Yoga and Stress

I have often been told by yoga teachers that yoga lifts stress and depression due to unexpressed emotions being given a safe space to be felt in the body and that this is one way trauma can be healed effectively. I have been told that yoga creates a safe environment in our bodies to feel what has been suppressed, allowing the circuit to be completed, as it were.

What if anger is an emotion which has gone unexpressed? 
Anger is a messy emotion. It feels tight in the body and doesn't want to be controlled by a yoga practice.
If you have been traumatized - and who hasn't to some degree - the tendency is to shut down and not complete the cycle. 

If someone has been abused to any degree and not expressed what they felt in that moment, i.e. rage, then that trauma creates problems down the line. If you know anyone who feels things fully when they come up you will probably notice they do not usually suffer from chronic bad moods. They feel things intensely and move on.

There are two sides to this story. Another, more 'scientific' view of what actually happens when we practice yoga is that our 'logical brain' is 'given a workout' and quietens down the negative 'emotional brain'. 

When the emotional brain is triggered by stress it goes into negative overload and the logical brain is unable to switch it off. The stress system impairs the serotonin, noradrenalin and dopamine signals and they become under-active. 

When we practice yoga we give the logical brain a 'workout' and can then quieten down the emotional brain.