▁ ▁The ▁varying ▁techniques ▁of ▁imag ing - based ▁testing ▁search ▁for ▁different ▁signs ▁of ▁intelligence . ▁The ▁types ▁of ▁intelligence ▁analyz ed ▁in ▁this ▁review ▁were ▁fluid ▁intelligence ▁( G f ), ▁general ▁intelligence ▁( g ), ▁and ▁cry st all ized ▁intelligence ▁( G c ). ▁Early ▁studies ▁util ized ▁information ▁from ▁patients ▁with ▁brain ▁damage , ▁not icing ▁changes ▁in ▁intelligence ▁scores ▁that ▁correl ated ▁to ▁certain ▁regions ▁of ▁the ▁brain . ▁As ▁imag ing ▁technology ▁has ▁improved , ▁so ▁has ▁the ▁ability ▁for ▁deeper ▁ne uro - analysis . ▁M RI ▁studies ▁have ▁found ▁that ▁the ▁volume ▁of ▁gray ▁matter ▁correl ates ▁to ▁intelligence , ▁providing ▁evidence ▁for ▁general izations ▁made ▁regarding ▁brain / head - size ▁and ▁intelligence . ▁Additionally , ▁P ET ▁and ▁f M RI ▁studies ▁have ▁revealed ▁more ▁information ▁regarding ▁the ▁functionality ▁of ▁certain ▁regions ▁of ▁the ▁brain . ▁By ▁recording ▁and ▁interpre ting ▁the ▁brain ▁activity ▁of ▁subjects ▁as ▁they ▁complete ▁a ▁variety ▁of ▁tasks , ▁research ers ▁are ▁able ▁to ▁draw ▁connections ▁between ▁the ▁types ▁of ▁task ▁( and ▁thus , ▁the ▁type ▁of ▁intelligence ) ▁that ▁calls ▁on ▁particular ▁areas ▁of ▁the ▁brain . ▁ ▁This ▁is ▁interesting ▁as ▁knowing ▁how ▁parts ▁of ▁the ▁brain ▁are ▁util ized ▁may ▁reve al ▁more ▁information ▁about ▁the ▁structure ▁and ▁hierarchy ▁used ▁in ▁neural ▁development . ▁It ▁also ▁may ▁provide ▁interesting ▁information ▁regarding ▁the ▁path ways ▁of ▁neural ▁signals ▁as ▁they ▁navigate ▁the ▁nerv ous ▁system . ▁Image - based ▁testing ▁may ▁allow ▁research ers