The science of electronic brain implants is only in its infancy, and so the receptiveness of the host to such an invasive procedure is varied. Depending on the individual and how the surgery went, the implant may be more or less usable to the Aquanaut. This is the soldier's M.C. Strength, a constant value which cannot ever be changed.
New recruits will always begin with a value between 0 and 100 (inclusive). Your soldier's M.C. Strength will not be revealed until his or her first month of M.C.-Lab training is complete.
Prior to gaining M.C. technology, if you have soldiers who are consistently panicked or mind controlled by aliens, it's a very good bet that they will have low M.C. Strength (below 60). (Aliens 'peek' and know who's low.) Don't strip such soldiers of their weapons, and use them as scouts or cannon fodder, just fire them and get new soldiers. After one month of M.C. training you know who is going to stay and who is going to be sacked.
As a consolation prize, soldiers who have panicked many times are liable to see their Bravery increase.