Well okay.
Let’s say you’re a helpful person and you help people out. Each time you help someone out, your brain goes “HEY COOL, HAVE A COOKIE!” and you’re happy.
Then a scientist comes and does some brain scans while stimulating the subject with fun things. The subject’s brain goes “HEY COOL, HAVE A COOKIE!”. Scientist notes that “HEY COOL, HAVE A COOKIE!” = happy person.
Then that scientist scans the brain of a bunch of charitable people. Their brains go “HEY COOL, HAVE A COOKIE!”. Science concludes that Charity = happy people
But, let’s say that you’re a pissed off person and you like to beat people up. Each time you beat people up, you’re happy and your brain goes “HEY COOL, HAVE A COOKIE!”. The same kind of “HEY COOL, HAVE A COOKIE!” as the previous ones, because this person is equally happy as the helpful person.
So my point is: people have different hotspots to trigger the “HEY COOL, HAVE A COOKIE!”-effect. You might be happy when you just gave money to charity and your brain might go “HEY COOL, HAVE A COOKIE!”. But I’m happy when I can keep my money to myself while my brain goes “HEY COOL, HAVE A COOKIE!”. I’ll also be happy when I was able to help someone I care for, my brain will also go “HEY COOL, HAVE A COOKIE!” for that. But it sure as hell doesn’t go “HEY COOL, HAVE A COOKIE!” when I just got ripped off for charity.
PS: some lie detectors use transpiration, others use heartbeats, others use brainsignals. All of them are pretty wonky.