First of all, i’d like to welcome you to the forum Virg80!
The Plasma Brain of Youth is a bonus field that you get if you buy the field “How Smart are Stem Cells?”
Here is the gumroad link: https://sapienmedicine.gumroad.com/l/RUzeC?layout=profile
Next time you have another question, you can use the search bar using the magnifying glass at the top right corner of the the webpage to find what you’re looking for.
Here is the thread for the field “How Smart are Stem Cells?”: https://forum.enlightenedstates.com/t/how-smart-are-stem-cells/11843