Interesting reading.....
In addition, I've read that higher levels of TgAB and FT3 can be detrimental:
Significant positive correlations were found between free T3 levels and processing speed as well as between TgAB levels and error rates on the executive function tests. More specifically, higher levels of free T3 were positively associated with longer completion times (or slower performance) on Trail Making Test. Higher levels of free T3 were also associated with slower completion times on the Tower of London test. Furthermore, higher levels of TgAB were positively correlated with more errors on the Trail Making Test, on the Word Fluency test, and on the Design Fluency test.