Beyond that, they don't say why they only looked at the PCC. I wonder if they looked at other parts of the brain.
The methods section says they looked at all of these molecules:
Alanine, Aspartate, Cr, PCr, γ-Aminobutyric acid (GABA), Glucose, Gln, Glu, GPC, PCh, Glutathione, Ins, Lactate...