[R] Question on: Random Forest Variable Importance for Regression Problems

[Mareike Ließ]

I am trying to use the package RandomForest performing regression.
The variable importance estimates are given as:  "%IncMSE"     and      
"IncNodePurity"
Can anyone explain me what these refer to and how they are calculated?
I found a lot of information on variable importance measures for 
classification problems, but nothing on regression.

Thanks a lot.
Mareike