They have so far not pin pointed exactly the point where that happens.Knowing that the nerves and spinal column are one of the first things that does develop and that a baby has about 3X the nerve endings that it will end of being born with before 7 months gestation IMHO it is much sooner than anyone would like to admit.My uneducated non medical school opinion would be at about 5 weeks gestation.
“The fifth week of pregnancy, or the third week after conception, marks the beginning of the embryonic period. This is when the baby’s brain, spinal cord, heart and other organs begin to form”
http://www.mayoclinic.com/health/prenatal-care/PR00112
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