Hello @scienceblocks 😃

<blockquote>what happens to psysiological changes in brain that were caused by that memory</blockquote>

<blockquote>Do they reverse?</blockquote>

It is important to understand that here we are not talking about memories being deleted or forgotten (also, this post does not cover trauma, dissociation etc..). We are talking about adopting strategies (e.g. having a plan) that might help people change their negative feelings/low mood towards their troubling memories. It is the change in their mood that, in turn, changes their brain activity (related to the limbic system, neurotransmitters etc..). 

For example, is not this one of the reasons why it is recommended that people living with depression engage in some form of exercise (endorphin, dopamine = mood boost). It is because of this very 'mood boost' that people begin to present improvement in both mental and physical health :)

It is a beautiful process.