurs in a part of the brain responsible for motor function.
The primary motor cortex also plays a part in conditions such as Tourette's syndrome.
So the scientists say understanding contagious yawning could also help understand those disorders too.
Contagious yawning is a common form of echophenomena - the automatic imitation of someone else's words or actions.
Echophenomena is also seen in Tourette's, as well as in other conditions, including epilepsy and autism.
To test what's happening in the brain during the phenomenon, scientists monitored 36 volunteers while they watched others yawning.
'Excitability'
In the study, published in the journal Current Biology, some were told it was fine to yawn while others were told to stifle the urge.
The urge to yawn was down to how each person's primary motor cortex worked - its "excitability".
And, using external transcranial magnetic stimulation (TMS), it was also possible to increase "excitability" in the motor cortex and therefore people's propensity for contagious yawns.